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runtime: make the GC bitmap a byte array

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Half the code in the garbage collector accesses the bitmap
as an array of bytes instead of as an array of uintptrs.
This is tricky to do correctly in a portable fashion,
it breaks on big-endian systems.
Make the bitmap a byte array.
Simplifies markallocated, scanblock and span sweep along the way,
as we don't need to recalculate bitmap position for each word.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/125250043
This commit is contained in:
Dmitriy Vyukov 2014-08-19 17:38:00 +04:00
parent fb44fb6cb7
commit ff3fa1b32d
8 changed files with 168 additions and 125 deletions
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22
src/pkg/runtime/malloc.go
View file

@ -22,8 +22,8 @@ const (
pageSize = 1 << pageShift
pageMask = pageSize - 1
wordsPerBitmapWord = ptrSize * 8 / 4
gcBits = 4
wordsPerBitmapByte = 8 / gcBits
bitsPerPointer = 2
bitsMask = 1<<bitsPerPointer - 1
pointersPerByte = 8 / bitsPerPointer
@ -211,8 +211,8 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
{
arena_start := uintptr(unsafe.Pointer(mheap_.arena_start))
off := (uintptr(x) - arena_start) / ptrSize
xbits := (*uintptr)(unsafe.Pointer(arena_start - off/wordsPerBitmapWord*ptrSize - ptrSize))
shift := (off % wordsPerBitmapWord) * gcBits
xbits := (*uint8)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
shift := (off % wordsPerBitmapByte) * gcBits
if debugMalloc && ((*xbits>>shift)&(bitMask|bitPtrMask)) != bitBoundary {
println("runtime: bits =", (*xbits>>shift)&(bitMask|bitPtrMask))
gothrow("bad bits in markallocated")
@ -260,8 +260,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
ptrmask = (*uint8)(unsafe.Pointer(&typ.gc[0])) // embed mask
}
if size == 2*ptrSize {
xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
*xbitsb = *ptrmask | bitBoundary
*xbits = *ptrmask | bitBoundary
goto marked
}
te = uintptr(typ.size) / ptrSize
@ -283,19 +282,12 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
v &^= uint8(bitPtrMask << 4)
}
off := (uintptr(x) + i - arena_start) / ptrSize
xbits := (*uintptr)(unsafe.Pointer(arena_start - off/wordsPerBitmapWord*ptrSize - ptrSize))
shift := (off % wordsPerBitmapWord) * gcBits
xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
*xbitsb = v
*xbits = v
xbits = (*byte)(add(unsafe.Pointer(xbits), ^uintptr(0)))
}
if size0%(2*ptrSize) == 0 && size0 < size {
// Mark the word after last object's word as bitsDead.
off := (uintptr(x) + size0 - arena_start) / ptrSize
xbits := (*uintptr)(unsafe.Pointer(arena_start - off/wordsPerBitmapWord*ptrSize - ptrSize))
shift := (off % wordsPerBitmapWord) * gcBits
xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
*xbitsb = bitsDead << 2
*xbits = bitsDead << 2
}
}
marked: