runtime: keep objects in free lists marked as allocated.
Restore https://golang.org/cl/41040043 after GC rewrite.
Original description:
On the plus side, we don't need to change the bits on malloc and free.
On the downside, we need to mark objects in the free lists during GC.
But the free lists are small at GC time, so it should be a net win.
benchmark old ns/op new ns/op delta
BenchmarkMalloc8 21.9 20.4 -6.85%
BenchmarkMalloc16 31.1 29.6 -4.82%
LGTM=khr
R=khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/122280043
diff --git a/src/pkg/runtime/malloc.go b/src/pkg/runtime/malloc.go
index 71c0a4e..76c06f3 100644
--- a/src/pkg/runtime/malloc.go
+++ b/src/pkg/runtime/malloc.go
@@ -41,11 +41,9 @@
bitsDead = 0
bitsPointer = 2
- bitMiddle = 0
- bitBoundary = 1
- bitAllocated = 2
- bitMarked = 3
- bitMask = bitMiddle | bitBoundary | bitAllocated | bitMarked
+ bitBoundary = 1
+ bitMarked = 2
+ bitMask = bitBoundary | bitMarked
)
// All zero-sized allocations return a pointer to this byte.
@@ -185,110 +183,108 @@
size = uintptr(s.elemsize)
}
- // From here till marked label marking the object as allocated
- // and storing type info in the GC bitmap.
- 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
- if debugMalloc && (((*xbits)>>shift)&bitMask) != bitBoundary {
- gothrow("bad bits in markallocated")
+ if flags&flagNoScan != 0 {
+ // All objects are pre-marked as noscan.
+ goto marked
}
- var ti, te uintptr
- var ptrmask *uint8
- if flags&flagNoScan != 0 {
- // bitsDead in the first quadruple means don't scan.
- if size == ptrSize {
- *xbits = (*xbits & ^((bitBoundary | bitPtrMask) << shift)) | ((bitAllocated + (bitsDead << 2)) << shift)
- } else {
- xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
- *xbitsb = bitAllocated + (bitsDead << 2)
+ // From here till marked label marking the object as allocated
+ // and storing type info in the GC bitmap.
+ {
+ 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
+ if debugMalloc && ((*xbits>>shift)&(bitMask|bitPtrMask)) != bitBoundary {
+ println("runtime: bits =", (*xbits>>shift)&(bitMask|bitPtrMask))
+ gothrow("bad bits in markallocated")
}
- goto marked
- }
- if size == ptrSize {
- // It's one word and it has pointers, it must be a pointer.
- *xbits = (*xbits & ^((bitBoundary | bitPtrMask) << shift)) | ((bitAllocated | (bitsPointer << 2)) << shift)
- goto marked
- }
- if typ != nil && (uintptr(typ.gc[0])|uintptr(typ.gc[1])) != 0 && uintptr(typ.size) > ptrSize {
- if typ.kind&kindGCProg != 0 {
- nptr := (uintptr(typ.size) + ptrSize - 1) / ptrSize
- masksize := nptr
- if masksize%2 != 0 {
- masksize *= 2 // repeated
+
+ var ti, te uintptr
+ var ptrmask *uint8
+ if size == ptrSize {
+ // It's one word and it has pointers, it must be a pointer.
+ *xbits |= (bitsPointer << 2) << shift
+ goto marked
+ }
+ if typ != nil && (uintptr(typ.gc[0])|uintptr(typ.gc[1])) != 0 && uintptr(typ.size) > ptrSize {
+ if typ.kind&kindGCProg != 0 {
+ nptr := (uintptr(typ.size) + ptrSize - 1) / ptrSize
+ masksize := nptr
+ if masksize%2 != 0 {
+ masksize *= 2 // repeated
+ }
+ masksize = masksize * pointersPerByte / 8 // 4 bits per word
+ masksize++ // unroll flag in the beginning
+ if masksize > maxGCMask && typ.gc[1] != 0 {
+ // If the mask is too large, unroll the program directly
+ // into the GC bitmap. It's 7 times slower than copying
+ // from the pre-unrolled mask, but saves 1/16 of type size
+ // memory for the mask.
