[11u] RFR: 8258414: OldObjectSample events too expensive

[Jaroslav Bachorík]

Hi Florian,

a few nits:
- src/hotspot/share/jfr/leakprofiler/checkpoint/objectSampleCheckpoint.cpp
   L287 - IMO, the TODO is not necessary
   L293 - I think the comment `// caller needs ResourceMark` should
not be removed
   L303 - Not sure if using Module_lock instead of
ClassLoaderDataGraph_lock is correct. Also, this change seems to be
bringing in changes unrelated to the patch.
              From what is happening in other places it would seem
that a safepoint should be asserted instead (or nothing should be
done).
              I will let Markus weigh in on this.
- src/hotspot/share/jfr/support/jfrAllocationTracer.cpp
   L38 - can this be completely removed?
- src/hotspot/share/jfr/support/jfrAllocationTracer.hpp
  L30 - I think `class JfrThreadLocal;` can also be removed

Cheers,

-JB-


On Wed, Mar 24, 2021 at 8:42 PM Florian David
<florian.david at datadoghq.com> wrote:
>
> Hi,
>
> Please review this 11u backport. It's very similar to the original patch,
> except for the class loader data graph lock and JfrKlassUnloading::sort()
> method which are not available in 11u.
>
> The missing lock has been replaced by locking the module_lock instead,
> as it is done in jfrcheckpointManager.cpp:363.
> JfrKlassUnloading class does not exist and thus sort() method is not replaced,
> I added a TODO instead.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8258414
> webrev: http://cr.openjdk.java.net/~fdavid/8258414/webrev.00/
> Original PR: https://github.com/openjdk/jdk/pull/2780
>
> Testing:
> - Linux x86_64 tier1 tests
> - SPECvm 2008 on a 96 cores/192 Gib server. JFR recording size is 75.12 MB before the patch and 3.08 MB after the patch.
>
> Let me know what you think.
>
> Thanks,
> Florian