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[dev.garbage] runtime: remove heapBitsSweepSpan

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Prior to this CL the sweep phase was responsible for locating
all objects that were about to be freed and calling a function
to process the object. This was done by the function
heapBitsSweepSpan. Part of processing included calls to
tracefree and msanfree as well as counting how many objects
were freed.

The calls to tracefree and msanfree have been moved into the
gcmalloc routine and called when the object is about to be
reallocated. The counting of free objects has been optimized
using an array based popcnt algorithm and if all the objects
in a span are free then span is freed.

Similarly the code to locate the next free object has been
optimized to use an array based ctz (count trailing zero).
Various hot paths in the allocation logic have been optimized.

At this point the garbage benchmark is within 3% of the 1.6
release.

Change-Id: I00643c442e2ada1685c010c3447e4ea8537d2dfa
Reviewed-on: https://go-review.googlesource.com/20201
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Rick Hudson 2016-03-02 12:15:02 -05:00
parent 4093481523
commit 8dda1c4c08
4 changed files with 187 additions and 174 deletions
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12
src/runtime/mheap.go
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@ -137,6 +137,9 @@ type mspan struct {
//
// Object n starts at address n*elemsize + (start << pageShift).
freeindex uintptr
// TODO: Look up nelems from sizeclass and remove this field if it
// helps performance.
nelems uintptr // number of object in the span.
// Cache of the allocBits at freeindex. allocCache is shifted
// such that the lowest bit corresponds to the bit freeindex.
@ -147,9 +150,6 @@ type mspan struct {
allocCache uint64
allocBits *[maxObjsPerSpan / 8]uint8
gcmarkBits *[maxObjsPerSpan / 8]uint8
nelems uintptr // number of object in the span.
// TODO(rlh) consider moving some of these fields into seperate arrays.
// Put another way is an array of structs a better idea than a struct of arrays.
// allocBits and gcmarkBits currently point to either markbits1
// or markbits2. At the end of a GC cycle allocBits and
@ -753,6 +753,12 @@ func (h *mheap) freeSpan(s *mspan, acct int32) {
mp.mcache.local_scan = 0
memstats.tinyallocs += uint64(mp.mcache.local_tinyallocs)
mp.mcache.local_tinyallocs = 0
if msanenabled {
// Tell msan that this entire span is no longer in use.
base := unsafe.Pointer(s.base())
bytes := s.npages << _PageShift
msanfree(base, bytes)
}
if acct != 0 {
memstats.heap_objects--
}