f9497a6747
Currently sweeping walks the list of all spans, which means the work in sweeping is proportional to the maximum number of spans ever used. If the heap was once large but is now small, this causes an amortization failure: on a small heap, GCs happen frequently, but a full sweep still has to happen in each GC cycle, which means we spent a lot of time in sweeping. Fix this by creating a separate list consisting of just the in-use spans to be swept, so sweeping is proportional to the number of in-use spans (which is proportional to the live heap). Specifically, we create two lists: a list of unswept in-use spans and a list of swept in-use spans. At the start of the sweep cycle, the swept list becomes the unswept list and the new swept list is empty. Allocating a new in-use span adds it to the swept list. Sweeping moves spans from the unswept list to the swept list. This fixes the amortization problem because a shrinking heap moves spans off the unswept list without adding them to the swept list, reducing the time required by the next sweep cycle. Updates #9265. This fix eliminates almost all of the time spent in sweepone; however, markrootSpans has essentially the same bug, so now the test program from this issue spends all of its time in markrootSpans. No significant effect on other benchmarks. Change-Id: Ib382e82790aad907da1c127e62b3ab45d7a4ac1e Reviewed-on: https://go-review.googlesource.com/30535 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> |
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