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runtime: check transition condition before triggering periodic GC

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Currently sysmon triggers periodic GC if GC is not currently running
and it's been long enough since the last GC. This misses some
important conditions; for example, whether GC is enabled at all by
GOGC. As a result, if GOGC is off, once we pass the timeout for
periodic GC, sysmon will attempt to trigger a GC every 10ms. This GC
will be a no-op because gcStart will check all of the appropriate
conditions and do nothing, but it still goes through the motions of
waking the forcegc goroutine and printing a gctrace line.

Fix this by making sysmon call gcShouldStart to check *all* of the
appropriate transition conditions before attempting to trigger a
periodic GC.

Fixes #19247.

Change-Id: Icee5521ce175e8419f934723849853d53773af31
Reviewed-on: https://go-review.googlesource.com/37515
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 2017-02-23 11:04:37 -05:00
parent 1be3e76e76
commit 640cd3b322
1 changed files with 1 additions and 1 deletions
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2
src/runtime/proc.go
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@ -3791,7 +3791,7 @@ func sysmon() {
}
// check if we need to force a GC
lastgc := int64(atomic.Load64(&memstats.last_gc_nanotime))
if gcphase == _GCoff && lastgc != 0 && now-lastgc > forcegcperiod && atomic.Load(&forcegc.idle) != 0 {
if gcShouldStart(true) && lastgc != 0 && now-lastgc > forcegcperiod && atomic.Load(&forcegc.idle) != 0 {
lock(&forcegc.lock)
forcegc.idle = 0
forcegc.g.schedlink = 0