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runtime: make runtime.GC, debug.FreeOSMemory concurrent #18216

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rsc opened this issue Dec 6, 2016 · 6 comments

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commented Dec 6, 2016

We've seen servers get utterly wedged because code incorrectly calls runtime.GC or debug.FreeOSMemory. Especially if multiple goroutines all decide this is necessary at the same time and stack up.

The implementations should both (1) use a concurrent GC, blocking of course until the GC is done, and (2) unblock all calls that arrived _before the GC started, so that if you call runtime.GC from 100 goroutines all at once, then you get something like two GCs (whatever starts first, and then the other 99 or so show up during the first GC, which kicks off one more).

@rsc rsc added this to the Go1.9Early milestone Dec 6, 2016

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commented Feb 27, 2017

CL https://golang.org/cl/37516 mentions this issue.

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commented Feb 27, 2017

CL https://golang.org/cl/37518 mentions this issue.

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commented Feb 27, 2017

CL https://golang.org/cl/37520 mentions this issue.

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commented Feb 27, 2017

CL https://golang.org/cl/37519 mentions this issue.

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commented Mar 2, 2017

CL https://golang.org/cl/37716 mentions this issue.

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commented Mar 30, 2017

CL https://golang.org/cl/38951 mentions this issue.

gopherbot pushed a commit that referenced this issue Mar 31, 2017

runtime: generalize GC trigger
Currently the GC triggering condition is an awkward combination of the
gcMode (whether or not it's gcBackgroundMode) and a boolean
"forceTrigger" flag.

Replace this with a new gcTrigger type that represents the range of
transition predicates we need. This has several advantages:

1. We can remove the awkward logic that affects the trigger behavior
   based on the gcMode. Now gcMode purely controls whether to run a
   STW GC or not and the gcTrigger controls whether this is a forced
   GC that cannot be consolidated with other GC cycles.

2. We can lift the time-based triggering logic in sysmon to just
   another type of GC trigger and move the logic to the trigger test.

3. This sets us up to have a cycle count-based trigger, which we'll
   use to make runtime.GC trigger concurrent GC with the desired
   consolidation properties.

For #18216.

Change-Id: If9cd49349579a548800f5022ae47b8128004bbfc
Reviewed-on: https://go-review.googlesource.com/37516
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

gopherbot pushed a commit that referenced this issue Mar 31, 2017

runtime: make debug.FreeOSMemory call runtime.GC()
Currently freeOSMemory calls gcStart directly, but we really just want
it to behave like runtime.GC() and then perform a scavenge, so make it
call runtime.GC() rather than gcStart.

For #18216.

Change-Id: I548ec007afc788e87d383532a443a10d92105937
Reviewed-on: https://go-review.googlesource.com/37518
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

gopherbot pushed a commit that referenced this issue Mar 31, 2017

runtime: track forced GCs independent of gcMode
Currently gcMode != gcBackgroundMode implies this was a user-forced GC
cycle. This is no longer going to be true when we make runtime.GC()
trigger a concurrent GC, so replace this with an explicit
work.userForced bit.

For #18216.

Change-Id: If7d71bbca78b5f0b35641b070f9d457f5c9a52bd
Reviewed-on: https://go-review.googlesource.com/37519
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

gopherbot pushed a commit that referenced this issue Mar 31, 2017

runtime: don't adjust GC trigger on forced GC
Forced GCs don't provide good information about how to adjust the GC
trigger. Currently we avoid adjusting the trigger on forced GC because
forced GC is also STW and we don't adjust the trigger on STW GC.
However, this will become a problem when forced GC is concurrent.

Fix this by skipping trigger adjustment if the GC was user-forced.

For #18216.

Change-Id: I03dfdad12ecd3cfeca4573140a0768abb29aac5e
Reviewed-on: https://go-review.googlesource.com/38951
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

gopherbot pushed a commit that referenced this issue Mar 31, 2017

runtime: track the number of active sweepone calls
sweepone returns ^uintptr(0) when there are no more spans to *start*
sweeping, but there may be spans being swept concurrently at the time
and there's currently no efficient way to tell when the sweeper is
done sweeping all the spans.

We'll need this for concurrent runtime.GC(), so add a count of the
number of active sweepone calls to make it possible to block until
sweeping is truly done.

