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runtime: make treap iteration more efficient

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This change introduces a treapIterFilter type which represents the
power set of states described by a treapIterType.

This change then adds a treapIterFilter field to each treap node
indicating the types of spans that live in that subtree. The field is
maintained via the same mechanism used to maintain maxPages. This allows
pred, succ, start, and end to be judicious about which subtrees it will
visit, ensuring that iteration avoids traversing irrelevant territory.

Without this change, repeated scavenging attempts can end up being N^2
as the scavenger walks over what it already scavenged before finding new
spans available for scavenging.

Finally, this change also only scavenges a span once it is removed from
the treap. There was always an invariant that spans owned by the treap
may not be mutated in-place, but with this change violating that
invariant can cause issues with scavenging.

For #30333.

Change-Id: I8040b997e21c94a8d3d9c8c6accfe23cebe0c3d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/174878
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Michael Anthony Knyszek 2019-05-01 18:02:14 +00:00 • committed by Michael Knyszek
parent 9baa4301cf
commit fa8470a8cd
4 changed files with 240 additions and 154 deletions
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12
src/runtime/export_test.go
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@ -546,15 +546,21 @@ func (s Span) Pages() uintptr {
return s.mspan.npages
}
type TreapIterType int
type TreapIterType treapIterType
const (
TreapIterScav TreapIterType = TreapIterType(treapIterScav)
TreapIterBits = treapIterBits
)
type TreapIterFilter treapIterFilter
func TreapFilter(mask, match TreapIterType) TreapIterFilter {
return TreapIterFilter(treapFilter(treapIterType(mask), treapIterType(match)))
}
func (s Span) MatchesIter(mask, match TreapIterType) bool {
return s.mspan.matchesIter(treapIterType(mask), treapIterType(match))
return treapFilter(treapIterType(mask), treapIterType(match)).matches(s.treapFilter())
}
type TreapIter struct {
@ -639,5 +645,5 @@ func (t *Treap) Size() int {
func (t *Treap) CheckInvariants() {
t.mTreap.treap.walkTreap(checkTreapNode)
t.mTreap.treap.validateMaxPages()
t.mTreap.treap.validateInvariants()
}