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runtime: simplify sweep allocation counting

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Currently sweep counts the number of allocated objects, computes the
number of free objects from that, then re-computes the number of
allocated objects from that. Simplify and clean this up by skipping
these intermediate steps.

Change-Id: I3ed98e371eb54bbcab7c8530466c4ab5fde35f0a
Reviewed-on: https://go-review.googlesource.com/34935
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-12-22 18:00:18 -07:00
parent f1ba75f8c5
commit b50b728587
2 changed files with 7 additions and 9 deletions
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8
src/runtime/mbitmap.go
View File

@ -823,10 +823,10 @@ var oneBitCount = [256]uint8{
4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7,
5, 6, 6, 7, 6, 7, 7, 8} 5, 6, 6, 7, 6, 7, 7, 8}
// countFree runs through the mark bits in a span and counts the number of free objects // countAlloc returns the number of objects allocated in span s by
// in the span. // scanning the allocation bitmap.
// TODO:(rlh) Use popcount intrinsic. // TODO:(rlh) Use popcount intrinsic.
func (s *mspan) countFree() int { func (s *mspan) countAlloc() int {
count := 0 count := 0
maxIndex := s.nelems / 8 maxIndex := s.nelems / 8
for i := uintptr(0); i < maxIndex; i++ { for i := uintptr(0); i < maxIndex; i++ {
@ -839,7 +839,7 @@ func (s *mspan) countFree() int {
bits := mrkBits & mask bits := mrkBits & mask
count += int(oneBitCount[bits]) count += int(oneBitCount[bits])
} }
return int(s.nelems) - count return count
} }
// heapBitsSetType records that the new allocation [x, x+size) // heapBitsSetType records that the new allocation [x, x+size)

8
src/runtime/mgcsweep.go
View File

@ -186,7 +186,6 @@ func (s *mspan) sweep(preserve bool) bool {
cl := s.sizeclass cl := s.sizeclass
size := s.elemsize size := s.elemsize
res := false res := false
nfree := 0
c := _g_.m.mcache c := _g_.m.mcache
freeToHeap := false freeToHeap := false
@ -276,15 +275,14 @@ func (s *mspan) sweep(preserve bool) bool {
} }
// Count the number of free objects in this span. // Count the number of free objects in this span.
nfree = s.countFree() nalloc := uint16(s.countAlloc())
if cl == 0 && nfree != 0 { if cl == 0 && nalloc == 0 {
s.needzero = 1 s.needzero = 1
freeToHeap = true freeToHeap = true
} }
nalloc := uint16(s.nelems) - uint16(nfree)
nfreed := s.allocCount - nalloc nfreed := s.allocCount - nalloc
if nalloc > s.allocCount { if nalloc > s.allocCount {
print("runtime: nelems=", s.nelems, " nfree=", nfree, " nalloc=", nalloc, " previous allocCount=", s.allocCount, " nfreed=", nfreed, "\n") print("runtime: nelems=", s.nelems, " nalloc=", nalloc, " previous allocCount=", s.allocCount, " nfreed=", nfreed, "\n")
throw("sweep increased allocation count") throw("sweep increased allocation count")
} }