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runtime: eliminate write barriers from persistentalloc

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We're about to start tracking nowritebarrierrec through systemstack
calls, which will reveal write barriers in persistentalloc prohibited
by various callers.

The pointers manipulated by persistentalloc are always to off-heap
memory, so this removes these write barriers statically by introducing
a new go:notinheap type to represent generic off-heap memory.

Updates #22384.
For #22460.

Change-Id: Id449d9ebf145b14d55476a833e7f076b0d261d57
Reviewed-on: https://go-review.googlesource.com/72771
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2017-10-22 18:10:08 -04:00
parent 070cc8eb02
commit d941b07558
1 changed files with 23 additions and 7 deletions
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30
src/runtime/malloc.go
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@ -928,7 +928,7 @@ func nextSampleNoFP() int32 {
}
type persistentAlloc struct {
base unsafe.Pointer
base *notInHeap
off uintptr
}
@ -945,17 +945,17 @@ var globalAlloc struct {
//
// Consider marking persistentalloc'd types go:notinheap.
func persistentalloc(size, align uintptr, sysStat *uint64) unsafe.Pointer {
var p unsafe.Pointer
var p *notInHeap
systemstack(func() {
p = persistentalloc1(size, align, sysStat)
})
return p
return unsafe.Pointer(p)
}
// Must run on system stack because stack growth can (re)invoke it.
// See issue 9174.
//go:systemstack
func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
func persistentalloc1(size, align uintptr, sysStat *uint64) *notInHeap {
const (
chunk = 256 << 10
maxBlock = 64 << 10 // VM reservation granularity is 64K on windows
@ -976,7 +976,7 @@ func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
}
if size >= maxBlock {
return sysAlloc(size, sysStat)
return (*notInHeap)(sysAlloc(size, sysStat))
}
mp := acquirem()
@ -989,7 +989,7 @@ func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
}
persistent.off = round(persistent.off, align)
if persistent.off+size > chunk || persistent.base == nil {
persistent.base = sysAlloc(chunk, &memstats.other_sys)
persistent.base = (*notInHeap)(sysAlloc(chunk, &memstats.other_sys))
if persistent.base == nil {
if persistent == &globalAlloc.persistentAlloc {
unlock(&globalAlloc.mutex)
@ -998,7 +998,7 @@ func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
}
persistent.off = 0
}
p := add(persistent.base, persistent.off)
p := persistent.base.add(persistent.off)
persistent.off += size
releasem(mp)
if persistent == &globalAlloc.persistentAlloc {
@ -1011,3 +1011,19 @@ func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
}
return p
}
// notInHeap is off-heap memory allocated by a lower-level allocator
// like sysAlloc or persistentAlloc.
//
// In general, it's better to use real types marked as go:notinheap,
// but this serves as a generic type for situations where that isn't
// possible (like in the allocators).
//
// TODO: Use this as the return type of sysAlloc, persistentAlloc, etc?
//
//go:notinheap
type notInHeap struct{}
func (p *notInHeap) add(bytes uintptr) *notInHeap {
return (*notInHeap)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + bytes))
}