Integrated: 8240556: Abort concurrent mark after effective eager reclamation of humongous objects

[Thomas Schatzl]

On Tue, 15 Sep 2020 12:40:46 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this change that implements concurrent mark abort as proposed by Liang Mao from Alibaba.
> 
> Basically, if at the end of the concurrent start pause we notice that we went below the IHOP threshold (and it has been
> a concurrent start pause caused by humongous allocation), instead of scheduling a mark operation, we schedule a
> "concurrent undo" operation that undoes the changes.  Regarding the removal of the
> test/hotspot/jtreg/gc/stress/jfr/TestStressBigAllocationGCEventsWithG1.java test: it only ever accidentally worked in
> G1. G1 never sent the AllocationRequiringGC events for GCs caused by going over the IHOP threshold for humongous
> allocations that the test actually expects.  That test previously only worked because G1 could not reclaim the
> humongous objects fast enough so crossing the IHOP threshold causes a full concurrent mark. Allocations during that
> concurrent mark do not cause a GC that can reclaim these objects, so ultimately some young GC that sends the
> AllocationRequiringGC event will be sent.  With concurrent undo this is not guaranteed any more, i.e. only in
> environments where concurrent undo is slow (and we'll improve it soon) this test works.  The test is too timing
> dependent, and checking for the wrong thing in this case, so removing it.  Testing: tbd.

This pull request has now been integrated.

Changeset: 37b70282
Author:    Thomas Schatzl <tschatzl at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/37b70282
Stats:     380 lines in 15 files changed: 229 ins; 79 del; 72 mod

8240556: Abort concurrent mark after effective eager reclamation of humongous objects

Reviewed-by: sjohanss, ayang

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PR: https://git.openjdk.java.net/jdk/pull/177