+ mp.ptrarg[0] = x
+ mp.ptrarg[1] = unsafe.Pointer(typ)
+ mp.scalararg[0] = uint(size)
+ mp.scalararg[1] = uint(size0)
+ onM(&unrollgcproginplace_m)
+ goto marked
+ }
+ ptrmask = (*uint8)(unsafe.Pointer(uintptr(typ.gc[0])))
+ // Check whether the program is already unrolled.
+ if uintptr(goatomicloadp(unsafe.Pointer(ptrmask)))&0xff == 0 {
+ mp.ptrarg[0] = unsafe.Pointer(typ)
+ onM(&unrollgcprog_m)
+ }
+ ptrmask = (*uint8)(add(unsafe.Pointer(ptrmask), 1)) // skip the unroll flag byte
+ } else {
+ ptrmask = (*uint8)(unsafe.Pointer(&typ.gc[0])) // embed mask
}
- masksize = masksize * pointersPerByte / 8 // 4 bits per word
- masksize++ // unroll flag in the beginning
- if masksize > maxGCMask && typ.gc[1] != 0 {
- // If the mask is too large, unroll the program directly
- // into the GC bitmap. It's 7 times slower than copying
- // from the pre-unrolled mask, but saves 1/16 of type size
- // memory for the mask.
- mp.ptrarg[0] = x
- mp.ptrarg[1] = unsafe.Pointer(typ)
- mp.scalararg[0] = uint(size)
- mp.scalararg[1] = uint(size0)
- onM(&unrollgcproginplace_m)
+ if size == 2*ptrSize {
+ xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
+ *xbitsb = *ptrmask | bitBoundary
goto marked
}
- ptrmask = (*uint8)(unsafe.Pointer(uintptr(typ.gc[0])))
- // Check whether the program is already unrolled.
- if uintptr(goatomicloadp(unsafe.Pointer(ptrmask)))&0xff == 0 {
- mp.ptrarg[0] = unsafe.Pointer(typ)
- onM(&unrollgcprog_m)
+ te = uintptr(typ.size) / ptrSize
+ // If the type occupies odd number of words, its mask is repeated.
+ if te%2 == 0 {
+ te /= 2
}
- ptrmask = (*uint8)(add(unsafe.Pointer(ptrmask), 1)) // skip the unroll flag byte
- } else {
- ptrmask = (*uint8)(unsafe.Pointer(&typ.gc[0])) // embed mask
}
if size == 2*ptrSize {
xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
- *xbitsb = *ptrmask | bitAllocated
+ *xbitsb = (bitsPointer << 2) | (bitsPointer << 6) | bitBoundary
goto marked
}
- te = uintptr(typ.size) / ptrSize
- // If the type occupies odd number of words, its mask is repeated.
- if te%2 == 0 {
- te /= 2
- }
- }
- if size == 2*ptrSize {
- xbitsb := (*uint8)(add(unsafe.Pointer(xbits), shift/8))
- *xbitsb = (bitsPointer << 2) | (bitsPointer << 6) | bitAllocated
- goto marked
- }
- // Copy pointer bitmask into the bitmap.
- for i := uintptr(0); i < size0; i += 2 * ptrSize {
- v := uint8((bitsPointer << 2) | (bitsPointer << 6))
- if ptrmask != nil {
- v = *(*uint8)(add(unsafe.Pointer(ptrmask), ti))
- ti++
- if ti == te {
- ti = 0
+ // Copy pointer bitmask into the bitmap.
+ for i := uintptr(0); i < size0; i += 2 * ptrSize {
+ v := uint8((bitsPointer << 2) | (bitsPointer << 6))
+ if ptrmask != nil {
+ v = *(*uint8)(add(unsafe.Pointer(ptrmask), ti))
+ ti++
+ if ti == te {
+ ti = 0
+ }
}
- }
- if i == 0 {
- v |= bitAllocated
- }
- if i+ptrSize == size0 {
- v &= ^uint8(bitPtrMask << 4)
- }
+ if i == 0 {
+ v |= bitBoundary
+ }
+ if i+ptrSize == size0 {
+ 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
- }
- 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
+ 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
+ }
+ 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
+ }
}
marked:
mp.mallocing = 0
