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[dev.garbage] runtime: refactor next free object
In preparation for changing how the next free object is chosen refactor and consolidate code into a single function. Change-Id: I6836cd88ed7cbf0b2df87abd7c1c3b9fabc1cbd8 Reviewed-on: https://go-review.googlesource.com/19317 Reviewed-by: Austin Clements <austin@google.com>
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@ -496,6 +496,32 @@ const (
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_FlagNoZero = 1 << 1 // don't zero memory
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)
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// nextFree returns the next free object from the cached span if one is available.
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// Otherwise it refills the cache with a span with an available object and
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// returns that object along with a flag indicating that this was a heavy
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// weight allocation. If it is a heavy weight allocation the caller must
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// determine whether a new GC cycle needs to be started or if the GC is active
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// whether this goroutine needs to assist the GC.
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// https://golang.org/cl/5350 motivates why this routine should preform a
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// prefetch.
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func (c *mcache) nextFree(sizeclass int8) (v gclinkptr, shouldhelpgc bool) {
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s := c.alloc[sizeclass]
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v = s.freelist
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if v.ptr() == nil {
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systemstack(func() {
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c.refill(int32(sizeclass))
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})
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shouldhelpgc = true
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s = c.alloc[sizeclass]
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v = s.freelist
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}
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s.freelist = v.ptr().next
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s.ref++
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// prefetchnta offers best performance, see change list message.
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prefetchnta(uintptr(v.ptr().next))
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return
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}
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// Allocate an object of size bytes.
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// Small objects are allocated from the per-P cache's free lists.
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// Large objects (> 32 kB) are allocated straight from the heap.
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@ -554,7 +580,6 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
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shouldhelpgc := false
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dataSize := size
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c := gomcache()
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var s *mspan
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var x unsafe.Pointer
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if size <= maxSmallSize {
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if flags&flagNoScan != 0 && size < maxTinySize {
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@ -606,20 +631,8 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
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return x
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}
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// Allocate a new maxTinySize block.
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s = c.alloc[tinySizeClass]
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v := s.freelist
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if v.ptr() == nil {
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systemstack(func() {
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c.refill(tinySizeClass)
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})
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shouldhelpgc = true
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s = c.alloc[tinySizeClass]
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v = s.freelist
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}
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s.freelist = v.ptr().next
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s.ref++
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// prefetchnta offers best performance, see change list message.
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prefetchnta(uintptr(v.ptr().next))
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var v gclinkptr
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v, shouldhelpgc = c.nextFree(tinySizeClass)
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x = unsafe.Pointer(v)
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(*[2]uint64)(x)[0] = 0
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(*[2]uint64)(x)[1] = 0
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@ -638,20 +651,8 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
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sizeclass = size_to_class128[(size-1024+127)>>7]
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}
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size = uintptr(class_to_size[sizeclass])
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s = c.alloc[sizeclass]
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v := s.freelist
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if v.ptr() == nil {
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systemstack(func() {
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c.refill(int32(sizeclass))
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})
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shouldhelpgc = true
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s = c.alloc[sizeclass]
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v = s.freelist
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}
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s.freelist = v.ptr().next
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s.ref++
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// prefetchnta offers best performance, see change list message.
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prefetchnta(uintptr(v.ptr().next))
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var v gclinkptr
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v, shouldhelpgc = c.nextFree(sizeclass)
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x = unsafe.Pointer(v)
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if flags&flagNoZero == 0 {
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v.ptr().next = 0
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