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runtime: reorganize memory code

Browse source 
Move code from malloc1.go, malloc2.go, mem.go, mgc0.go into
appropriate locations.

Factor mgc.go into mgc.go, mgcmark.go, mgcsweep.go, mstats.go.

A lot of this code was in certain files because the right place was in
a C file but it was written in Go, or vice versa. This is one step toward
making things actually well-organized again.

Change-Id: I6741deb88a7cfb1c17ffe0bcca3989e10207968f
Reviewed-on: https://go-review.googlesource.com/5300
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Russ Cox 2015-02-19 13:38:46 -05:00
parent d384545a45
commit 484f801ff4
20 changed files with 2567 additions and 2593 deletions
Download patch file Download diff file Expand all files Collapse all files

18
src/runtime/heapdump.go
View file

@ -13,6 +13,24 @@ package runtime
import "unsafe"
//go:linkname runtime_debug_WriteHeapDump runtime/debug.WriteHeapDump
func runtime_debug_WriteHeapDump(fd uintptr) {
semacquire(&worldsema, false)
gp := getg()
gp.m.preemptoff = "write heap dump"
systemstack(stoptheworld)
systemstack(func() {
writeheapdump_m(fd)
})
gp.m.preemptoff = ""
gp.m.locks++
semrelease(&worldsema)
systemstack(starttheworld)
gp.m.locks--
}
const (
fieldKindEol = 0
fieldKindPtr = 1

754
src/runtime/malloc.go
View file

@ -2,6 +2,84 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Memory allocator, based on tcmalloc.
// http://goog-perftools.sourceforge.net/doc/tcmalloc.html
// The main allocator works in runs of pages.
// Small allocation sizes (up to and including 32 kB) are
// rounded to one of about 100 size classes, each of which
// has its own free list of objects of exactly that size.
// Any free page of memory can be split into a set of objects
// of one size class, which are then managed using free list
// allocators.
//
// The allocator's data structures are:
//
// FixAlloc: a free-list allocator for fixed-size objects,
// used to manage storage used by the allocator.
// MHeap: the malloc heap, managed at page (4096-byte) granularity.
// MSpan: a run of pages managed by the MHeap.
// MCentral: a shared free list for a given size class.
// MCache: a per-thread (in Go, per-P) cache for small objects.
// MStats: allocation statistics.
//
// Allocating a small object proceeds up a hierarchy of caches:
//
// 1. Round the size up to one of the small size classes
// and look in the corresponding MCache free list.
// If the list is not empty, allocate an object from it.
// This can all be done without acquiring a lock.
//
// 2. If the MCache free list is empty, replenish it by
// taking a bunch of objects from the MCentral free list.
// Moving a bunch amortizes the cost of acquiring the MCentral lock.
//
// 3. If the MCentral free list is empty, replenish it by
// allocating a run of pages from the MHeap and then
// chopping that memory into objects of the given size.
// Allocating many objects amortizes the cost of locking
// the heap.
//
// 4. If the MHeap is empty or has no page runs large enough,
// allocate a new group of pages (at least 1MB) from the
// operating system. Allocating a large run of pages
// amortizes the cost of talking to the operating system.
//
// Freeing a small object proceeds up the same hierarchy:
//
// 1. Look up the size class for the object and add it to
// the MCache free list.
//
// 2. If the MCache free list is too long or the MCache has
// too much memory, return some to the MCentral free lists.
//
// 3. If all the objects in a given span have returned to
// the MCentral list, return that span to the page heap.
//
// 4. If the heap has too much memory, return some to the
// operating system.
//
// TODO(rsc): Step 4 is not implemented.
//
// Allocating and freeing a large object uses the page heap
// directly, bypassing the MCache and MCentral free lists.
//
// The small objects on the MCache and MCentral free lists
// may or may not be zeroed. They are zeroed if and only if
// the second word of the object is zero. A span in the
// page heap is zeroed unless s->needzero is set. When a span
// is allocated to break into small objects, it is zeroed if needed
// and s->needzero is set. There are two main benefits to delaying the
// zeroing this way:
//
// 1. stack frames allocated from the small object lists
// or the page heap can avoid zeroing altogether.
// 2. the cost of zeroing when reusing a small object is
// charged to the mutator, not the garbage collector.
//
// This code was written with an eye toward translating to Go
// in the future. Methods have the form Type_Method(Type *t, ...).
package runtime
import "unsafe"
@ -25,29 +103,369 @@ const (
concurrentSweep = _ConcurrentSweep
)
const (
_PageShift = 13
_PageSize = 1 << _PageShift
_PageMask = _PageSize - 1
)
const (
// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
_64bit = 1 << (^uintptr(0) >> 63) / 2
// Computed constant. The definition of MaxSmallSize and the
// algorithm in msize.c produce some number of different allocation
// size classes. NumSizeClasses is that number. It's needed here
// because there are static arrays of this length; when msize runs its
// size choosing algorithm it double-checks that NumSizeClasses agrees.
_NumSizeClasses = 67
// Tunable constants.
_MaxSmallSize = 32 << 10
// Tiny allocator parameters, see "Tiny allocator" comment in malloc.go.
_TinySize = 16
_TinySizeClass = 2
_FixAllocChunk = 16 << 10 // Chunk size for FixAlloc
_MaxMHeapList = 1 << (20 - _PageShift) // Maximum page length for fixed-size list in MHeap.
_HeapAllocChunk = 1 << 20 // Chunk size for heap growth
// Per-P, per order stack segment cache size.
_StackCacheSize = 32 * 1024
// Number of orders that get caching. Order 0 is FixedStack
// and each successive order is twice as large.
// We want to cache 2KB, 4KB, 8KB, and 16KB stacks. Larger stacks
// will be allocated directly.
// Since FixedStack is different on different systems, we
// must vary NumStackOrders to keep the same maximum cached size.
// OS | FixedStack | NumStackOrders
// -----------------+------------+---------------
// linux/darwin/bsd | 2KB | 4
// windows/32 | 4KB | 3
// windows/64 | 8KB | 2
// plan9 | 4KB | 3
_NumStackOrders = 4 - ptrSize/4*goos_windows - 1*goos_plan9
// Number of bits in page to span calculations (4k pages).
// On Windows 64-bit we limit the arena to 32GB or 35 bits.
// Windows counts memory used by page table into committed memory
// of the process, so we can't reserve too much memory.
// See http://golang.org/issue/5402 and http://golang.org/issue/5236.
// On other 64-bit platforms, we limit the arena to 128GB, or 37 bits.
// On 32-bit, we don't bother limiting anything, so we use the full 32-bit address.
_MHeapMap_TotalBits = (_64bit*goos_windows)*35 + (_64bit*(1-goos_windows))*37 + (1-_64bit)*32
_MHeapMap_Bits = _MHeapMap_TotalBits - _PageShift
_MaxMem = uintptr(1<<_MHeapMap_TotalBits - 1)
// Max number of threads to run garbage collection.
// 2, 3, and 4 are all plausible maximums depending
// on the hardware details of the machine. The garbage
// collector scales well to 32 cpus.
_MaxGcproc = 32
)
// Page number (address>>pageShift)
type pageID uintptr
const _MaxArena32 = 2 << 30
// OS-defined helpers:
//
// sysAlloc obtains a large chunk of zeroed memory from the
// operating system, typically on the order of a hundred kilobytes
// or a megabyte.
// NOTE: sysAlloc returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysUnused notifies the operating system that the contents
// of the memory region are no longer needed and can be reused
// for other purposes.
// SysUsed notifies the operating system that the contents
// of the memory region are needed again.
//
// SysFree returns it unconditionally; this is only used if
// an out-of-memory error has been detected midway through
// an allocation. It is okay if SysFree is a no-op.
//
// SysReserve reserves address space without allocating memory.
// If the pointer passed to it is non-nil, the caller wants the
// reservation there, but SysReserve can still choose another
// location if that one is unavailable. On some systems and in some
// cases SysReserve will simply check that the address space is
// available and not actually reserve it. If SysReserve returns
// non-nil, it sets *reserved to true if the address space is
// reserved, false if it has merely been checked.
// NOTE: SysReserve returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysMap maps previously reserved address space for use.
// The reserved argument is true if the address space was really
// reserved, not merely checked.
//
// SysFault marks a (already sysAlloc'd) region to fault
// if accessed. Used only for debugging the runtime.
func mallocinit() {
initSizes()
if class_to_size[_TinySizeClass] != _TinySize {
throw("bad TinySizeClass")
}
var p, bitmapSize, spansSize, pSize, limit uintptr
var reserved bool
// limit = runtime.memlimit();
// See https://golang.org/issue/5049
// TODO(rsc): Fix after 1.1.
limit = 0
// Set up the allocation arena, a contiguous area of memory where
// allocated data will be found. The arena begins with a bitmap large
// enough to hold 4 bits per allocated word.
if ptrSize == 8 && (limit == 0 || limit > 1<<30) {
// On a 64-bit machine, allocate from a single contiguous reservation.
// 128 GB (MaxMem) should be big enough for now.
//
// The code will work with the reservation at any address, but ask
// SysReserve to use 0x0000XXc000000000 if possible (XX=00...7f).
// Allocating a 128 GB region takes away 37 bits, and the amd64
// doesn't let us choose the top 17 bits, so that leaves the 11 bits
// in the middle of 0x00c0 for us to choose. Choosing 0x00c0 means
// that the valid memory addresses will begin 0x00c0, 0x00c1, ..., 0x00df.
// In little-endian, that's c0 00, c1 00, ..., df 00. None of those are valid
// UTF-8 sequences, and they are otherwise as far away from
// ff (likely a common byte) as possible. If that fails, we try other 0xXXc0
// addresses. An earlier attempt to use 0x11f8 caused out of memory errors
// on OS X during thread allocations. 0x00c0 causes conflicts with
// AddressSanitizer which reserves all memory up to 0x0100.
// These choices are both for debuggability and to reduce the
// odds of the conservative garbage collector not collecting memory
// because some non-pointer block of memory had a bit pattern
// that matched a memory address.
//
// Actually we reserve 136 GB (because the bitmap ends up being 8 GB)
// but it hardly matters: e0 00 is not valid UTF-8 either.
//
// If this fails we fall back to the 32 bit memory mechanism
arenaSize := round(_MaxMem, _PageSize)
bitmapSize = arenaSize / (ptrSize * 8 / 4)
spansSize = arenaSize / _PageSize * ptrSize
spansSize = round(spansSize, _PageSize)
for i := 0; i <= 0x7f; i++ {
p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
}
if p == 0 {
// On a 32-bit machine, we can't typically get away
// with a giant virtual address space reservation.
// Instead we map the memory information bitmap
// immediately after the data segment, large enough
// to handle another 2GB of mappings (256 MB),
// along with a reservation for an initial arena.
// When that gets used up, we'll start asking the kernel
// for any memory anywhere and hope it's in the 2GB
// following the bitmap (presumably the executable begins
// near the bottom of memory, so we'll have to use up
// most of memory before the kernel resorts to giving out
// memory before the beginning of the text segment).
//
// Alternatively we could reserve 512 MB bitmap, enough
// for 4GB of mappings, and then accept any memory the
// kernel threw at us, but normally that's a waste of 512 MB
// of address space, which is probably too much in a 32-bit world.
// If we fail to allocate, try again with a smaller arena.
// This is necessary on Android L where we share a process
// with ART, which reserves virtual memory aggressively.
arenaSizes := []uintptr{
512 << 20,
256 << 20,
}
for _, arenaSize := range arenaSizes {
bitmapSize = _MaxArena32 / (ptrSize * 8 / 4)
spansSize = _MaxArena32 / _PageSize * ptrSize
if limit > 0 && arenaSize+bitmapSize+spansSize > limit {
bitmapSize = (limit / 9) &^ ((1 << _PageShift) - 1)
arenaSize = bitmapSize * 8
spansSize = arenaSize / _PageSize * ptrSize
}
spansSize = round(spansSize, _PageSize)
// SysReserve treats the address we ask for, end, as a hint,
// not as an absolute requirement. If we ask for the end
// of the data segment but the operating system requires
// a little more space before we can start allocating, it will
// give out a slightly higher pointer. Except QEMU, which
// is buggy, as usual: it won't adjust the pointer upward.
// So adjust it upward a little bit ourselves: 1/4 MB to get
// away from the running binary image and then round up
// to a MB boundary.
p = round(uintptr(unsafe.Pointer(&end))+(1<<18), 1<<20)
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
if p == 0 {
throw("runtime: cannot reserve arena virtual address space")
}
}
// PageSize can be larger than OS definition of page size,
// so SysReserve can give us a PageSize-unaligned pointer.
// To overcome this we ask for PageSize more and round up the pointer.
p1 := round(p, _PageSize)
mheap_.spans = (**mspan)(unsafe.Pointer(p1))
mheap_.bitmap = p1 + spansSize
mheap_.arena_start = p1 + (spansSize + bitmapSize)
mheap_.arena_used = mheap_.arena_start
mheap_.arena_end = p + pSize
mheap_.arena_reserved = reserved
if mheap_.arena_start&(_PageSize-1) != 0 {
println("bad pagesize", hex(p), hex(p1), hex(spansSize), hex(bitmapSize), hex(_PageSize), "start", hex(mheap_.arena_start))
throw("misrounded allocation in mallocinit")
}
// Initialize the rest of the allocator.
mHeap_Init(&mheap_, spansSize)
_g_ := getg()
_g_.m.mcache = allocmcache()
}
// sysReserveHigh reserves space somewhere high in the address space.
// sysReserve doesn't actually reserve the full amount requested on
// 64-bit systems, because of problems with ulimit. Instead it checks
// that it can get the first 64 kB and assumes it can grab the rest as
// needed. This doesn't work well with the "let the kernel pick an address"
// mode, so don't do that. Pick a high address instead.
func sysReserveHigh(n uintptr, reserved *bool) unsafe.Pointer {
if ptrSize == 4 {
return sysReserve(nil, n, reserved)
}
for i := 0; i <= 0x7f; i++ {
p := uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
*reserved = false
p = uintptr(sysReserve(unsafe.Pointer(p), n, reserved))
if p != 0 {
return unsafe.Pointer(p)
}
}
return sysReserve(nil, n, reserved)
}
func mHeap_SysAlloc(h *mheap, n uintptr) unsafe.Pointer {
if n > uintptr(h.arena_end)-uintptr(h.arena_used) {
// We are in 32-bit mode, maybe we didn't use all possible address space yet.
// Reserve some more space.
p_size := round(n+_PageSize, 256<<20)
new_end := h.arena_end + p_size
if new_end <= h.arena_start+_MaxArena32 {
// TODO: It would be bad if part of the arena
// is reserved and part is not.
var reserved bool
p := uintptr(sysReserve((unsafe.Pointer)(h.arena_end), p_size, &reserved))
if p == h.arena_end {
h.arena_end = new_end
h.arena_reserved = reserved
} else if p+p_size <= h.arena_start+_MaxArena32 {
// Keep everything page-aligned.
// Our pages are bigger than hardware pages.
h.arena_end = p + p_size
h.arena_used = p + (-uintptr(p) & (_PageSize - 1))
h.arena_reserved = reserved
} else {
var stat uint64
sysFree((unsafe.Pointer)(p), p_size, &stat)
}
}
}
if n <= uintptr(h.arena_end)-uintptr(h.arena_used) {
// Keep taking from our reservation.
p := h.arena_used
sysMap((unsafe.Pointer)(p), n, h.arena_reserved, &memstats.heap_sys)
h.arena_used += n
mHeap_MapBits(h)
mHeap_MapSpans(h)
if raceenabled {
racemapshadow((unsafe.Pointer)(p), n)
}
if mheap_.shadow_enabled {
sysMap(unsafe.Pointer(p+mheap_.shadow_heap), n, h.shadow_reserved, &memstats.other_sys)
}
if uintptr(p)&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return (unsafe.Pointer)(p)
}
// If using 64-bit, our reservation is all we have.
if uintptr(h.arena_end)-uintptr(h.arena_start) >= _MaxArena32 {
return nil
}
// On 32-bit, once the reservation is gone we can
// try to get memory at a location chosen by the OS
// and hope that it is in the range we allocated bitmap for.
p_size := round(n, _PageSize) + _PageSize
p := uintptr(sysAlloc(p_size, &memstats.heap_sys))
if p == 0 {
return nil
}
if p < h.arena_start || uintptr(p)+p_size-uintptr(h.arena_start) >= _MaxArena32 {
print("runtime: memory allocated by OS (", p, ") not in usable range [", hex(h.arena_start), ",", hex(h.arena_start+_MaxArena32), ")\n")
sysFree((unsafe.Pointer)(p), p_size, &memstats.heap_sys)
return nil
}
p_end := p + p_size
p += -p & (_PageSize - 1)
if uintptr(p)+n > uintptr(h.arena_used) {
h.arena_used = p + n
if p_end > h.arena_end {
h.arena_end = p_end
}
mHeap_MapBits(h)
mHeap_MapSpans(h)
if raceenabled {
racemapshadow((unsafe.Pointer)(p), n)
}
}
if uintptr(p)&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return (unsafe.Pointer)(p)
}
// base address for all 0-byte allocations
var zerobase uintptr
// Trigger the concurrent GC when 1/triggerratio memory is available to allocate.
// Adjust this ratio as part of a scheme to ensure that mutators have enough
// memory to allocate in durring a concurrent GC cycle.
var triggerratio = int64(8)
// Determine whether to initiate a GC.
// If the GC is already working no need to trigger another one.
// This should establish a feedback loop where if the GC does not
// have sufficient time to complete then more memory will be
// requested from the OS increasing heap size thus allow future
// GCs more time to complete.
// memstat.heap_alloc and memstat.next_gc reads have benign races
// A false negative simple does not start a GC, a false positive
// will start a GC needlessly. Neither have correctness issues.
func shouldtriggergc() bool {
return triggerratio*(int64(memstats.next_gc)-int64(memstats.heap_alloc)) <= int64(memstats.next_gc) && atomicloaduint(&bggc.working) == 0
}
const (
// flags to malloc
_FlagNoScan = 1 << 0 // GC doesn't have to scan object
_FlagNoZero = 1 << 1 // don't zero memory
)
// Allocate an object of size bytes.
// Small objects are allocated from the per-P cache's free lists.
@ -250,6 +668,25 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
return x
}
func largeAlloc(size uintptr, flag uint32) *mspan {
// print("largeAlloc size=", size, "\n")
if size+_PageSize < size {
throw("out of memory")
}
npages := size >> _PageShift
if size&_PageMask != 0 {
npages++
}
s := mHeap_Alloc(&mheap_, npages, 0, true, flag&_FlagNoZero == 0)
if s == nil {
throw("out of memory")
}
s.limit = uintptr(s.start)<<_PageShift + size
heapBitsForSpan(s.base()).initSpan(s.layout())
return s
}
// implementation of new builtin
func newobject(typ *_type) unsafe.Pointer {
flags := uint32(0)
@ -310,289 +747,6 @@ func profilealloc(mp *m, x unsafe.Pointer, size uintptr) {
mProf_Malloc(x, size)
}
// For now this must be bracketed with a stoptheworld and a starttheworld to ensure
// all go routines see the new barrier.
//go:nowritebarrier
func gcinstallmarkwb() {
gcphase = _GCmark
}
// force = 0 - start concurrent GC
// force = 1 - do STW GC regardless of current heap usage
// force = 2 - go STW GC and eager sweep
func gogc(force int32) {
// The gc is turned off (via enablegc) until the bootstrap has completed.
// Also, malloc gets called in the guts of a number of libraries that might be
// holding locks. To avoid deadlocks during stoptheworld, don't bother
// trying to run gc while holding a lock. The next mallocgc without a lock
// will do the gc instead.
mp := acquirem()
if gp := getg(); gp == mp.g0 || mp.locks > 1 || !memstats.enablegc || panicking != 0 || gcpercent < 0 {
releasem(mp)
return
}
releasem(mp)
mp = nil
if force == 0 {
lock(&bggc.lock)
if !bggc.started {
bggc.working = 1
bggc.started = true
go backgroundgc()
} else if bggc.working == 0 {
bggc.working = 1
ready(bggc.g)
}
unlock(&bggc.lock)
} else {
gcwork(force)
}
}
func gcwork(force int32) {
semacquire(&worldsema, false)
// Pick up the remaining unswept/not being swept spans concurrently
for gosweepone() != ^uintptr(0) {
sweep.nbgsweep++
}
// Ok, we're doing it! Stop everybody else
mp := acquirem()
mp.preemptoff = "gcing"
releasem(mp)
gctimer.count++
if force == 0 {
gctimer.cycle.sweepterm = nanotime()
}
if trace.enabled {
traceGoSched()
traceGCStart()
}
// Pick up the remaining unswept/not being swept spans before we STW
for gosweepone() != ^uintptr(0) {
sweep.nbgsweep++
}
systemstack(stoptheworld)
systemstack(finishsweep_m) // finish sweep before we start concurrent scan.
if force == 0 { // Do as much work concurrently as possible
gcphase = _GCscan
systemstack(starttheworld)
gctimer.cycle.scan = nanotime()
// Do a concurrent heap scan before we stop the world.
systemstack(gcscan_m)
gctimer.cycle.installmarkwb = nanotime()
systemstack(stoptheworld)
systemstack(gcinstallmarkwb)
systemstack(harvestwbufs)
systemstack(starttheworld)
gctimer.cycle.mark = nanotime()
systemstack(gcmark_m)
gctimer.cycle.markterm = nanotime()
systemstack(stoptheworld)
systemstack(gcinstalloffwb_m)
} else {
// For non-concurrent GC (force != 0) g stack have not been scanned so
// set gcscanvalid such that mark termination scans all stacks.
// No races here since we are in a STW phase.
for _, gp := range allgs {
gp.gcworkdone = false // set to true in gcphasework
gp.gcscanvalid = false // stack has not been scanned
}
}
startTime := nanotime()
if mp != acquirem() {
throw("gogc: rescheduled")
}
clearpools()
// Run gc on the g0 stack. We do this so that the g stack
// we're currently running on will no longer change. Cuts
// the root set down a bit (g0 stacks are not scanned, and
// we don't need to scan gc's internal state). We also
// need to switch to g0 so we can shrink the stack.
n := 1
if debug.gctrace > 1 {
n = 2
}
eagersweep := force >= 2
for i := 0; i < n; i++ {
if i > 0 {
// refresh start time if doing a second GC
startTime = nanotime()
}
// switch to g0, call gc, then switch back
systemstack(func() {
gc_m(startTime, eagersweep)
})
}
systemstack(func() {
gccheckmark_m(startTime, eagersweep)
})
if trace.enabled {
traceGCDone()
traceGoStart()
}
// all done
mp.preemptoff = ""
if force == 0 {
gctimer.cycle.sweep = nanotime()
}
semrelease(&worldsema)
if force == 0 {
if gctimer.verbose > 1 {
GCprinttimes()
} else if gctimer.verbose > 0 {
calctimes() // ignore result
}
}
systemstack(starttheworld)
releasem(mp)
mp = nil
// now that gc is done, kick off finalizer thread if needed
if !concurrentSweep {
// give the queued finalizers, if any, a chance to run
Gosched()
}
}
// gctimes records the time in nanoseconds of each phase of the concurrent GC.
type gctimes struct {
sweepterm int64 // stw
scan int64
installmarkwb int64 // stw
mark int64
markterm int64 // stw
sweep int64
}
// gcchronograph holds timer information related to GC phases
// max records the maximum time spent in each GC phase since GCstarttimes.
// total records the total time spent in each GC phase since GCstarttimes.
// cycle records the absolute time (as returned by nanoseconds()) that each GC phase last started at.
type gcchronograph struct {
count int64
verbose int64
maxpause int64
max gctimes
total gctimes
cycle gctimes
}
var gctimer gcchronograph
// GCstarttimes initializes the gc times. All previous times are lost.
func GCstarttimes(verbose int64) {
gctimer = gcchronograph{verbose: verbose}
}
// GCendtimes stops the gc timers.
func GCendtimes() {
gctimer.verbose = 0
}
// calctimes converts gctimer.cycle into the elapsed times, updates gctimer.total
// and updates gctimer.max with the max pause time.
func calctimes() gctimes {
var times gctimes
var max = func(a, b int64) int64 {
if a > b {
return a
}
return b
}
times.sweepterm = gctimer.cycle.scan - gctimer.cycle.sweepterm
gctimer.total.sweepterm += times.sweepterm
gctimer.max.sweepterm = max(gctimer.max.sweepterm, times.sweepterm)
gctimer.maxpause = max(gctimer.maxpause, gctimer.max.sweepterm)
times.scan = gctimer.cycle.installmarkwb - gctimer.cycle.scan
gctimer.total.scan += times.scan
gctimer.max.scan = max(gctimer.max.scan, times.scan)
times.installmarkwb = gctimer.cycle.mark - gctimer.cycle.installmarkwb
gctimer.total.installmarkwb += times.installmarkwb
gctimer.max.installmarkwb = max(gctimer.max.installmarkwb, times.installmarkwb)
gctimer.maxpause = max(gctimer.maxpause, gctimer.max.installmarkwb)
times.mark = gctimer.cycle.markterm - gctimer.cycle.mark
gctimer.total.mark += times.mark
gctimer.max.mark = max(gctimer.max.mark, times.mark)
times.markterm = gctimer.cycle.sweep - gctimer.cycle.markterm
gctimer.total.markterm += times.markterm
gctimer.max.markterm = max(gctimer.max.markterm, times.markterm)
gctimer.maxpause = max(gctimer.maxpause, gctimer.max.markterm)
return times
}
// GCprinttimes prints latency information in nanoseconds about various
// phases in the GC. The information for each phase includes the maximum pause
// and total time since the most recent call to GCstarttimes as well as
// the information from the most recent Concurent GC cycle. Calls from the
// application to runtime.GC() are ignored.
func GCprinttimes() {
if gctimer.verbose == 0 {
println("GC timers not enabled")
return
}
// Explicitly put times on the heap so printPhase can use it.
times := new(gctimes)
*times = calctimes()
cycletime := gctimer.cycle.sweep - gctimer.cycle.sweepterm
pause := times.sweepterm + times.installmarkwb + times.markterm
gomaxprocs := GOMAXPROCS(-1)
printlock()
print("GC: #", gctimer.count, " ", cycletime, "ns @", gctimer.cycle.sweepterm, " pause=", pause, " maxpause=", gctimer.maxpause, " goroutines=", allglen, " gomaxprocs=", gomaxprocs, "\n")
printPhase := func(label string, get func(*gctimes) int64, procs int) {
print("GC: ", label, " ", get(times), "ns\tmax=", get(&gctimer.max), "\ttotal=", get(&gctimer.total), "\tprocs=", procs, "\n")
}
printPhase("sweep term:", func(t *gctimes) int64 { return t.sweepterm }, gomaxprocs)
printPhase("scan: ", func(t *gctimes) int64 { return t.scan }, 1)
printPhase("install wb:", func(t *gctimes) int64 { return t.installmarkwb }, gomaxprocs)
printPhase("mark: ", func(t *gctimes) int64 { return t.mark }, 1)
printPhase("mark term: ", func(t *gctimes) int64 { return t.markterm }, gomaxprocs)
printunlock()
}
// GC runs a garbage collection.
func GC() {
gogc(2)
}
// linker-provided
var noptrdata struct{}
var enoptrdata struct{}
var noptrbss struct{}
var enoptrbss struct{}
// round n up to a multiple of a. a must be a power of 2.
func round(n, a uintptr) uintptr {
return (n + a - 1) &^ (a - 1)
}
var persistent struct {
lock mutex
base unsafe.Pointer

