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runtime: record in-use spans in a page-indexed bitmap

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This adds a bitmap indexed by page number that marks the starts of
in-use spans. This will be used to quickly find in-use spans with no
marked objects for sweeping.

For #18155.

Change-Id: Icee56f029cde502447193e136fa54a74c74326dd
Reviewed-on: https://go-review.googlesource.com/c/138957
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Austin Clements 2018-09-26 16:32:52 -04:00
parent e500ffd88c
commit 69e666e4f7
1 changed files with 26 additions and 0 deletions
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26
src/runtime/mheap.go
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@ -193,6 +193,14 @@ type heapArena struct {
// must not be a safe-point between establishing that an
// address is live and looking it up in the spans array.
spans [pagesPerArena]*mspan
// pageInUse is a bitmap that indicates which spans are in
// state mSpanInUse. This bitmap is indexed by page number,
// but only the bit corresponding to the first page in each
// span is used.
//
// Writes are protected by mheap_.lock.
pageInUse [pagesPerArena / 8]uint8
}
// arenaHint is a hint for where to grow the heap arenas. See
@ -600,6 +608,16 @@ func spanOfHeap(p uintptr) *mspan {
return s
}
// pageIndexOf returns the arena, page index, and page mask for pointer p.
// The caller must ensure p is in the heap.
func pageIndexOf(p uintptr) (arena *heapArena, pageIdx uintptr, pageMask uint8) {
ai := arenaIndex(p)
arena = mheap_.arenas[ai.l1()][ai.l2()]
pageIdx = ((p / pageSize) / 8) % uintptr(len(arena.pageInUse))
pageMask = byte(1 << ((p / pageSize) % 8))
return
}
// Initialize the heap.
func (h *mheap) init() {
h.treapalloc.init(unsafe.Sizeof(treapNode{}), nil, nil, &memstats.other_sys)
@ -741,6 +759,10 @@ func (h *mheap) alloc_m(npage uintptr, spanclass spanClass, large bool) *mspan {
s.baseMask = m.baseMask
}
// Mark in-use span in arena page bitmap.
arena, pageIdx, pageMask := pageIndexOf(s.base())
arena.pageInUse[pageIdx] |= pageMask
// update stats, sweep lists
h.pagesInUse += uint64(npage)
if large {
@ -1039,6 +1061,10 @@ func (h *mheap) freeSpanLocked(s *mspan, acctinuse, acctidle bool, unusedsince i
throw("mheap.freeSpanLocked - invalid free")
}
h.pagesInUse -= uint64(s.npages)
// Clear in-use bit in arena page bitmap.
arena, pageIdx, pageMask := pageIndexOf(s.base())
arena.pageInUse[pageIdx] &^= pageMask
default:
throw("mheap.freeSpanLocked - invalid span state")
}