RFR (S) 8241139: Shenandoah: distribute mark-compact work exactly to minimize fragmentation
Roman Kennke
rkennke at redhat.com
Thu Mar 19 14:54:45 UTC 2020
Very nice! The changes look good to me.
Thanks,
Roman
> RFE:
> https://bugs.openjdk.java.net/browse/JDK-8241139
>
> Was following up on why JLinkTest fails with Shenandoah. Figured out the dynamic work distribution
> in mark-compact leaves alive regions in the middle of the heap. It is a generic problem with current
> mark-compact implementation, as which regions get into each worker slice is time-dependent.
>
> Consider the worst case scenario: two workers would have their slices interleaved, once slice is
> fully alive, and other is fully dead. In the end, mark-compact would finish with the same
> interleaved heap. A humongous allocation then fails. We need to plan the parallel sliding more
> accurately. See the code comments about what new plan does.
>
> Webrev:
> https://cr.openjdk.java.net/~shade/8241139/webrev.01/
>
> Testing: hotspot_gc_shenandoah; known-failing test; tier{1,2,3} (passed with previous version,
> running with new version now); eyeballing shenandoah-visualizer
>
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