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runtime: break up large calls to memclrNoHeapPointers to allow preemption

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If something "huge" is allocated, and the zeroing is trivial (no pointers
involved) then zero it by chunks in a loop so that preemption can occur,
not all in a single non-preemptible call.

Benchmarking suggests that 256K is the best chunk size.

Updates #42642.

Change-Id: I94015e467eaa098c59870e479d6d83bc88efbfb4
Reviewed-on: https://go-review.googlesource.com/c/go/+/270943
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
David Chase 2020-11-17 19:54:31 -05:00
parent 41afd3af42
commit 0bbfc5c31e
4 changed files with 51 additions and 7 deletions
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7
src/runtime/mheap.go
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@ -897,7 +897,8 @@ func (s spanAllocType) manual() bool {
// spanclass indicates the span's size class and scannability.
//
// If needzero is true, the memory for the returned span will be zeroed.
func (h *mheap) alloc(npages uintptr, spanclass spanClass, needzero bool) *mspan {
// The boolean returned indicates whether the returned span is zeroed.
func (h *mheap) alloc(npages uintptr, spanclass spanClass, needzero bool) (*mspan, bool) {
// Don't do any operations that lock the heap on the G stack.
// It might trigger stack growth, and the stack growth code needs
// to be able to allocate heap.
@ -911,13 +912,15 @@ func (h *mheap) alloc(npages uintptr, spanclass spanClass, needzero bool) *mspan
s = h.allocSpan(npages, spanAllocHeap, spanclass)
})
isZeroed := s.needzero == 0
if s != nil {
if needzero && s.needzero != 0 {
memclrNoHeapPointers(unsafe.Pointer(s.base()), s.npages<<_PageShift)
isZeroed = true
}
s.needzero = 0
}
return s
return s, isZeroed
}
// allocManual allocates a manually-managed span of npage pages.