358
src/runtime/malloc1.go
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@ -1,358 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// See malloc.h for overview.
//
// TODO(rsc): double-check stats.
package runtime
import "unsafe"
const _MaxArena32 = 2 << 30
// For use by Go. If it were a C enum it would be made available automatically,
// but the value of MaxMem is too large for enum.
// XXX - uintptr runtime·maxmem = MaxMem;
func mlookup(v uintptr, base *uintptr, size *uintptr, sp **mspan) int32 {
_g_ := getg()
_g_.m.mcache.local_nlookup++
if ptrSize == 4 && _g_.m.mcache.local_nlookup >= 1<<30 {
// purge cache stats to prevent overflow
lock(&mheap_.lock)
purgecachedstats(_g_.m.mcache)
unlock(&mheap_.lock)
}
s := mHeap_LookupMaybe(&mheap_, unsafe.Pointer(v))
if sp != nil {
*sp = s
}
if s == nil {
if base != nil {
*base = 0
}
if size != nil {
*size = 0
}
return 0
}
p := uintptr(s.start) << _PageShift
if s.sizeclass == 0 {
// Large object.
if base != nil {
*base = p
}
if size != nil {
*size = s.npages << _PageShift
}
return 1
}
n := s.elemsize
if base != nil {
i := (uintptr(v) - uintptr(p)) / n
*base = p + i*n
}
if size != nil {
*size = n
}
return 1
}
//go:nosplit
func purgecachedstats(c *mcache) {
// Protected by either heap or GC lock.
h := &mheap_
memstats.heap_alloc += uint64(c.local_cachealloc)
c.local_cachealloc = 0
if trace.enabled {
traceHeapAlloc()
}
memstats.tinyallocs += uint64(c.local_tinyallocs)
c.local_tinyallocs = 0
memstats.nlookup += uint64(c.local_nlookup)
c.local_nlookup = 0
h.largefree += uint64(c.local_largefree)
c.local_largefree = 0
h.nlargefree += uint64(c.local_nlargefree)
c.local_nlargefree = 0
for i := 0; i < len(c.local_nsmallfree); i++ {
h.nsmallfree[i] += uint64(c.local_nsmallfree[i])
c.local_nsmallfree[i] = 0
}
}
func mallocinit() {
initSizes()
if class_to_size[_TinySizeClass] != _TinySize {
throw("bad TinySizeClass")
}
var p, bitmapSize, spansSize, pSize, limit uintptr
var reserved bool
// limit = runtime.memlimit();
// See https://golang.org/issue/5049
// TODO(rsc): Fix after 1.1.
limit = 0
// Set up the allocation arena, a contiguous area of memory where
// allocated data will be found. The arena begins with a bitmap large
// enough to hold 4 bits per allocated word.
if ptrSize == 8 && (limit == 0 || limit > 1<<30) {
// On a 64-bit machine, allocate from a single contiguous reservation.
// 128 GB (MaxMem) should be big enough for now.
//
// The code will work with the reservation at any address, but ask
// SysReserve to use 0x0000XXc000000000 if possible (XX=00...7f).
// Allocating a 128 GB region takes away 37 bits, and the amd64
// doesn't let us choose the top 17 bits, so that leaves the 11 bits
// in the middle of 0x00c0 for us to choose. Choosing 0x00c0 means
// that the valid memory addresses will begin 0x00c0, 0x00c1, ..., 0x00df.
// In little-endian, that's c0 00, c1 00, ..., df 00. None of those are valid
// UTF-8 sequences, and they are otherwise as far away from
// ff (likely a common byte) as possible. If that fails, we try other 0xXXc0
// addresses. An earlier attempt to use 0x11f8 caused out of memory errors
// on OS X during thread allocations. 0x00c0 causes conflicts with
// AddressSanitizer which reserves all memory up to 0x0100.
// These choices are both for debuggability and to reduce the
// odds of the conservative garbage collector not collecting memory
// because some non-pointer block of memory had a bit pattern
// that matched a memory address.
//
// Actually we reserve 136 GB (because the bitmap ends up being 8 GB)
// but it hardly matters: e0 00 is not valid UTF-8 either.
//
// If this fails we fall back to the 32 bit memory mechanism
arenaSize := round(_MaxMem, _PageSize)
bitmapSize = arenaSize / (ptrSize * 8 / 4)
spansSize = arenaSize / _PageSize * ptrSize
spansSize = round(spansSize, _PageSize)
for i := 0; i <= 0x7f; i++ {
p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
}
if p == 0 {
// On a 32-bit machine, we can't typically get away
// with a giant virtual address space reservation.
// Instead we map the memory information bitmap
// immediately after the data segment, large enough
// to handle another 2GB of mappings (256 MB),
// along with a reservation for an initial arena.
// When that gets used up, we'll start asking the kernel
// for any memory anywhere and hope it's in the 2GB
// following the bitmap (presumably the executable begins
// near the bottom of memory, so we'll have to use up
// most of memory before the kernel resorts to giving out
// memory before the beginning of the text segment).
//
// Alternatively we could reserve 512 MB bitmap, enough
// for 4GB of mappings, and then accept any memory the
// kernel threw at us, but normally that's a waste of 512 MB
// of address space, which is probably too much in a 32-bit world.
// If we fail to allocate, try again with a smaller arena.
// This is necessary on Android L where we share a process
// with ART, which reserves virtual memory aggressively.
arenaSizes := []uintptr{
512 << 20,
256 << 20,
}
for _, arenaSize := range arenaSizes {
bitmapSize = _MaxArena32 / (ptrSize * 8 / 4)
spansSize = _MaxArena32 / _PageSize * ptrSize
if limit > 0 && arenaSize+bitmapSize+spansSize > limit {
bitmapSize = (limit / 9) &^ ((1 << _PageShift) - 1)
arenaSize = bitmapSize * 8
spansSize = arenaSize / _PageSize * ptrSize
}
spansSize = round(spansSize, _PageSize)
// SysReserve treats the address we ask for, end, as a hint,
// not as an absolute requirement. If we ask for the end
// of the data segment but the operating system requires
// a little more space before we can start allocating, it will
// give out a slightly higher pointer. Except QEMU, which
// is buggy, as usual: it won't adjust the pointer upward.
// So adjust it upward a little bit ourselves: 1/4 MB to get
// away from the running binary image and then round up
// to a MB boundary.
p = round(uintptr(unsafe.Pointer(&end))+(1<<18), 1<<20)
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
if p == 0 {
throw("runtime: cannot reserve arena virtual address space")
}
}
// PageSize can be larger than OS definition of page size,
// so SysReserve can give us a PageSize-unaligned pointer.
// To overcome this we ask for PageSize more and round up the pointer.
p1 := round(p, _PageSize)
mheap_.spans = (**mspan)(unsafe.Pointer(p1))
mheap_.bitmap = p1 + spansSize
mheap_.arena_start = p1 + (spansSize + bitmapSize)
mheap_.arena_used = mheap_.arena_start
mheap_.arena_end = p + pSize
mheap_.arena_reserved = reserved
if mheap_.arena_start&(_PageSize-1) != 0 {
println("bad pagesize", hex(p), hex(p1), hex(spansSize), hex(bitmapSize), hex(_PageSize), "start", hex(mheap_.arena_start))
throw("misrounded allocation in mallocinit")
}
// Initialize the rest of the allocator.
mHeap_Init(&mheap_, spansSize)
_g_ := getg()
_g_.m.mcache = allocmcache()
}
// sysReserveHigh reserves space somewhere high in the address space.
// sysReserve doesn't actually reserve the full amount requested on
// 64-bit systems, because of problems with ulimit. Instead it checks
// that it can get the first 64 kB and assumes it can grab the rest as
// needed. This doesn't work well with the "let the kernel pick an address"
// mode, so don't do that. Pick a high address instead.
func sysReserveHigh(n uintptr, reserved *bool) unsafe.Pointer {
if ptrSize == 4 {
return sysReserve(nil, n, reserved)
}
for i := 0; i <= 0x7f; i++ {
p := uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
*reserved = false
p = uintptr(sysReserve(unsafe.Pointer(p), n, reserved))
if p != 0 {
return unsafe.Pointer(p)
}
}
return sysReserve(nil, n, reserved)
}
func mHeap_SysAlloc(h *mheap, n uintptr) unsafe.Pointer {
if n > uintptr(h.arena_end)-uintptr(h.arena_used) {
// We are in 32-bit mode, maybe we didn't use all possible address space yet.
// Reserve some more space.
p_size := round(n+_PageSize, 256<<20)
new_end := h.arena_end + p_size
if new_end <= h.arena_start+_MaxArena32 {
// TODO: It would be bad if part of the arena
// is reserved and part is not.
var reserved bool
p := uintptr(sysReserve((unsafe.Pointer)(h.arena_end), p_size, &reserved))
if p == h.arena_end {
h.arena_end = new_end
h.arena_reserved = reserved
} else if p+p_size <= h.arena_start+_MaxArena32 {
// Keep everything page-aligned.
// Our pages are bigger than hardware pages.
h.arena_end = p + p_size
h.arena_used = p + (-uintptr(p) & (_PageSize - 1))
h.arena_reserved = reserved
} else {
var stat uint64
sysFree((unsafe.Pointer)(p), p_size, &stat)
}
}
}
if n <= uintptr(h.arena_end)-uintptr(h.arena_used) {
// Keep taking from our reservation.
p := h.arena_used
sysMap((unsafe.Pointer)(p), n, h.arena_reserved, &memstats.heap_sys)
h.arena_used += n
mHeap_MapBits(h)
mHeap_MapSpans(h)
if raceenabled {
racemapshadow((unsafe.Pointer)(p), n)
}
if mheap_.shadow_enabled {
sysMap(unsafe.Pointer(p+mheap_.shadow_heap), n, h.shadow_reserved, &memstats.other_sys)
}
if uintptr(p)&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return (unsafe.Pointer)(p)
}
// If using 64-bit, our reservation is all we have.
if uintptr(h.arena_end)-uintptr(h.arena_start) >= _MaxArena32 {
return nil
}
// On 32-bit, once the reservation is gone we can
// try to get memory at a location chosen by the OS
// and hope that it is in the range we allocated bitmap for.
p_size := round(n, _PageSize) + _PageSize
p := uintptr(sysAlloc(p_size, &memstats.heap_sys))
if p == 0 {
return nil
}
if p < h.arena_start || uintptr(p)+p_size-uintptr(h.arena_start) >= _MaxArena32 {
print("runtime: memory allocated by OS (", p, ") not in usable range [", hex(h.arena_start), ",", hex(h.arena_start+_MaxArena32), ")\n")
sysFree((unsafe.Pointer)(p), p_size, &memstats.heap_sys)
return nil
}
p_end := p + p_size
p += -p & (_PageSize - 1)
if uintptr(p)+n > uintptr(h.arena_used) {
h.arena_used = p + n
if p_end > h.arena_end {
h.arena_end = p_end
}
mHeap_MapBits(h)
mHeap_MapSpans(h)
if raceenabled {
racemapshadow((unsafe.Pointer)(p), n)
}
}
if uintptr(p)&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return (unsafe.Pointer)(p)
}
var end struct{}
func largeAlloc(size uintptr, flag uint32) *mspan {
// print("largeAlloc size=", size, "\n")
if size+_PageSize < size {
throw("out of memory")
}
npages := size >> _PageShift
if size&_PageMask != 0 {
npages++
}
s := mHeap_Alloc(&mheap_, npages, 0, true, flag&_FlagNoZero == 0)
if s == nil {
throw("out of memory")
}
s.limit = uintptr(s.start)<<_PageShift + size
heapBitsForSpan(s.base()).initSpan(s.layout())
return s
}

