RFC: Piggy-back monitor-deflation and nmethod-marking on GC

Roman Kennke rkennke at redhat.com
Fri Sep 14 14:56:17 UTC 2018

> Regarding those issues:
> https://bugs.openjdk.java.net/browse/JDK-8132849
> https://bugs.openjdk.java.net/browse/JDK-8132849

Oops. I meant to include:


> I.e. increased pause times caused by monitor-deflation and
> nmethod-marking, there has been the suggestion by the reporter to
> piggy-back those activities on GC thread-scanning.
> We do have code in Shenandoah that does this since quite a while.
> The idea is to introduce two new methods in VM_Operation:
>   virtual bool deflates_idle_monitors();
>   virtual bool marks_nmethods();
> That basically tell the runtime whether or not a particular VM_Operation
> (e.g. InitMark) can take over any of the two activties, and if so, skip
> the corresponding activity in the preceding SP-cleanup phase. This means
> that the VM_Operation needs to handle this itself. The change also
> includes some changes in sychronizer, thread etc to make this relatively
> easy to implement from a GC standpoint.
> Question: would there be interest in getting this upstreamed? If so, I
> would put together a patch for reviewing.
> Alternatively or additionally, at least for monitor deflation, there is
> the JEP Draft: Concurrent Monitor Deflation:
> https://bugs.openjdk.java.net/browse/JDK-8183909
> But this seems like a very serious amount of work.
> Roman

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