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runtime: add packed bitmap summaries

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This change adds the concept of summaries and of summarizing a set of
pallocBits, a core concept in the new page allocator. These summaries
are really just three integers packed into a uint64. This change also
adds tests and a benchmark for generating these summaries.

Updates #35112.

Change-Id: I69686316086c820c792b7a54235859c2105e5fee
Reviewed-on: https://go-review.googlesource.com/c/go/+/190621
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Michael Anthony Knyszek 2019-09-25 15:55:29 +00:00 • committed by Michael Knyszek
parent b3a361337c
commit cec01395c5
4 changed files with 293 additions and 0 deletions
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35
src/runtime/export_test.go
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@ -735,6 +735,14 @@ const (
PallocChunkPages = pallocChunkPages
)
// Expose pallocSum for testing.
type PallocSum pallocSum
func PackPallocSum(start, max, end uint) PallocSum { return PallocSum(packPallocSum(start, max, end)) }
func (m PallocSum) Start() uint { return pallocSum(m).start() }
func (m PallocSum) Max() uint { return pallocSum(m).max() }
func (m PallocSum) End() uint { return pallocSum(m).end() }
// Expose pallocBits for testing.
type PallocBits pallocBits
@ -743,6 +751,33 @@ func (b *PallocBits) Find(npages uintptr, searchIdx uint) (uint, uint) {
}
func (b *PallocBits) AllocRange(i, n uint) { (*pallocBits)(b).allocRange(i, n) }
func (b *PallocBits) Free(i, n uint) { (*pallocBits)(b).free(i, n) }
func (b *PallocBits) Summarize() PallocSum { return PallocSum((*pallocBits)(b).summarize()) }
// SummarizeSlow is a slow but more obviously correct implementation
// of (*pallocBits).summarize. Used for testing.
func SummarizeSlow(b *PallocBits) PallocSum {
var start, max, end uint
const N = uint(len(b)) * 64
for start < N && (*pageBits)(b).get(start) == 0 {
start++
}
for end < N && (*pageBits)(b).get(N-end-1) == 0 {
end++
}
run := uint(0)
for i := uint(0); i < N; i++ {
if (*pageBits)(b).get(i) == 0 {
run++
} else {
run = 0
}
if run > max {
max = run
}
}
return PackPallocSum(start, max, end)
}
// Expose non-trivial helpers for testing.
func FindBitRange64(c uint64, n uint) uint { return findBitRange64(c, n) }