525
src/runtime/malloc2.go
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@ -1,525 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import "unsafe"
// Memory allocator, based on tcmalloc.
// http://goog-perftools.sourceforge.net/doc/tcmalloc.html
// The main allocator works in runs of pages.
// Small allocation sizes (up to and including 32 kB) are
// rounded to one of about 100 size classes, each of which
// has its own free list of objects of exactly that size.
// Any free page of memory can be split into a set of objects
// of one size class, which are then managed using free list
// allocators.
//
// The allocator's data structures are:
//
// FixAlloc: a free-list allocator for fixed-size objects,
// used to manage storage used by the allocator.
// MHeap: the malloc heap, managed at page (4096-byte) granularity.
// MSpan: a run of pages managed by the MHeap.
// MCentral: a shared free list for a given size class.
// MCache: a per-thread (in Go, per-P) cache for small objects.
// MStats: allocation statistics.
//
// Allocating a small object proceeds up a hierarchy of caches:
//
// 1. Round the size up to one of the small size classes
// and look in the corresponding MCache free list.
// If the list is not empty, allocate an object from it.
// This can all be done without acquiring a lock.
//
// 2. If the MCache free list is empty, replenish it by
// taking a bunch of objects from the MCentral free list.
// Moving a bunch amortizes the cost of acquiring the MCentral lock.
//
// 3. If the MCentral free list is empty, replenish it by
// allocating a run of pages from the MHeap and then
// chopping that memory into objects of the given size.
// Allocating many objects amortizes the cost of locking
// the heap.
//
// 4. If the MHeap is empty or has no page runs large enough,
// allocate a new group of pages (at least 1MB) from the
// operating system. Allocating a large run of pages
// amortizes the cost of talking to the operating system.
//
// Freeing a small object proceeds up the same hierarchy:
//
// 1. Look up the size class for the object and add it to
// the MCache free list.
//
// 2. If the MCache free list is too long or the MCache has
// too much memory, return some to the MCentral free lists.
//
// 3. If all the objects in a given span have returned to
// the MCentral list, return that span to the page heap.
//
// 4. If the heap has too much memory, return some to the
// operating system.
//
// TODO(rsc): Step 4 is not implemented.
//
// Allocating and freeing a large object uses the page heap
// directly, bypassing the MCache and MCentral free lists.
//
// The small objects on the MCache and MCentral free lists
// may or may not be zeroed. They are zeroed if and only if
// the second word of the object is zero. A span in the
// page heap is zeroed unless s->needzero is set. When a span
// is allocated to break into small objects, it is zeroed if needed
// and s->needzero is set. There are two main benefits to delaying the
// zeroing this way:
//
// 1. stack frames allocated from the small object lists
// or the page heap can avoid zeroing altogether.
// 2. the cost of zeroing when reusing a small object is
// charged to the mutator, not the garbage collector.
//
// This C code was written with an eye toward translating to Go
// in the future. Methods have the form Type_Method(Type *t, ...).
const (
_PageShift = 13
_PageSize = 1 << _PageShift
_PageMask = _PageSize - 1
)
const (
// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
_64bit = 1 << (^uintptr(0) >> 63) / 2
// Computed constant. The definition of MaxSmallSize and the
// algorithm in msize.c produce some number of different allocation
// size classes. NumSizeClasses is that number. It's needed here
// because there are static arrays of this length; when msize runs its
// size choosing algorithm it double-checks that NumSizeClasses agrees.
_NumSizeClasses = 67
// Tunable constants.
_MaxSmallSize = 32 << 10
// Tiny allocator parameters, see "Tiny allocator" comment in malloc.go.
_TinySize = 16
_TinySizeClass = 2
_FixAllocChunk = 16 << 10 // Chunk size for FixAlloc
_MaxMHeapList = 1 << (20 - _PageShift) // Maximum page length for fixed-size list in MHeap.
_HeapAllocChunk = 1 << 20 // Chunk size for heap growth
// Per-P, per order stack segment cache size.
_StackCacheSize = 32 * 1024
// Number of orders that get caching. Order 0 is FixedStack
// and each successive order is twice as large.
// We want to cache 2KB, 4KB, 8KB, and 16KB stacks. Larger stacks
// will be allocated directly.
// Since FixedStack is different on different systems, we
// must vary NumStackOrders to keep the same maximum cached size.
// OS | FixedStack | NumStackOrders
// -----------------+------------+---------------
// linux/darwin/bsd | 2KB | 4
// windows/32 | 4KB | 3
// windows/64 | 8KB | 2
// plan9 | 4KB | 3
_NumStackOrders = 4 - ptrSize/4*goos_windows - 1*goos_plan9
// Number of bits in page to span calculations (4k pages).
// On Windows 64-bit we limit the arena to 32GB or 35 bits.
// Windows counts memory used by page table into committed memory
// of the process, so we can't reserve too much memory.
// See http://golang.org/issue/5402 and http://golang.org/issue/5236.
// On other 64-bit platforms, we limit the arena to 128GB, or 37 bits.
// On 32-bit, we don't bother limiting anything, so we use the full 32-bit address.
_MHeapMap_TotalBits = (_64bit*goos_windows)*35 + (_64bit*(1-goos_windows))*37 + (1-_64bit)*32
_MHeapMap_Bits = _MHeapMap_TotalBits - _PageShift
_MaxMem = uintptr(1<<_MHeapMap_TotalBits - 1)
// Max number of threads to run garbage collection.
// 2, 3, and 4 are all plausible maximums depending
// on the hardware details of the machine. The garbage
// collector scales well to 32 cpus.
_MaxGcproc = 32
)
// A generic linked list of blocks. (Typically the block is bigger than sizeof(MLink).)
// Since assignments to mlink.next will result in a write barrier being preformed
// this can not be used by some of the internal GC structures. For example when
// the sweeper is placing an unmarked object on the free list it does not want the
// write barrier to be called since that could result in the object being reachable.
type mlink struct {
next *mlink
}
// A gclink is a node in a linked list of blocks, like mlink,
// but it is opaque to the garbage collector.
// The GC does not trace the pointers during collection,
// and the compiler does not emit write barriers for assignments
// of gclinkptr values. Code should store references to gclinks
// as gclinkptr, not as *gclink.
type gclink struct {
next gclinkptr
}
// A gclinkptr is a pointer to a gclink, but it is opaque
// to the garbage collector.
type gclinkptr uintptr
// ptr returns the *gclink form of p.
// The result should be used for accessing fields, not stored
// in other data structures.
func (p gclinkptr) ptr() *gclink {
return (*gclink)(unsafe.Pointer(p))
}
// sysAlloc obtains a large chunk of zeroed memory from the
// operating system, typically on the order of a hundred kilobytes
// or a megabyte.
// NOTE: sysAlloc returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysUnused notifies the operating system that the contents
// of the memory region are no longer needed and can be reused
// for other purposes.
// SysUsed notifies the operating system that the contents
// of the memory region are needed again.
//
// SysFree returns it unconditionally; this is only used if
// an out-of-memory error has been detected midway through
// an allocation. It is okay if SysFree is a no-op.
//
// SysReserve reserves address space without allocating memory.
// If the pointer passed to it is non-nil, the caller wants the
// reservation there, but SysReserve can still choose another
// location if that one is unavailable. On some systems and in some
// cases SysReserve will simply check that the address space is
// available and not actually reserve it. If SysReserve returns
// non-nil, it sets *reserved to true if the address space is
// reserved, false if it has merely been checked.
// NOTE: SysReserve returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysMap maps previously reserved address space for use.
// The reserved argument is true if the address space was really
// reserved, not merely checked.
//
// SysFault marks a (already sysAlloc'd) region to fault
// if accessed. Used only for debugging the runtime.
// FixAlloc is a simple free-list allocator for fixed size objects.
// Malloc uses a FixAlloc wrapped around sysAlloc to manages its
// MCache and MSpan objects.
//
// Memory returned by FixAlloc_Alloc is not zeroed.
// The caller is responsible for locking around FixAlloc calls.
// Callers can keep state in the object but the first word is
// smashed by freeing and reallocating.
type fixalloc struct {
size uintptr
first unsafe.Pointer // go func(unsafe.pointer, unsafe.pointer); f(arg, p) called first time p is returned
arg unsafe.Pointer
list *mlink
chunk *byte
nchunk uint32
inuse uintptr // in-use bytes now
stat *uint64
}
// Statistics.
// Shared with Go: if you edit this structure, also edit type MemStats in mem.go.
type mstats struct {
// General statistics.
alloc uint64 // bytes allocated and still in use
total_alloc uint64 // bytes allocated (even if freed)
sys uint64 // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
nlookup uint64 // number of pointer lookups
nmalloc uint64 // number of mallocs
nfree uint64 // number of frees
// Statistics about malloc heap.
// protected by mheap.lock
heap_alloc uint64 // bytes allocated and still in use
heap_sys uint64 // bytes obtained from system
heap_idle uint64 // bytes in idle spans
heap_inuse uint64 // bytes in non-idle spans
heap_released uint64 // bytes released to the os
heap_objects uint64 // total number of allocated objects
// Statistics about allocation of low-level fixed-size structures.
// Protected by FixAlloc locks.
stacks_inuse uint64 // this number is included in heap_inuse above
stacks_sys uint64 // always 0 in mstats
mspan_inuse uint64 // mspan structures
mspan_sys uint64
mcache_inuse uint64 // mcache structures
mcache_sys uint64
buckhash_sys uint64 // profiling bucket hash table
gc_sys uint64
other_sys uint64
// Statistics about garbage collector.
// Protected by mheap or stopping the world during GC.
next_gc uint64 // next gc (in heap_alloc time)
last_gc uint64 // last gc (in absolute time)
pause_total_ns uint64
pause_ns [256]uint64 // circular buffer of recent gc pause lengths
pause_end [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970)
numgc uint32
enablegc bool
debuggc bool
// Statistics about allocation size classes.
by_size [_NumSizeClasses]struct {
size uint32
nmalloc uint64
nfree uint64
}
tinyallocs uint64 // number of tiny allocations that didn't cause actual allocation; not exported to go directly
}
var memstats mstats
// Size classes. Computed and initialized by InitSizes.
//
// SizeToClass(0 <= n <= MaxSmallSize) returns the size class,
// 1 <= sizeclass < NumSizeClasses, for n.
// Size class 0 is reserved to mean "not small".
//
// class_to_size[i] = largest size in class i
// class_to_allocnpages[i] = number of pages to allocate when
// making new objects in class i
var class_to_size [_NumSizeClasses]int32
var class_to_allocnpages [_NumSizeClasses]int32
var size_to_class8 [1024/8 + 1]int8
var size_to_class128 [(_MaxSmallSize-1024)/128 + 1]int8
type mcachelist struct {
list *mlink
nlist uint32
}
type stackfreelist struct {
list gclinkptr // linked list of free stacks
size uintptr // total size of stacks in list
}
// Per-thread (in Go, per-P) cache for small objects.
// No locking needed because it is per-thread (per-P).
type mcache struct {
// The following members are accessed on every malloc,
// so they are grouped here for better caching.
next_sample int32 // trigger heap sample after allocating this many bytes
local_cachealloc intptr // bytes allocated (or freed) from cache since last lock of heap
// Allocator cache for tiny objects w/o pointers.
// See "Tiny allocator" comment in malloc.go.
tiny unsafe.Pointer
tinyoffset uintptr
local_tinyallocs uintptr // number of tiny allocs not counted in other stats
// The rest is not accessed on every malloc.
alloc [_NumSizeClasses]*mspan // spans to allocate from
stackcache [_NumStackOrders]stackfreelist
sudogcache *sudog
// Local allocator stats, flushed during GC.
local_nlookup uintptr // number of pointer lookups
local_largefree uintptr // bytes freed for large objects (>maxsmallsize)
local_nlargefree uintptr // number of frees for large objects (>maxsmallsize)
local_nsmallfree [_NumSizeClasses]uintptr // number of frees for small objects (<=maxsmallsize)
}
const (
_KindSpecialFinalizer = 1
_KindSpecialProfile = 2
// Note: The finalizer special must be first because if we're freeing
// an object, a finalizer special will cause the freeing operation
// to abort, and we want to keep the other special records around
// if that happens.
)
type special struct {
next *special // linked list in span
offset uint16 // span offset of object
kind byte // kind of special
}
// The described object has a finalizer set for it.
type specialfinalizer struct {
special special
fn *funcval
nret uintptr
fint *_type
ot *ptrtype
}
// The described object is being heap profiled.
type specialprofile struct {
special special
b *bucket
}
// An MSpan is a run of pages.
const (
_MSpanInUse = iota // allocated for garbage collected heap
_MSpanStack // allocated for use by stack allocator
_MSpanFree
_MSpanListHead
_MSpanDead
)
type mspan struct {
next *mspan // in a span linked list
prev *mspan // in a span linked list
start pageID // starting page number
npages uintptr // number of pages in span
freelist gclinkptr // list of free objects
// sweep generation:
// if sweepgen == h->sweepgen - 2, the span needs sweeping
// if sweepgen == h->sweepgen - 1, the span is currently being swept
// if sweepgen == h->sweepgen, the span is swept and ready to use
// h->sweepgen is incremented by 2 after every GC
sweepgen uint32
ref uint16 // capacity - number of objects in freelist
sizeclass uint8 // size class
incache bool // being used by an mcache
state uint8 // mspaninuse etc
needzero uint8 // needs to be zeroed before allocation
elemsize uintptr // computed from sizeclass or from npages
unusedsince int64 // first time spotted by gc in mspanfree state
npreleased uintptr // number of pages released to the os
limit uintptr // end of data in span
speciallock mutex // guards specials list
specials *special // linked list of special records sorted by offset.
}
func (s *mspan) base() uintptr {
return uintptr(s.start << _PageShift)
}
func (s *mspan) layout() (size, n, total uintptr) {
total = s.npages << _PageShift
size = s.elemsize
if size > 0 {
n = total / size
}
return
}
// Every MSpan is in one doubly-linked list,
// either one of the MHeap's free lists or one of the
// MCentral's span lists. We use empty MSpan structures as list heads.
// Central list of free objects of a given size.
type mcentral struct {
lock mutex
sizeclass int32
nonempty mspan // list of spans with a free object
empty mspan // list of spans with no free objects (or cached in an mcache)
}
// Main malloc heap.
// The heap itself is the "free[]" and "large" arrays,
// but all the other global data is here too.
type mheap struct {
lock mutex
free [_MaxMHeapList]mspan // free lists of given length
freelarge mspan // free lists length >= _MaxMHeapList
busy [_MaxMHeapList]mspan // busy lists of large objects of given length
busylarge mspan // busy lists of large objects length >= _MaxMHeapList
allspans **mspan // all spans out there
gcspans **mspan // copy of allspans referenced by gc marker or sweeper
nspan uint32
sweepgen uint32 // sweep generation, see comment in mspan
sweepdone uint32 // all spans are swept
// span lookup
spans **mspan
spans_mapped uintptr
// range of addresses we might see in the heap
bitmap uintptr
bitmap_mapped uintptr
arena_start uintptr
arena_used uintptr
arena_end uintptr
arena_reserved bool
// write barrier shadow data+heap.
// 64-bit systems only, enabled by GODEBUG=wbshadow=1.
shadow_enabled bool // shadow should be updated and checked
shadow_reserved bool // shadow memory is reserved
shadow_heap uintptr // heap-addr + shadow_heap = shadow heap addr
shadow_data uintptr // data-addr + shadow_data = shadow data addr
data_start uintptr // start of shadowed data addresses
data_end uintptr // end of shadowed data addresses
// central free lists for small size classes.
// the padding makes sure that the MCentrals are
// spaced CacheLineSize bytes apart, so that each MCentral.lock
// gets its own cache line.
central [_NumSizeClasses]struct {
mcentral mcentral
pad [_CacheLineSize]byte
}
spanalloc fixalloc // allocator for span*
cachealloc fixalloc // allocator for mcache*
specialfinalizeralloc fixalloc // allocator for specialfinalizer*
specialprofilealloc fixalloc // allocator for specialprofile*
speciallock mutex // lock for sepcial record allocators.
// Malloc stats.
largefree uint64 // bytes freed for large objects (>maxsmallsize)
nlargefree uint64 // number of frees for large objects (>maxsmallsize)
nsmallfree [_NumSizeClasses]uint64 // number of frees for small objects (<=maxsmallsize)
}
var mheap_ mheap
const (
// flags to malloc
_FlagNoScan = 1 << 0 // GC doesn't have to scan object
_FlagNoZero = 1 << 1 // don't zero memory
)
// NOTE: Layout known to queuefinalizer.
type finalizer struct {
fn *funcval // function to call
arg unsafe.Pointer // ptr to object
nret uintptr // bytes of return values from fn
fint *_type // type of first argument of fn
ot *ptrtype // type of ptr to object
}
type finblock struct {
alllink *finblock
next *finblock
cnt int32
_ int32
fin [(_FinBlockSize - 2*ptrSize - 2*4) / unsafe.Sizeof(finalizer{})]finalizer
}
// Information from the compiler about the layout of stack frames.
type bitvector struct {
n int32 // # of bits
bytedata *uint8
}
type stackmap struct {
n int32 // number of bitmaps
nbit int32 // number of bits in each bitmap
bytedata [1]byte // bitmaps, each starting on a 32-bit boundary
}

