From 4591f49938aedbbac7a24225047984479abe72b8 Mon Sep 17 00:00:00 2001 From: Hans Date: Mon, 2 Aug 2021 05:43:29 +0000 Subject: [PATCH] runtime: do not alloc never used tail bytes in fixalloc Currently, the '_FixAllocChunk % fixalloc.size' tail bytes will never be used when allocing from persistentalloc. Wasted bytes on darwin/amd64: _FixAllocChunk % mheap_.spanalloc.size = 64 _FixAllocChunk % mheap_.cachealloc.size = 784 _FixAllocChunk % mheap_.specialfinalizeralloc.size = 16 _FixAllocChunk % mheap_.specialprofilealloc.size = 16 _FixAllocChunk % mheap_.specialReachableAlloc.size = 16 _FixAllocChunk % mheap_.arenaHintAlloc.size = 16 After this commit, fixalloc alloc '_FixAllocChunk / fixalloc.size' objects exactly with zero waste. Sizeof(fixalloc{}) is unchanged. Change-Id: Ifc551f5b7aa9d842fa559abbe532ffcfb4d3540c GitHub-Last-Rev: e08b4c66b82bc7be9d14fb7eb7580504d777481e GitHub-Pull-Request: golang/go#47439 Reviewed-on: https://go-review.googlesource.com/c/go/+/338090 Reviewed-by: Austin Clements Run-TryBot: Austin Clements TryBot-Result: Go Bot Trust: Cherry Mui --- src/runtime/mfixalloc.go | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/runtime/mfixalloc.go b/src/runtime/mfixalloc.go index a81139a389c..b701a09b40a 100644 --- a/src/runtime/mfixalloc.go +++ b/src/runtime/mfixalloc.go @@ -30,7 +30,8 @@ type fixalloc struct { arg unsafe.Pointer list *mlink chunk uintptr // use uintptr instead of unsafe.Pointer to avoid write barriers - nchunk uint32 + nchunk uint32 // bytes remaining in current chunk + nalloc uint32 // size of new chunks in bytes inuse uintptr // in-use bytes now stat *sysMemStat zero bool // zero allocations @@ -63,6 +64,7 @@ func (f *fixalloc) init(size uintptr, first func(arg, p unsafe.Pointer), arg uns f.list = nil f.chunk = 0 f.nchunk = 0 + f.nalloc = uint32(_FixAllocChunk / size * size) // Round _FixAllocChunk down to an exact multiple of size to eliminate tail waste f.inuse = 0 f.stat = stat f.zero = true @@ -84,8 +86,8 @@ func (f *fixalloc) alloc() unsafe.Pointer { return v } if uintptr(f.nchunk) < f.size { - f.chunk = uintptr(persistentalloc(_FixAllocChunk, 0, f.stat)) - f.nchunk = _FixAllocChunk + f.chunk = uintptr(persistentalloc(uintptr(f.nalloc), 0, f.stat)) + f.nchunk = f.nalloc } v := unsafe.Pointer(f.chunk)