[crac] RFR: Wait until G1 GC has finished before creating a snapshot.

[Radim Vansa]

On Tue, 25 Jul 2023 11:24:38 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

> @rvansa did report his snapshots are about 2x-3x bigger than they should be. He then also found it only happens if the snapshot is done too quickly after GC should have been run.
> 
> One can reproduce the race case by:
> 
> --- a/src/hotspot/share/gc/g1/g1UncommitRegionTask.hpp
> +++ b/src/hotspot/share/gc/g1/g1UncommitRegionTask.hpp
> @@ -35,7 +35,7 @@ class G1UncommitRegionTask : public G1ServiceTask {
>    // is short, while still making reasonable progress.
>    static const uint UncommitSizeLimit = 128 * M;
>    // Initial delay in milliseconds after GC before the regions are uncommitted.
> -  static const uint UncommitInitialDelayMs = 100;
> +  static const uint UncommitInitialDelayMs = 10*1000;
>    // The delay between two uncommit task executions.
>    static const uint UncommitTaskDelayMs = 10;

@jankratochvil I confirm that this fixes the issue in `BigCheckpointTest` on my machine.

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PR Comment: https://git.openjdk.org/crac/pull/93#issuecomment-1649898077