6
src/runtime/mbitmap.go
View file

@ -82,6 +82,12 @@ const (
typeShift = 2
)
// Information from the compiler about the layout of stack frames.
type bitvector struct {
n int32 // # of bits
bytedata *uint8
}
// addb returns the byte pointer p+n.
//go:nowritebarrier
func addb(p *byte, n uintptr) *byte {

57
src/runtime/mcache.go
View file

@ -2,14 +2,63 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Per-P malloc cache for small objects.
//
// See malloc.h for an overview.
package runtime
import "unsafe"
// Per-thread (in Go, per-P) cache for small objects.
// No locking needed because it is per-thread (per-P).
type mcache struct {
// The following members are accessed on every malloc,
// so they are grouped here for better caching.
next_sample int32 // trigger heap sample after allocating this many bytes
local_cachealloc intptr // bytes allocated (or freed) from cache since last lock of heap
// Allocator cache for tiny objects w/o pointers.
// See "Tiny allocator" comment in malloc.go.
tiny unsafe.Pointer
tinyoffset uintptr
local_tinyallocs uintptr // number of tiny allocs not counted in other stats
// The rest is not accessed on every malloc.
alloc [_NumSizeClasses]*mspan // spans to allocate from
stackcache [_NumStackOrders]stackfreelist
sudogcache *sudog
// Local allocator stats, flushed during GC.
local_nlookup uintptr // number of pointer lookups
local_largefree uintptr // bytes freed for large objects (>maxsmallsize)
local_nlargefree uintptr // number of frees for large objects (>maxsmallsize)
local_nsmallfree [_NumSizeClasses]uintptr // number of frees for small objects (<=maxsmallsize)
}
// A gclink is a node in a linked list of blocks, like mlink,
// but it is opaque to the garbage collector.
// The GC does not trace the pointers during collection,
// and the compiler does not emit write barriers for assignments
// of gclinkptr values. Code should store references to gclinks
// as gclinkptr, not as *gclink.
type gclink struct {
next gclinkptr
}
// A gclinkptr is a pointer to a gclink, but it is opaque
// to the garbage collector.
type gclinkptr uintptr
// ptr returns the *gclink form of p.
// The result should be used for accessing fields, not stored
// in other data structures.
func (p gclinkptr) ptr() *gclink {
return (*gclink)(unsafe.Pointer(p))
}
type stackfreelist struct {
list gclinkptr // linked list of free stacks
size uintptr // total size of stacks in list
}
// dummy MSpan that contains no free objects.
var emptymspan mspan

8
src/runtime/mcentral.go
View file

@ -12,6 +12,14 @@
package runtime
// Central list of free objects of a given size.
type mcentral struct {
lock mutex
sizeclass int32
nonempty mspan // list of spans with a free object
empty mspan // list of spans with no free objects (or cached in an mcache)
}
// Initialize a single central free list.
func mCentral_Init(c *mcentral, sizeclass int32) {
c.sizeclass = sizeclass