This is also useful for more accurately printing the gcpacertrace,
since that should be printed after all of the sweeping stats are in
(currently we can print it slightly too early).

For #18216.

Change-Id: I06e6240c9e7b40aca6fd7b788bb6962107c10a0f
Reviewed-on: https://go-review.googlesource.com/37716
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

@gopherbot gopherbot closed this in 9ffbdab Mar 31, 2017

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: generalize GC trigger
Currently the GC triggering condition is an awkward combination of the
gcMode (whether or not it's gcBackgroundMode) and a boolean
"forceTrigger" flag.

Replace this with a new gcTrigger type that represents the range of
transition predicates we need. This has several advantages:

1. We can remove the awkward logic that affects the trigger behavior
   based on the gcMode. Now gcMode purely controls whether to run a
   STW GC or not and the gcTrigger controls whether this is a forced
   GC that cannot be consolidated with other GC cycles.

2. We can lift the time-based triggering logic in sysmon to just
   another type of GC trigger and move the logic to the trigger test.

3. This sets us up to have a cycle count-based trigger, which we'll
   use to make runtime.GC trigger concurrent GC with the desired
   consolidation properties.

For golang#18216.

Change-Id: If9cd49349579a548800f5022ae47b8128004bbfc
Reviewed-on: https://go-review.googlesource.com/37516
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: make debug.FreeOSMemory call runtime.GC()
Currently freeOSMemory calls gcStart directly, but we really just want
it to behave like runtime.GC() and then perform a scavenge, so make it
call runtime.GC() rather than gcStart.

For golang#18216.

Change-Id: I548ec007afc788e87d383532a443a10d92105937
Reviewed-on: https://go-review.googlesource.com/37518
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: track forced GCs independent of gcMode
Currently gcMode != gcBackgroundMode implies this was a user-forced GC
cycle. This is no longer going to be true when we make runtime.GC()
trigger a concurrent GC, so replace this with an explicit
work.userForced bit.

For golang#18216.

Change-Id: If7d71bbca78b5f0b35641b070f9d457f5c9a52bd
Reviewed-on: https://go-review.googlesource.com/37519
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: don't adjust GC trigger on forced GC
Forced GCs don't provide good information about how to adjust the GC
trigger. Currently we avoid adjusting the trigger on forced GC because
forced GC is also STW and we don't adjust the trigger on STW GC.
However, this will become a problem when forced GC is concurrent.

Fix this by skipping trigger adjustment if the GC was user-forced.

For golang#18216.

Change-Id: I03dfdad12ecd3cfeca4573140a0768abb29aac5e
Reviewed-on: https://go-review.googlesource.com/38951
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: track the number of active sweepone calls
sweepone returns ^uintptr(0) when there are no more spans to *start*
sweeping, but there may be spans being swept concurrently at the time
and there's currently no efficient way to tell when the sweeper is
done sweeping all the spans.

We'll need this for concurrent runtime.GC(), so add a count of the
number of active sweepone calls to make it possible to block until
sweeping is truly done.

This is also useful for more accurately printing the gcpacertrace,
since that should be printed after all of the sweeping stats are in
(currently we can print it slightly too early).

For golang#18216.

Change-Id: I06e6240c9e7b40aca6fd7b788bb6962107c10a0f
Reviewed-on: https://go-review.googlesource.com/37716
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

lparth added a commit to lparth/go that referenced this issue Apr 13, 2017

runtime: make runtime.GC() trigger a concurrent GC
Currently runtime.GC() triggers a STW GC. For common uses in tests and
benchmarks, it doesn't matter whether it's STW or concurrent, but for
uses in servers for things like collecting heap profiles and
controlling memory footprint, this pause can be a bit problem for
latency.

This changes runtime.GC() to trigger a concurrent GC. In order to
remain as close as possible to its current meaning, we define it to
always perform a full mark/sweep GC cycle before returning (even if
that means it has to finish up a cycle we're in the middle of first)
and to publish the heap profile as of the triggered mark termination.
While it must perform a full cycle, simultaneous runtime.GC() calls
can be consolidated into a single full cycle.

Fixes golang#18216.

Change-Id: I9088cc5deef4ab6bcf0245ed1982a852a01c44b5
Reviewed-on: https://go-review.googlesource.com/37520
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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