114
src/runtime/mem.go
View file

@ -1,114 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import "unsafe"
// Note: the MemStats struct should be kept in sync with
// struct MStats in malloc.h
// A MemStats records statistics about the memory allocator.
type MemStats struct {
// General statistics.
Alloc uint64 // bytes allocated and still in use
TotalAlloc uint64 // bytes allocated (even if freed)
Sys uint64 // bytes obtained from system (sum of XxxSys below)
Lookups uint64 // number of pointer lookups
Mallocs uint64 // number of mallocs
Frees uint64 // number of frees
// Main allocation heap statistics.
HeapAlloc uint64 // bytes allocated and still in use
HeapSys uint64 // bytes obtained from system
HeapIdle uint64 // bytes in idle spans
HeapInuse uint64 // bytes in non-idle span
HeapReleased uint64 // bytes released to the OS
HeapObjects uint64 // total number of allocated objects
// Low-level fixed-size structure allocator statistics.
// Inuse is bytes used now.
// Sys is bytes obtained from system.
StackInuse uint64 // bytes used by stack allocator
StackSys uint64
MSpanInuse uint64 // mspan structures
MSpanSys uint64
MCacheInuse uint64 // mcache structures
MCacheSys uint64
BuckHashSys uint64 // profiling bucket hash table
GCSys uint64 // GC metadata
OtherSys uint64 // other system allocations
// Garbage collector statistics.
NextGC uint64 // next collection will happen when HeapAlloc ≥ this amount
LastGC uint64 // end time of last collection (nanoseconds since 1970)
PauseTotalNs uint64
PauseNs [256]uint64 // circular buffer of recent GC pause durations, most recent at [(NumGC+255)%256]
PauseEnd [256]uint64 // circular buffer of recent GC pause end times
NumGC uint32
EnableGC bool
DebugGC bool
// Per-size allocation statistics.
// 61 is NumSizeClasses in the C code.
BySize [61]struct {
Size uint32
Mallocs uint64
Frees uint64
}
}
// Size of the trailing by_size array differs between Go and C,
// and all data after by_size is local to runtime, not exported.
// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
// sizeof_C_MStats is what C thinks about size of Go struct.
var sizeof_C_MStats = unsafe.Offsetof(memstats.by_size) + 61*unsafe.Sizeof(memstats.by_size[0])
func init() {
var memStats MemStats
if sizeof_C_MStats != unsafe.Sizeof(memStats) {
println(sizeof_C_MStats, unsafe.Sizeof(memStats))
throw("MStats vs MemStatsType size mismatch")
}
}
// ReadMemStats populates m with memory allocator statistics.
func ReadMemStats(m *MemStats) {
// Have to acquire worldsema to stop the world,
// because stoptheworld can only be used by
// one goroutine at a time, and there might be
// a pending garbage collection already calling it.
semacquire(&worldsema, false)
gp := getg()
gp.m.preemptoff = "read mem stats"
systemstack(stoptheworld)
systemstack(func() {
readmemstats_m(m)
})
gp.m.preemptoff = ""
gp.m.locks++
semrelease(&worldsema)
systemstack(starttheworld)
gp.m.locks--
}
//go:linkname runtime_debug_WriteHeapDump runtime/debug.WriteHeapDump
func runtime_debug_WriteHeapDump(fd uintptr) {
semacquire(&worldsema, false)
gp := getg()
gp.m.preemptoff = "write heap dump"
systemstack(stoptheworld)
systemstack(func() {
writeheapdump_m(fd)
})
gp.m.preemptoff = ""
gp.m.locks++
semrelease(&worldsema)
systemstack(starttheworld)
gp.m.locks--
}

17
src/runtime/mfinal.go
View file

@ -8,6 +8,14 @@ package runtime
import "unsafe"
type finblock struct {
alllink *finblock
next *finblock
cnt int32
_ int32
fin [(_FinBlockSize - 2*ptrSize - 2*4) / unsafe.Sizeof(finalizer{})]finalizer
}
var finlock mutex // protects the following variables
var fing *g // goroutine that runs finalizers
var finq *finblock // list of finalizers that are to be executed
@ -17,6 +25,15 @@ var fingwait bool
var fingwake bool
var allfin *finblock // list of all blocks
// NOTE: Layout known to queuefinalizer.
type finalizer struct {
fn *funcval // function to call
arg unsafe.Pointer // ptr to object
nret uintptr // bytes of return values from fn
fint *_type // type of first argument of fn
ot *ptrtype // type of ptr to object
}
var finalizer1 = [...]byte{
// Each Finalizer is 5 words, ptr ptr uintptr ptr ptr.
// Each byte describes 4 words.

28
src/runtime/mfixalloc.go
View file

@ -10,6 +10,34 @@ package runtime
import "unsafe"
// FixAlloc is a simple free-list allocator for fixed size objects.
// Malloc uses a FixAlloc wrapped around sysAlloc to manages its
// MCache and MSpan objects.
//
// Memory returned by FixAlloc_Alloc is not zeroed.
// The caller is responsible for locking around FixAlloc calls.
// Callers can keep state in the object but the first word is
// smashed by freeing and reallocating.
type fixalloc struct {
size uintptr
first unsafe.Pointer // go func(unsafe.pointer, unsafe.pointer); f(arg, p) called first time p is returned
arg unsafe.Pointer
list *mlink
chunk *byte
nchunk uint32
inuse uintptr // in-use bytes now
stat *uint64
}
// A generic linked list of blocks. (Typically the block is bigger than sizeof(MLink).)
// Since assignments to mlink.next will result in a write barrier being preformed
// this can not be used by some of the internal GC structures. For example when
// the sweeper is placing an unmarked object on the free list it does not want the
// write barrier to be called since that could result in the object being reachable.
type mlink struct {
next *mlink
}
// Initialize f to allocate objects of the given size,
// using the allocator to obtain chunks of memory.
func fixAlloc_Init(f *fixalloc, size uintptr, first func(unsafe.Pointer, unsafe.Pointer), arg unsafe.Pointer, stat *uint64) {

1590
src/runtime/mgc.go
View file

File diff suppressed because it is too large Load diff

91
src/runtime/mgc0.go
View file

@ -1,91 +0,0 @@
// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import _ "unsafe" // for go:linkname
//go:linkname runtime_debug_freeOSMemory runtime/debug.freeOSMemory
func runtime_debug_freeOSMemory() {
gogc(2) // force GC and do eager sweep
systemstack(scavenge_m)
}
var poolcleanup func()
//go:linkname sync_runtime_registerPoolCleanup sync.runtime_registerPoolCleanup
func sync_runtime_registerPoolCleanup(f func()) {
poolcleanup = f
}
func clearpools() {
// clear sync.Pools
if poolcleanup != nil {
poolcleanup()
}
for _, p := range &allp {
if p == nil {
break
}
// clear tinyalloc pool
if c := p.mcache; c != nil {
c.tiny = nil
c.tinyoffset = 0
// disconnect cached list before dropping it on the floor,
// so that a dangling ref to one entry does not pin all of them.
var sg, sgnext *sudog
for sg = c.sudogcache; sg != nil; sg = sgnext {
sgnext = sg.next
sg.next = nil
}
c.sudogcache = nil
}
// clear defer pools
for i := range p.deferpool {
// disconnect cached list before dropping it on the floor,
// so that a dangling ref to one entry does not pin all of them.
var d, dlink *_defer
for d = p.deferpool[i]; d != nil; d = dlink {
dlink = d.link
d.link = nil
}
p.deferpool[i] = nil
}
}
}
// backgroundgc is running in a goroutine and does the concurrent GC work.
// bggc holds the state of the backgroundgc.
func backgroundgc() {
bggc.g = getg()
for {
gcwork(0)
lock(&bggc.lock)
bggc.working = 0
goparkunlock(&bggc.lock, "Concurrent GC wait", traceEvGoBlock)
}
}
func bgsweep() {
sweep.g = getg()
for {
for gosweepone() != ^uintptr(0) {
sweep.nbgsweep++
Gosched()
}
lock(&gclock)
if !gosweepdone() {
// This can happen if a GC runs between
// gosweepone returning ^0 above
// and the lock being acquired.
unlock(&gclock)
continue
}
sweep.parked = true
goparkunlock(&gclock, "GC sweep wait", traceEvGoBlock)
}
}

659
src/runtime/mgcmark.go Normal file
View file

@ -0,0 +1,659 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Garbage collector: marking and scanning
package runtime
import "unsafe"
// Scan all of the stacks, greying (or graying if in America) the referents
// but not blackening them since the mark write barrier isn't installed.
//go:nowritebarrier
func gcscan_m() {
_g_ := getg()
// Grab the g that called us and potentially allow rescheduling.
// This allows it to be scanned like other goroutines.
mastergp := _g_.m.curg
casgstatus(mastergp, _Grunning, _Gwaiting)
mastergp.waitreason = "garbage collection scan"
// Span sweeping has been done by finishsweep_m.
// Long term we will want to make this goroutine runnable
// by placing it onto a scanenqueue state and then calling
// runtime·restartg(mastergp) to make it Grunnable.
// At the bottom we will want to return this p back to the scheduler.
// Prepare flag indicating that the scan has not been completed.
lock(&allglock)
local_allglen := allglen
for i := uintptr(0); i < local_allglen; i++ {
gp := allgs[i]
gp.gcworkdone = false // set to true in gcphasework
gp.gcscanvalid = false // stack has not been scanned
}
unlock(&allglock)
work.nwait = 0
work.ndone = 0
work.nproc = 1 // For now do not do this in parallel.
// ackgcphase is not needed since we are not scanning running goroutines.
parforsetup(work.markfor, work.nproc, uint32(_RootCount+local_allglen), false, markroot)
parfordo(work.markfor)
lock(&allglock)
// Check that gc work is done.
for i := uintptr(0); i < local_allglen; i++ {
gp := allgs[i]
if !gp.gcworkdone {
throw("scan missed a g")
}
}
unlock(&allglock)
casgstatus(mastergp, _Gwaiting, _Grunning)
// Let the g that called us continue to run.
}
// ptrmask for an allocation containing a single pointer.
var oneptr = [...]uint8{typePointer}
//go:nowritebarrier
func markroot(desc *parfor, i uint32) {
var gcw gcWorkProducer
gcw.initFromCache()
// Note: if you add a case here, please also update heapdump.c:dumproots.
switch i {
case _RootData:
scanblock(uintptr(unsafe.Pointer(&data)), uintptr(unsafe.Pointer(&edata))-uintptr(unsafe.Pointer(&data)), gcdatamask.bytedata, &gcw)
case _RootBss:
scanblock(uintptr(unsafe.Pointer(&bss)), uintptr(unsafe.Pointer(&ebss))-uintptr(unsafe.Pointer(&bss)), gcbssmask.bytedata, &gcw)
case _RootFinalizers:
for fb := allfin; fb != nil; fb = fb.alllink {
scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), uintptr(fb.cnt)*unsafe.Sizeof(fb.fin[0]), &finptrmask[0], &gcw)
}
case _RootSpans:
// mark MSpan.specials
sg := mheap_.sweepgen
for spanidx := uint32(0); spanidx < uint32(len(work.spans)); spanidx++ {
s := work.spans[spanidx]
if s.state != mSpanInUse {
continue
}
if !checkmarkphase && s.sweepgen != sg {
// sweepgen was updated (+2) during non-checkmark GC pass
print("sweep ", s.sweepgen, " ", sg, "\n")
throw("gc: unswept span")
}
for sp := s.specials; sp != nil; sp = sp.next {
if sp.kind != _KindSpecialFinalizer {
continue
}
// don't mark finalized object, but scan it so we
// retain everything it points to.
spf := (*specialfinalizer)(unsafe.Pointer(sp))
// A finalizer can be set for an inner byte of an object, find object beginning.
p := uintptr(s.start<<_PageShift) + uintptr(spf.special.offset)/s.elemsize*s.elemsize
if gcphase != _GCscan {
scanblock(p, s.elemsize, nil, &gcw) // scanned during mark phase
}
scanblock(uintptr(unsafe.Pointer(&spf.fn)), ptrSize, &oneptr[0], &gcw)
}
}
case _RootFlushCaches:
if gcphase != _GCscan { // Do not flush mcaches during GCscan phase.
flushallmcaches()
}
default:
// the rest is scanning goroutine stacks
if uintptr(i-_RootCount) >= allglen {
throw("markroot: bad index")
}
gp := allgs[i-_RootCount]
// remember when we've first observed the G blocked
// needed only to output in traceback
status := readgstatus(gp) // We are not in a scan state
if (status == _Gwaiting || status == _Gsyscall) && gp.waitsince == 0 {
gp.waitsince = work.tstart
}
// Shrink a stack if not much of it is being used but not in the scan phase.
if gcphase == _GCmarktermination {
// Shrink during STW GCmarktermination phase thus avoiding
// complications introduced by shrinking during
// non-STW phases.
shrinkstack(gp)
}
if readgstatus(gp) == _Gdead {
gp.gcworkdone = true
} else {
gp.gcworkdone = false
}
restart := stopg(gp)
// goroutine will scan its own stack when it stops running.
// Wait until it has.
for readgstatus(gp) == _Grunning && !gp.gcworkdone {
}
// scanstack(gp) is done as part of gcphasework
// But to make sure we finished we need to make sure that
// the stack traps have all responded so drop into
// this while loop until they respond.
for !gp.gcworkdone {
status = readgstatus(gp)
if status == _Gdead {
gp.gcworkdone = true // scan is a noop
break
}
if status == _Gwaiting || status == _Grunnable {
restart = stopg(gp)
}
}
if restart {
restartg(gp)
}
}
gcw.dispose()
}
// gchelpwork does a small bounded amount of gc work. The purpose is to
// shorten the time (as measured by allocations) spent doing a concurrent GC.
// The number of mutator calls is roughly propotional to the number of allocations
// made by that mutator. This slows down the allocation while speeding up the GC.
//go:nowritebarrier
func gchelpwork() {
switch gcphase {
default:
throw("gcphasework in bad gcphase")
case _GCoff, _GCquiesce, _GCstw:
// No work.
case _GCsweep:
// We could help by calling sweepone to sweep a single span.
// _ = sweepone()
case _GCscan:
// scan the stack, mark the objects, put pointers in work buffers
// hanging off the P where this is being run.
// scanstack(gp)
case _GCmark:
// Get a full work buffer and empty it.
// drain your own currentwbuf first in the hopes that it will
// be more cache friendly.
var gcw gcWork
gcw.initFromCache()
const n = len(workbuf{}.obj)
gcDrainN(&gcw, n) // drain upto one buffer's worth of objects
gcw.dispose()
case _GCmarktermination:
// We should never be here since the world is stopped.
// All available mark work will be emptied before returning.
throw("gcphasework in bad gcphase")
}
}
// The gp has been moved to a GC safepoint. GC phase specific
// work is done here.
//go:nowritebarrier
func gcphasework(gp *g) {
switch gcphase {
default:
throw("gcphasework in bad gcphase")
case _GCoff, _GCquiesce, _GCstw, _GCsweep:
// No work.
case _GCscan:
// scan the stack, mark the objects, put pointers in work buffers
// hanging off the P where this is being run.
// Indicate that the scan is valid until the goroutine runs again
scanstack(gp)
case _GCmark:
// No work.
case _GCmarktermination:
scanstack(gp)
// All available mark work will be emptied before returning.
}
gp.gcworkdone = true
}
//go:nowritebarrier
func scanstack(gp *g) {
if gp.gcscanvalid {
return
}
if readgstatus(gp)&_Gscan == 0 {
print("runtime:scanstack: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", hex(readgstatus(gp)), "\n")
throw("scanstack - bad status")
}
switch readgstatus(gp) &^ _Gscan {
default:
print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
throw("mark - bad status")
case _Gdead:
return
case _Grunning:
print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
throw("scanstack: goroutine not stopped")
case _Grunnable, _Gsyscall, _Gwaiting:
// ok
}
if gp == getg() {
throw("can't scan our own stack")
}
mp := gp.m
if mp != nil && mp.helpgc != 0 {
throw("can't scan gchelper stack")
}
var gcw gcWorkProducer
gcw.initFromCache()
scanframe := func(frame *stkframe, unused unsafe.Pointer) bool {
// Pick up gcw as free variable so gentraceback and friends can
// keep the same signature.
scanframeworker(frame, unused, &gcw)
return true
}
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0)
tracebackdefers(gp, scanframe, nil)
gcw.disposeToCache()
gp.gcscanvalid = true
}
// Scan a stack frame: local variables and function arguments/results.
//go:nowritebarrier
func scanframeworker(frame *stkframe, unused unsafe.Pointer, gcw *gcWorkProducer) {
f := frame.fn
targetpc := frame.continpc
if targetpc == 0 {
// Frame is dead.
return
}
if _DebugGC > 1 {
print("scanframe ", funcname(f), "\n")
}
if targetpc != f.entry {
targetpc--
}
pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc)
if pcdata == -1 {
// We do not have a valid pcdata value but there might be a
// stackmap for this function. It is likely that we are looking
// at the function prologue, assume so and hope for the best.
pcdata = 0
}
// Scan local variables if stack frame has been allocated.
size := frame.varp - frame.sp
var minsize uintptr
if thechar != '6' && thechar != '8' {
minsize = ptrSize
} else {
minsize = 0
}
if size > minsize {
stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps))
if stkmap == nil || stkmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped locals ", hex(frame.varp-size), "+", hex(size), "\n")
throw("missing stackmap")
}
// Locals bitmap information, scan just the pointers in locals.
if pcdata < 0 || pcdata >= stkmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " locals stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("scanframe: bad symbol table")
}
bv := stackmapdata(stkmap, pcdata)
size = (uintptr(bv.n) / typeBitsWidth) * ptrSize
scanblock(frame.varp-size, size, bv.bytedata, gcw)
}
// Scan arguments.
if frame.arglen > 0 {
var bv bitvector
if frame.argmap != nil {
bv = *frame.argmap
} else {
stkmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps))
if stkmap == nil || stkmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped args ", hex(frame.argp), "+", hex(frame.arglen), "\n")
throw("missing stackmap")
}
if pcdata < 0 || pcdata >= stkmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " args stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("scanframe: bad symbol table")
}
bv = stackmapdata(stkmap, pcdata)
}
scanblock(frame.argp, uintptr(bv.n)/typeBitsWidth*ptrSize, bv.bytedata, gcw)
}
}
// gcDrain scans objects in work buffers (starting with wbuf), blackening grey
// objects until all work buffers have been drained.
//go:nowritebarrier
func gcDrain(gcw *gcWork) {
if gcphase != _GCmark && gcphase != _GCmarktermination {
throw("scanblock phase incorrect")
}
for {
// If another proc wants a pointer, give it some.
if work.nwait > 0 && work.full == 0 {
gcw.balance()
}
b := gcw.get()
if b == 0 {
// work barrier reached
break
}
// If the current wbuf is filled by the scan a new wbuf might be
// returned that could possibly hold only a single object. This
// could result in each iteration draining only a single object
// out of the wbuf passed in + a single object placed
// into an empty wbuf in scanobject so there could be
// a performance hit as we keep fetching fresh wbufs.
scanobject(b, 0, nil, &gcw.gcWorkProducer)
}
checknocurrentwbuf()
}
// gcDrainN scans n objects, blackening grey objects.
//go:nowritebarrier
func gcDrainN(gcw *gcWork, n int) {
checknocurrentwbuf()
for i := 0; i < n; i++ {
// This might be a good place to add prefetch code...
// if(wbuf.nobj > 4) {
// PREFETCH(wbuf->obj[wbuf.nobj - 3];
// }
b := gcw.tryGet()
if b == 0 {
return
}
scanobject(b, 0, nil, &gcw.gcWorkProducer)
}
}
// scanblock scans b as scanobject would.
// If the gcphase is GCscan, scanblock performs additional checks.
//go:nowritebarrier
func scanblock(b0, n0 uintptr, ptrmask *uint8, gcw *gcWorkProducer) {
// Use local copies of original parameters, so that a stack trace
// due to one of the throws below shows the original block
// base and extent.
b := b0
n := n0
// ptrmask can have 2 possible values:
// 1. nil - obtain pointer mask from GC bitmap.
// 2. pointer to a compact mask (for stacks and data).
scanobject(b, n, ptrmask, gcw)
if gcphase == _GCscan {
if inheap(b) && ptrmask == nil {
// b is in heap, we are in GCscan so there should be a ptrmask.
throw("scanblock: In GCscan phase and inheap is true.")
}
}
}
// Scan the object b of size n, adding pointers to wbuf.
// Return possibly new wbuf to use.
// If ptrmask != nil, it specifies where pointers are in b.
// If ptrmask == nil, the GC bitmap should be consulted.
// In this case, n may be an overestimate of the size; the GC bitmap
// must also be used to make sure the scan stops at the end of b.
//go:nowritebarrier
func scanobject(b, n uintptr, ptrmask *uint8, gcw *gcWorkProducer) {
arena_start := mheap_.arena_start
arena_used := mheap_.arena_used
// Find bits of the beginning of the object.
var hbits heapBits
if ptrmask == nil {
b, hbits = heapBitsForObject(b)
if b == 0 {
return
}
if n == 0 {
n = mheap_.arena_used - b
}
}
for i := uintptr(0); i < n; i += ptrSize {
// Find bits for this word.
var bits uintptr
if ptrmask != nil {
// dense mask (stack or data)
bits = (uintptr(*(*byte)(add(unsafe.Pointer(ptrmask), (i/ptrSize)/4))) >> (((i / ptrSize) % 4) * typeBitsWidth)) & typeMask
} else {
// Check if we have reached end of span.
// n is an overestimate of the size of the object.
if (b+i)%_PageSize == 0 && h_spans[(b-arena_start)>>_PageShift] != h_spans[(b+i-arena_start)>>_PageShift] {
break
}
bits = uintptr(hbits.typeBits())
if i > 0 && (hbits.isBoundary() || bits == typeDead) {
break // reached beginning of the next object
}
hbits = hbits.next()
}
if bits <= typeScalar { // typeScalar, typeDead, typeScalarMarked
continue
}
if bits&typePointer != typePointer {
print("gc checkmarkphase=", checkmarkphase, " b=", hex(b), " ptrmask=", ptrmask, "\n")
throw("unexpected garbage collection bits")
}
obj := *(*uintptr)(unsafe.Pointer(b + i))
// At this point we have extracted the next potential pointer.
// Check if it points into heap.
if obj == 0 || obj < arena_start || obj >= arena_used {
continue
}
if mheap_.shadow_enabled && debug.wbshadow >= 2 && debug.gccheckmark > 0 && checkmarkphase {
checkwbshadow((*uintptr)(unsafe.Pointer(b + i)))
}
// Mark the object.
if obj, hbits := heapBitsForObject(obj); obj != 0 {
greyobject(obj, b, i, hbits, gcw)
}
}
}
// Shade the object if it isn't already.
// The object is not nil and known to be in the heap.
//go:nowritebarrier
func shade(b uintptr) {
if !inheap(b) {
throw("shade: passed an address not in the heap")
}
if obj, hbits := heapBitsForObject(b); obj != 0 {
// TODO: this would be a great place to put a check to see
// if we are harvesting and if we are then we should
// figure out why there is a call to shade when the
// harvester thinks we are in a STW.
// if atomicload(&harvestingwbufs) == uint32(1) {
// // Throw here to discover write barriers
// // being executed during a STW.
// throw("shade during harvest")
// }
var gcw gcWorkProducer
greyobject(obj, 0, 0, hbits, &gcw)
// This is part of the write barrier so put the wbuf back.
if gcphase == _GCmarktermination {
gcw.dispose()
} else {
// If we added any pointers to the gcw, then
// currentwbuf must be nil because 1)
// greyobject got its wbuf from currentwbuf
// and 2) shade runs on the systemstack, so
// we're still on the same M. If either of
// these becomes no longer true, we need to
// rethink this.
gcw.disposeToCache()
}
}
}
// obj is the start of an object with mark mbits.
// If it isn't already marked, mark it and enqueue into workbuf.
// Return possibly new workbuf to use.
// base and off are for debugging only and could be removed.
//go:nowritebarrier
func greyobject(obj, base, off uintptr, hbits heapBits, gcw *gcWorkProducer) {
// obj should be start of allocation, and so must be at least pointer-aligned.
if obj&(ptrSize-1) != 0 {
throw("greyobject: obj not pointer-aligned")
}
if checkmarkphase {
if !hbits.isMarked() {
print("runtime:greyobject: checkmarks finds unexpected unmarked object obj=", hex(obj), "\n")
print("runtime: found obj at *(", hex(base), "+", hex(off), ")\n")
// Dump the source (base) object
kb := base >> _PageShift
xb := kb
xb -= mheap_.arena_start >> _PageShift
sb := h_spans[xb]
printlock()
print("runtime:greyobject Span: base=", hex(base), " kb=", hex(kb))
if sb == nil {
print(" sb=nil\n")
} else {
print(" sb.start*_PageSize=", hex(sb.start*_PageSize), " sb.limit=", hex(sb.limit), " sb.sizeclass=", sb.sizeclass, " sb.elemsize=", sb.elemsize, "\n")
// base is (a pointer to) the source object holding the reference to object. Create a pointer to each of the fields
// fields in base and print them out as hex values.
for i := 0; i < int(sb.elemsize/ptrSize); i++ {
print(" *(base+", i*ptrSize, ") = ", hex(*(*uintptr)(unsafe.Pointer(base + uintptr(i)*ptrSize))), "\n")
}
}
// Dump the object
k := obj >> _PageShift
x := k
x -= mheap_.arena_start >> _PageShift
s := h_spans[x]
print("runtime:greyobject Span: obj=", hex(obj), " k=", hex(k))
if s == nil {
print(" s=nil\n")
} else {
print(" s.start=", hex(s.start*_PageSize), " s.limit=", hex(s.limit), " s.sizeclass=", s.sizeclass, " s.elemsize=", s.elemsize, "\n")
// NOTE(rsc): This code is using s.sizeclass as an approximation of the
// number of pointer-sized words in an object. Perhaps not what was intended.
for i := 0; i < int(s.sizeclass); i++ {
print(" *(obj+", i*ptrSize, ") = ", hex(*(*uintptr)(unsafe.Pointer(obj + uintptr(i)*ptrSize))), "\n")
}
}
throw("checkmark found unmarked object")
}
if !hbits.isCheckmarked() {
return
}
hbits.setCheckmarked()
if !hbits.isCheckmarked() {
throw("setCheckmarked and isCheckmarked disagree")
}
} else {
// If marked we have nothing to do.
if hbits.isMarked() {
return
}
// Each byte of GC bitmap holds info for two words.
// Might be racing with other updates, so use atomic update always.
// We used to be clever here and use a non-atomic update in certain
// cases, but it's not worth the risk.
hbits.setMarked()
}
if !checkmarkphase && hbits.typeBits() == typeDead {
return // noscan object
}
// Queue the obj for scanning. The PREFETCH(obj) logic has been removed but
// seems like a nice optimization that can be added back in.
// There needs to be time between the PREFETCH and the use.
// Previously we put the obj in an 8 element buffer that is drained at a rate
// to give the PREFETCH time to do its work.
// Use of PREFETCHNTA might be more appropriate than PREFETCH
gcw.put(obj)
}
// When in GCmarkterminate phase we allocate black.
//go:nowritebarrier
func gcmarknewobject_m(obj uintptr) {
if gcphase != _GCmarktermination {
throw("marking new object while not in mark termination phase")
}
if checkmarkphase { // The world should be stopped so this should not happen.
throw("gcmarknewobject called while doing checkmark")
}
heapBitsForAddr(obj).setMarked()
}
// Checkmarking
// To help debug the concurrent GC we remark with the world
// stopped ensuring that any object encountered has their normal
// mark bit set. To do this we use an orthogonal bit
// pattern to indicate the object is marked. The following pattern
// uses the upper two bits in the object's bounday nibble.
// 01: scalar not marked
// 10: pointer not marked
// 11: pointer marked
// 00: scalar marked
// Xoring with 01 will flip the pattern from marked to unmarked and vica versa.
// The higher bit is 1 for pointers and 0 for scalars, whether the object
// is marked or not.
// The first nibble no longer holds the typeDead pattern indicating that the
// there are no more pointers in the object. This information is held
// in the second nibble.
// When marking an object if the bool checkmarkphase is true one uses the above
// encoding, otherwise one uses the bitMarked bit in the lower two bits
// of the nibble.
var checkmarkphase = false
//go:nowritebarrier
func initCheckmarks() {
for _, s := range work.spans {
if s.state == _MSpanInUse {
heapBitsForSpan(s.base()).initCheckmarkSpan(s.layout())
}
}
}
func clearCheckmarks() {
for _, s := range work.spans {
if s.state == _MSpanInUse {
heapBitsForSpan(s.base()).clearCheckmarkSpan(s.layout())
}
}
}

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src/runtime/mgcsweep.go Normal file
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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Garbage collector: sweeping
package runtime
import "unsafe"
var sweep sweepdata
// State of background sweep.
// Protected by gclock.
type sweepdata struct {
g *g
parked bool
started bool
spanidx uint32 // background sweeper position
nbgsweep uint32
npausesweep uint32
}
var gclock mutex
//go:nowritebarrier
func finishsweep_m() {
// The world is stopped so we should be able to complete the sweeps
// quickly.
for sweepone() != ^uintptr(0) {
sweep.npausesweep++
}
// There may be some other spans being swept concurrently that
// we need to wait for. If finishsweep_m is done with the world stopped
// this code is not required.
sg := mheap_.sweepgen
for _, s := range work.spans {
if s.sweepgen != sg && s.state == _MSpanInUse {
mSpan_EnsureSwept(s)
}
}
}
func bgsweep() {
sweep.g = getg()
for {
for gosweepone() != ^uintptr(0) {
sweep.nbgsweep++
Gosched()
}
lock(&gclock)
if !gosweepdone() {
// This can happen if a GC runs between
// gosweepone returning ^0 above
// and the lock being acquired.
unlock(&gclock)
continue
}
sweep.parked = true
goparkunlock(&gclock, "GC sweep wait", traceEvGoBlock)
}
}
// sweeps one span
// returns number of pages returned to heap, or ^uintptr(0) if there is nothing to sweep
//go:nowritebarrier
func sweepone() uintptr {
_g_ := getg()
// increment locks to ensure that the goroutine is not preempted
// in the middle of sweep thus leaving the span in an inconsistent state for next GC
_g_.m.locks++
sg := mheap_.sweepgen
for {
idx := xadd(&sweep.spanidx, 1) - 1
if idx >= uint32(len(work.spans)) {
mheap_.sweepdone = 1
_g_.m.locks--
return ^uintptr(0)
}
s := work.spans[idx]
if s.state != mSpanInUse {
s.sweepgen = sg
continue
}
if s.sweepgen != sg-2 || !cas(&s.sweepgen, sg-2, sg-1) {
continue
}
npages := s.npages
if !mSpan_Sweep(s, false) {
npages = 0
}
_g_.m.locks--
return npages
}
}
//go:nowritebarrier
func gosweepone() uintptr {
var ret uintptr
systemstack(func() {
ret = sweepone()
})
return ret
}
//go:nowritebarrier
func gosweepdone() bool {
return mheap_.sweepdone != 0
}
// Returns only when span s has been swept.
//go:nowritebarrier
func mSpan_EnsureSwept(s *mspan) {
// Caller must disable preemption.
// Otherwise when this function returns the span can become unswept again
// (if GC is triggered on another goroutine).
_g_ := getg()
if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
throw("MSpan_EnsureSwept: m is not locked")
}
sg := mheap_.sweepgen
if atomicload(&s.sweepgen) == sg {
return
}
// The caller must be sure that the span is a MSpanInUse span.
if cas(&s.sweepgen, sg-2, sg-1) {
mSpan_Sweep(s, false)
return
}
// unfortunate condition, and we don't have efficient means to wait
for atomicload(&s.sweepgen) != sg {
osyield()
}
}
// Sweep frees or collects finalizers for blocks not marked in the mark phase.
// It clears the mark bits in preparation for the next GC round.
// Returns true if the span was returned to heap.
// If preserve=true, don't return it to heap nor relink in MCentral lists;
// caller takes care of it.
//TODO go:nowritebarrier
func mSpan_Sweep(s *mspan, preserve bool) bool {
if checkmarkphase {
throw("MSpan_Sweep: checkmark only runs in STW and after the sweep")
}
// It's critical that we enter this function with preemption disabled,
// GC must not start while we are in the middle of this function.
_g_ := getg()
if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
throw("MSpan_Sweep: m is not locked")
}
sweepgen := mheap_.sweepgen
if s.state != mSpanInUse || s.sweepgen != sweepgen-1 {
print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n")
throw("MSpan_Sweep: bad span state")
}
if trace.enabled {
traceGCSweepStart()
}
cl := s.sizeclass
size := s.elemsize
res := false
nfree := 0
var head, end gclinkptr
c := _g_.m.mcache
sweepgenset := false
// Mark any free objects in this span so we don't collect them.
for link := s.freelist; link.ptr() != nil; link = link.ptr().next {
heapBitsForAddr(uintptr(link)).setMarkedNonAtomic()
}
// Unlink & free special records for any objects we're about to free.
specialp := &s.specials
special := *specialp
for special != nil {
// A finalizer can be set for an inner byte of an object, find object beginning.
p := uintptr(s.start<<_PageShift) + uintptr(special.offset)/size*size
hbits := heapBitsForAddr(p)
if !hbits.isMarked() {
// Find the exact byte for which the special was setup
// (as opposed to object beginning).
p := uintptr(s.start<<_PageShift) + uintptr(special.offset)
// about to free object: splice out special record
y := special
special = special.next
*specialp = special
if !freespecial(y, unsafe.Pointer(p), size, false) {
// stop freeing of object if it has a finalizer
hbits.setMarkedNonAtomic()
}
} else {
// object is still live: keep special record
specialp = &special.next
special = *specialp
}
}
// Sweep through n objects of given size starting at p.
// This thread owns the span now, so it can manipulate
// the block bitmap without atomic operations.
size, n, _ := s.layout()
heapBitsSweepSpan(s.base(), size, n, func(p uintptr) {
// At this point we know that we are looking at garbage object
// that needs to be collected.
if debug.allocfreetrace != 0 {
tracefree(unsafe.Pointer(p), size)
}
// Reset to allocated+noscan.
if cl == 0 {
// Free large span.
if preserve {
throw("can't preserve large span")
}
heapBitsForSpan(p).clearSpan(s.layout())
s.needzero = 1
// important to set sweepgen before returning it to heap
atomicstore(&s.sweepgen, sweepgen)
sweepgenset = true
// NOTE(rsc,dvyukov): The original implementation of efence
// in CL 22060046 used SysFree instead of SysFault, so that
// the operating system would eventually give the memory
// back to us again, so that an efence program could run
// longer without running out of memory. Unfortunately,
// calling SysFree here without any kind of adjustment of the
// heap data structures means that when the memory does
// come back to us, we have the wrong metadata for it, either in
// the MSpan structures or in the garbage collection bitmap.
// Using SysFault here means that the program will run out of
// memory fairly quickly in efence mode, but at least it won't
// have mysterious crashes due to confused memory reuse.
// It should be possible to switch back to SysFree if we also
// implement and then call some kind of MHeap_DeleteSpan.
if debug.efence > 0 {
s.limit = 0 // prevent mlookup from finding this span
sysFault(unsafe.Pointer(p), size)
} else {
mHeap_Free(&mheap_, s, 1)
}
c.local_nlargefree++
c.local_largefree += size
reduction := int64(size) * int64(gcpercent+100) / 100
if int64(memstats.next_gc)-reduction > int64(heapminimum) {
xadd64(&memstats.next_gc, -reduction)
} else {
atomicstore64(&memstats.next_gc, heapminimum)
}
res = true
} else {
// Free small object.
if size > 2*ptrSize {
*(*uintptr)(unsafe.Pointer(p + ptrSize)) = uintptrMask & 0xdeaddeaddeaddead // mark as "needs to be zeroed"
} else if size > ptrSize {
*(*uintptr)(unsafe.Pointer(p + ptrSize)) = 0
}
if head.ptr() == nil {
head = gclinkptr(p)
} else {
end.ptr().next = gclinkptr(p)
}
end = gclinkptr(p)
end.ptr().next = gclinkptr(0x0bade5)
nfree++
}
})
// We need to set s.sweepgen = h.sweepgen only when all blocks are swept,
// because of the potential for a concurrent free/SetFinalizer.
// But we need to set it before we make the span available for allocation
// (return it to heap or mcentral), because allocation code assumes that a
// span is already swept if available for allocation.
if !sweepgenset && nfree == 0 {
// The span must be in our exclusive ownership until we update sweepgen,
// check for potential races.
if s.state != mSpanInUse || s.sweepgen != sweepgen-1 {
print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n")
throw("MSpan_Sweep: bad span state after sweep")
}
atomicstore(&s.sweepgen, sweepgen)
}
if nfree > 0 {
c.local_nsmallfree[cl] += uintptr(nfree)
c.local_cachealloc -= intptr(uintptr(nfree) * size)
reduction := int64(nfree) * int64(size) * int64(gcpercent+100) / 100
if int64(memstats.next_gc)-reduction > int64(heapminimum) {
xadd64(&memstats.next_gc, -reduction)
} else {
atomicstore64(&memstats.next_gc, heapminimum)
}
res = mCentral_FreeSpan(&mheap_.central[cl].mcentral, s, int32(nfree), head, end, preserve)
// MCentral_FreeSpan updates sweepgen
}
if trace.enabled {
traceGCSweepDone()
traceNextGC()
}
return res
}

214
src/runtime/mheap.go
View file

@ -4,7 +4,72 @@
// Page heap.
//
// See malloc.h for overview.
// See malloc.go for overview.
package runtime
import "unsafe"
// Main malloc heap.
// The heap itself is the "free[]" and "large" arrays,
// but all the other global data is here too.
type mheap struct {
lock mutex
free [_MaxMHeapList]mspan // free lists of given length
freelarge mspan // free lists length >= _MaxMHeapList
busy [_MaxMHeapList]mspan // busy lists of large objects of given length
busylarge mspan // busy lists of large objects length >= _MaxMHeapList
allspans **mspan // all spans out there
gcspans **mspan // copy of allspans referenced by gc marker or sweeper
nspan uint32
sweepgen uint32 // sweep generation, see comment in mspan
sweepdone uint32 // all spans are swept
// span lookup
spans **mspan
spans_mapped uintptr
// range of addresses we might see in the heap
bitmap uintptr
bitmap_mapped uintptr
arena_start uintptr
arena_used uintptr
arena_end uintptr
arena_reserved bool
// write barrier shadow data+heap.
// 64-bit systems only, enabled by GODEBUG=wbshadow=1.
shadow_enabled bool // shadow should be updated and checked
shadow_reserved bool // shadow memory is reserved
shadow_heap uintptr // heap-addr + shadow_heap = shadow heap addr
shadow_data uintptr // data-addr + shadow_data = shadow data addr
data_start uintptr // start of shadowed data addresses
data_end uintptr // end of shadowed data addresses
// central free lists for small size classes.
// the padding makes sure that the MCentrals are
// spaced CacheLineSize bytes apart, so that each MCentral.lock
// gets its own cache line.
central [_NumSizeClasses]struct {
mcentral mcentral
pad [_CacheLineSize]byte
}
spanalloc fixalloc // allocator for span*
cachealloc fixalloc // allocator for mcache*
specialfinalizeralloc fixalloc // allocator for specialfinalizer*
specialprofilealloc fixalloc // allocator for specialprofile*
speciallock mutex // lock for sepcial record allocators.
// Malloc stats.
largefree uint64 // bytes freed for large objects (>maxsmallsize)
nlargefree uint64 // number of frees for large objects (>maxsmallsize)
nsmallfree [_NumSizeClasses]uint64 // number of frees for small objects (<=maxsmallsize)
}
var mheap_ mheap
// An MSpan is a run of pages.
//
// When a MSpan is in the heap free list, state == MSpanFree
// and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
@ -12,9 +77,55 @@
// When a MSpan is allocated, state == MSpanInUse or MSpanStack
// and heapmap(i) == span for all s->start <= i < s->start+s->npages.
package runtime
// Every MSpan is in one doubly-linked list,
// either one of the MHeap's free lists or one of the
// MCentral's span lists. We use empty MSpan structures as list heads.
import "unsafe"
const (
_MSpanInUse = iota // allocated for garbage collected heap
_MSpanStack // allocated for use by stack allocator
_MSpanFree
_MSpanListHead
_MSpanDead
)
type mspan struct {
next *mspan // in a span linked list
prev *mspan // in a span linked list
start pageID // starting page number
npages uintptr // number of pages in span
freelist gclinkptr // list of free objects
// sweep generation:
// if sweepgen == h->sweepgen - 2, the span needs sweeping
// if sweepgen == h->sweepgen - 1, the span is currently being swept
// if sweepgen == h->sweepgen, the span is swept and ready to use
// h->sweepgen is incremented by 2 after every GC
sweepgen uint32
ref uint16 // capacity - number of objects in freelist
sizeclass uint8 // size class
incache bool // being used by an mcache
state uint8 // mspaninuse etc
needzero uint8 // needs to be zeroed before allocation
elemsize uintptr // computed from sizeclass or from npages
unusedsince int64 // first time spotted by gc in mspanfree state
npreleased uintptr // number of pages released to the os
limit uintptr // end of data in span
speciallock mutex // guards specials list
specials *special // linked list of special records sorted by offset.
}
func (s *mspan) base() uintptr {
return uintptr(s.start << _PageShift)
}
func (s *mspan) layout() (size, n, total uintptr) {
total = s.npages << _PageShift
size = s.elemsize
if size > 0 {
n = total / size
}
return
}
var h_allspans []*mspan // TODO: make this h.allspans once mheap can be defined in Go
var h_spans []*mspan // TODO: make this h.spans once mheap can be defined in Go
@ -50,6 +161,73 @@ func recordspan(vh unsafe.Pointer, p unsafe.Pointer) {
h.nspan = uint32(len(h_allspans))
}
// inheap reports whether b is a pointer into a (potentially dead) heap object.
// It returns false for pointers into stack spans.
//go:nowritebarrier
func inheap(b uintptr) bool {
if b == 0 || b < mheap_.arena_start || b >= mheap_.arena_used {
return false
}
// Not a beginning of a block, consult span table to find the block beginning.
k := b >> _PageShift
x := k
x -= mheap_.arena_start >> _PageShift
s := h_spans[x]
if s == nil || pageID(k) < s.start || b >= s.limit || s.state != mSpanInUse {
return false
}
return true
}
func mlookup(v uintptr, base *uintptr, size *uintptr, sp **mspan) int32 {
_g_ := getg()
_g_.m.mcache.local_nlookup++
if ptrSize == 4 && _g_.m.mcache.local_nlookup >= 1<<30 {
// purge cache stats to prevent overflow
lock(&mheap_.lock)
purgecachedstats(_g_.m.mcache)
unlock(&mheap_.lock)
}
s := mHeap_LookupMaybe(&mheap_, unsafe.Pointer(v))
if sp != nil {
*sp = s
}
if s == nil {
if base != nil {
*base = 0
}
if size != nil {
*size = 0
}
return 0
}
p := uintptr(s.start) << _PageShift
if s.sizeclass == 0 {
// Large object.
if base != nil {
*base = p
}
if size != nil {
*size = s.npages << _PageShift
}
return 1
}
n := s.elemsize
if base != nil {
i := (uintptr(v) - uintptr(p)) / n
*base = p + i*n
}
if size != nil {
*size = n
}
return 1
}
// Initialize the heap.
func mHeap_Init(h *mheap, spans_size uintptr) {
fixAlloc_Init(&h.spanalloc, unsafe.Sizeof(mspan{}), recordspan, unsafe.Pointer(h), &memstats.mspan_sys)
@ -635,6 +813,21 @@ func mSpanList_InsertBack(list *mspan, span *mspan) {
span.prev.next = span
}
const (
_KindSpecialFinalizer = 1
_KindSpecialProfile = 2
// Note: The finalizer special must be first because if we're freeing
// an object, a finalizer special will cause the freeing operation
// to abort, and we want to keep the other special records around
// if that happens.
)
type special struct {
next *special // linked list in span
offset uint16 // span offset of object
kind byte // kind of special
}
// Adds the special record s to the list of special records for
// the object p. All fields of s should be filled in except for
// offset & next, which this routine will fill in.
@ -723,6 +916,15 @@ func removespecial(p unsafe.Pointer, kind uint8) *special {
return nil
}
// The described object has a finalizer set for it.
type specialfinalizer struct {
special special
fn *funcval
nret uintptr
fint *_type
ot *ptrtype
}
// Adds a finalizer to the object p. Returns true if it succeeded.
func addfinalizer(p unsafe.Pointer, f *funcval, nret uintptr, fint *_type, ot *ptrtype) bool {
lock(&mheap_.speciallock)
@ -755,6 +957,12 @@ func removefinalizer(p unsafe.Pointer) {
unlock(&mheap_.speciallock)
}
// The described object is being heap profiled.
type specialprofile struct {
special special
b *bucket
}
// Set the heap profile bucket associated with addr to b.
func setprofilebucket(p unsafe.Pointer, b *bucket) {
lock(&mheap_.speciallock)

18
src/runtime/msize.go
View file

@ -27,8 +27,15 @@
package runtime
//var class_to_size [_NumSizeClasses]int32
//var class_to_allocnpages [_NumSizeClasses]int32
// Size classes. Computed and initialized by InitSizes.
//
// SizeToClass(0 <= n <= MaxSmallSize) returns the size class,
// 1 <= sizeclass < NumSizeClasses, for n.
// Size class 0 is reserved to mean "not small".
//
// class_to_size[i] = largest size in class i
// class_to_allocnpages[i] = number of pages to allocate when
// making new objects in class i
// The SizeToClass lookup is implemented using two arrays,
// one mapping sizes <= 1024 to their class and one mapping
@ -38,8 +45,11 @@ package runtime
// are 128-aligned, so the second array is indexed by the
// size divided by 128 (rounded up). The arrays are filled in
// by InitSizes.
//var size_to_class8 [1024/8 + 1]int8
//var size_to_class128 [(_MaxSmallSize-1024)/128 + 1]int8
var class_to_size [_NumSizeClasses]int32
var class_to_allocnpages [_NumSizeClasses]int32
var size_to_class8 [1024/8 + 1]int8
var size_to_class128 [(_MaxSmallSize-1024)/128 + 1]int8
func sizeToClass(size int32) int32 {
if size > _MaxSmallSize {

340
src/runtime/mstats.go Normal file
View file

@ -0,0 +1,340 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Memory statistics
package runtime
import "unsafe"
// Statistics.
// Shared with Go: if you edit this structure, also edit type MemStats in mem.go.
type mstats struct {
// General statistics.
alloc uint64 // bytes allocated and still in use
total_alloc uint64 // bytes allocated (even if freed)
sys uint64 // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
nlookup uint64 // number of pointer lookups
nmalloc uint64 // number of mallocs
nfree uint64 // number of frees
// Statistics about malloc heap.
// protected by mheap.lock
heap_alloc uint64 // bytes allocated and still in use
heap_sys uint64 // bytes obtained from system
heap_idle uint64 // bytes in idle spans
heap_inuse uint64 // bytes in non-idle spans
heap_released uint64 // bytes released to the os
heap_objects uint64 // total number of allocated objects
// Statistics about allocation of low-level fixed-size structures.
// Protected by FixAlloc locks.
stacks_inuse uint64 // this number is included in heap_inuse above
stacks_sys uint64 // always 0 in mstats
mspan_inuse uint64 // mspan structures
mspan_sys uint64
mcache_inuse uint64 // mcache structures
mcache_sys uint64
buckhash_sys uint64 // profiling bucket hash table
gc_sys uint64
other_sys uint64
// Statistics about garbage collector.
// Protected by mheap or stopping the world during GC.
next_gc uint64 // next gc (in heap_alloc time)
last_gc uint64 // last gc (in absolute time)
pause_total_ns uint64
pause_ns [256]uint64 // circular buffer of recent gc pause lengths
pause_end [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970)
numgc uint32
enablegc bool
debuggc bool
// Statistics about allocation size classes.
by_size [_NumSizeClasses]struct {
size uint32
nmalloc uint64
nfree uint64
}
tinyallocs uint64 // number of tiny allocations that didn't cause actual allocation; not exported to go directly
}
var memstats mstats
// Note: the MemStats struct should be kept in sync with
// struct MStats in malloc.h
// A MemStats records statistics about the memory allocator.
type MemStats struct {
// General statistics.
Alloc uint64 // bytes allocated and still in use
TotalAlloc uint64 // bytes allocated (even if freed)
Sys uint64 // bytes obtained from system (sum of XxxSys below)
Lookups uint64 // number of pointer lookups
Mallocs uint64 // number of mallocs
Frees uint64 // number of frees
// Main allocation heap statistics.
HeapAlloc uint64 // bytes allocated and still in use
HeapSys uint64 // bytes obtained from system
HeapIdle uint64 // bytes in idle spans
HeapInuse uint64 // bytes in non-idle span
HeapReleased uint64 // bytes released to the OS
HeapObjects uint64 // total number of allocated objects
// Low-level fixed-size structure allocator statistics.
// Inuse is bytes used now.
// Sys is bytes obtained from system.
StackInuse uint64 // bytes used by stack allocator
StackSys uint64
MSpanInuse uint64 // mspan structures
MSpanSys uint64
MCacheInuse uint64 // mcache structures
MCacheSys uint64
BuckHashSys uint64 // profiling bucket hash table
GCSys uint64 // GC metadata
OtherSys uint64 // other system allocations
// Garbage collector statistics.
NextGC uint64 // next collection will happen when HeapAlloc ≥ this amount
LastGC uint64 // end time of last collection (nanoseconds since 1970)
PauseTotalNs uint64
PauseNs [256]uint64 // circular buffer of recent GC pause durations, most recent at [(NumGC+255)%256]
PauseEnd [256]uint64 // circular buffer of recent GC pause end times
NumGC uint32
EnableGC bool
DebugGC bool
// Per-size allocation statistics.
// 61 is NumSizeClasses in the C code.
BySize [61]struct {
Size uint32
Mallocs uint64
Frees uint64
}
}
// Size of the trailing by_size array differs between Go and C,
// and all data after by_size is local to runtime, not exported.
// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
// sizeof_C_MStats is what C thinks about size of Go struct.
var sizeof_C_MStats = unsafe.Offsetof(memstats.by_size) + 61*unsafe.Sizeof(memstats.by_size[0])
func init() {
var memStats MemStats
if sizeof_C_MStats != unsafe.Sizeof(memStats) {
println(sizeof_C_MStats, unsafe.Sizeof(memStats))
throw("MStats vs MemStatsType size mismatch")
}
}
// ReadMemStats populates m with memory allocator statistics.
func ReadMemStats(m *MemStats) {
// Have to acquire worldsema to stop the world,
// because stoptheworld can only be used by
// one goroutine at a time, and there might be
// a pending garbage collection already calling it.
semacquire(&worldsema, false)
gp := getg()
gp.m.preemptoff = "read mem stats"
systemstack(stoptheworld)
systemstack(func() {
readmemstats_m(m)
})
gp.m.preemptoff = ""
gp.m.locks++
semrelease(&worldsema)
systemstack(starttheworld)
gp.m.locks--
}
func readmemstats_m(stats *MemStats) {
updatememstats(nil)
// Size of the trailing by_size array differs between Go and C,
// NumSizeClasses was changed, but we can not change Go struct because of backward compatibility.
memmove(unsafe.Pointer(stats), unsafe.Pointer(&memstats), sizeof_C_MStats)
// Stack numbers are part of the heap numbers, separate those out for user consumption
stats.StackSys = stats.StackInuse
stats.HeapInuse -= stats.StackInuse
stats.HeapSys -= stats.StackInuse
}
//go:linkname readGCStats runtime/debug.readGCStats
func readGCStats(pauses *[]uint64) {
systemstack(func() {
readGCStats_m(pauses)
})
}
func readGCStats_m(pauses *[]uint64) {
p := *pauses
// Calling code in runtime/debug should make the slice large enough.
if cap(p) < len(memstats.pause_ns)+3 {
throw("short slice passed to readGCStats")
}
// Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns.
lock(&mheap_.lock)
n := memstats.numgc
if n > uint32(len(memstats.pause_ns)) {
n = uint32(len(memstats.pause_ns))
}
// The pause buffer is circular. The most recent pause is at
// pause_ns[(numgc-1)%len(pause_ns)], and then backward
// from there to go back farther in time. We deliver the times
// most recent first (in p[0]).
p = p[:cap(p)]
for i := uint32(0); i < n; i++ {
j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns))
p[i] = memstats.pause_ns[j]
p[n+i] = memstats.pause_end[j]
}
p[n+n] = memstats.last_gc
p[n+n+1] = uint64(memstats.numgc)
p[n+n+2] = memstats.pause_total_ns
unlock(&mheap_.lock)
*pauses = p[:n+n+3]
}
//go:nowritebarrier
func updatememstats(stats *gcstats) {
if stats != nil {
*stats = gcstats{}
}
for mp := allm; mp != nil; mp = mp.alllink {
if stats != nil {
src := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(&mp.gcstats))
dst := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(stats))
for i, v := range src {
dst[i] += v
}
mp.gcstats = gcstats{}
}
}
memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse)
memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse)
memstats.sys = memstats.heap_sys + memstats.stacks_sys + memstats.mspan_sys +
memstats.mcache_sys + memstats.buckhash_sys + memstats.gc_sys + memstats.other_sys
// Calculate memory allocator stats.
// During program execution we only count number of frees and amount of freed memory.
// Current number of alive object in the heap and amount of alive heap memory
// are calculated by scanning all spans.
// Total number of mallocs is calculated as number of frees plus number of alive objects.
// Similarly, total amount of allocated memory is calculated as amount of freed memory
// plus amount of alive heap memory.
memstats.alloc = 0
memstats.total_alloc = 0
memstats.nmalloc = 0
memstats.nfree = 0
for i := 0; i < len(memstats.by_size); i++ {
memstats.by_size[i].nmalloc = 0
memstats.by_size[i].nfree = 0
}
// Flush MCache's to MCentral.
systemstack(flushallmcaches)
// Aggregate local stats.
cachestats()
// Scan all spans and count number of alive objects.
lock(&mheap_.lock)
for i := uint32(0); i < mheap_.nspan; i++ {
s := h_allspans[i]
if s.state != mSpanInUse {
continue
}
if s.sizeclass == 0 {
memstats.nmalloc++
memstats.alloc += uint64(s.elemsize)
} else {
memstats.nmalloc += uint64(s.ref)
memstats.by_size[s.sizeclass].nmalloc += uint64(s.ref)
memstats.alloc += uint64(s.ref) * uint64(s.elemsize)
}
}
unlock(&mheap_.lock)
// Aggregate by size class.
smallfree := uint64(0)
memstats.nfree = mheap_.nlargefree
for i := 0; i < len(memstats.by_size); i++ {
memstats.nfree += mheap_.nsmallfree[i]
memstats.by_size[i].nfree = mheap_.nsmallfree[i]
memstats.by_size[i].nmalloc += mheap_.nsmallfree[i]
smallfree += uint64(mheap_.nsmallfree[i]) * uint64(class_to_size[i])
}
memstats.nfree += memstats.tinyallocs
memstats.nmalloc += memstats.nfree
// Calculate derived stats.
memstats.total_alloc = uint64(memstats.alloc) + uint64(mheap_.largefree) + smallfree
memstats.heap_alloc = memstats.alloc
memstats.heap_objects = memstats.nmalloc - memstats.nfree
}
//go:nowritebarrier
func cachestats() {
for i := 0; ; i++ {
p := allp[i]
if p == nil {
break
}
c := p.mcache
if c == nil {
continue
}
purgecachedstats(c)
}
}
//go:nowritebarrier
func flushallmcaches() {
for i := 0; ; i++ {
p := allp[i]
if p == nil {
break
}
c := p.mcache
if c == nil {
continue
}
mCache_ReleaseAll(c)
stackcache_clear(c)
}
}
//go:nosplit
func purgecachedstats(c *mcache) {
// Protected by either heap or GC lock.
h := &mheap_
memstats.heap_alloc += uint64(c.local_cachealloc)
c.local_cachealloc = 0
if trace.enabled {
traceHeapAlloc()
}
memstats.tinyallocs += uint64(c.local_tinyallocs)
c.local_tinyallocs = 0
memstats.nlookup += uint64(c.local_nlookup)
c.local_nlookup = 0
h.largefree += uint64(c.local_largefree)
c.local_largefree = 0
h.nlargefree += uint64(c.local_nlargefree)
c.local_nlargefree = 0
for i := 0; i < len(c.local_nsmallfree); i++ {
h.nsmallfree[i] += uint64(c.local_nsmallfree[i])
c.local_nsmallfree[i] = 0
}
}

15
src/runtime/proc1.go
View file

@ -528,6 +528,21 @@ func quiesce(mastergp *g) {
mcall(mquiesce)
}
// Holding worldsema grants an M the right to try to stop the world.
// The procedure is:
//
// semacquire(&worldsema);
// m.preemptoff = "reason";
// stoptheworld();
//
// ... do stuff ...
//
// m.preemptoff = "";
// semrelease(&worldsema);
// starttheworld();
//
var worldsema uint32 = 1
// This is used by the GC as well as the routines that do stack dumps. In the case
// of GC all the routines can be reliably stopped. This is not always the case
// when the system is in panic or being exited.

10
src/runtime/stubs.go
View file

@ -239,3 +239,13 @@ func prefetcht0(addr uintptr)
func prefetcht1(addr uintptr)
func prefetcht2(addr uintptr)
func prefetchnta(addr uintptr)
func unixnanotime() int64 {
sec, nsec := time_now()
return sec*1e9 + int64(nsec)
}
// round n up to a multiple of a. a must be a power of 2.
func round(n, a uintptr) uintptr {
return (n + a - 1) &^ (a - 1)
}

14
src/runtime/symtab.go
View file

@ -299,3 +299,17 @@ func readvarint(p []byte) (newp []byte, val uint32) {
}
return p, v
}
type stackmap struct {
n int32 // number of bitmaps
nbit int32 // number of bits in each bitmap
bytedata [1]byte // bitmaps, each starting on a 32-bit boundary
}
//go:nowritebarrier
func stackmapdata(stkmap *stackmap, n int32) bitvector {
if n < 0 || n >= stkmap.n {
throw("stackmapdata: index out of range")
}
return bitvector{stkmap.nbit, (*byte)(add(unsafe.Pointer(&stkmap.bytedata), uintptr(n*((stkmap.nbit+31)/32*4))))}
}