Add content for JEP 331 #312
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@JasonFengJ9 - please can you review this small update for JEP331. |
SueChaplain
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@pshipton - please can you merge? Jason is happy with the content and I resolved the merge conflict. |
| @@ -70,6 +71,16 @@ For compatibility, the [`-XX:OnOutOfMemoryError`](xxonoutofmemoryerror.md) OpenJ | |||
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| The VM now supports the allocation of huge pages on Linux when you use the `madvise` (`/sys/kernel/mm/transparent_hugepage/enabled`) setting. To enable this feature, set [`-XX:+TransparentHugePage`](xxtransparenthugepage.md) on the command line when you start your application. This option is currently not enabled by default. | |||
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| ###  Support for low-overhead heap profiling | |||
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Should there be an End of content tag?
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As it is on the title of the section I think it is ok. It is also consistent with other sections in that topic?
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It's not consistent with the ChaCha20 topic, which has the end mark.
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Erm ... so it is. And that's not consistent with other release topics either. OK - fixing to make the same in this topic.
docs/version0.15.md
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| <i class="fa fa-exclamation-triangle" aria-hidden="true"></i> **Restrictions:** JEP 331 is implemented for OpenJ9 with the following limitations: | ||
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| - The `balanced` and `metronome` garbage collection policies are not supported. | ||
| - The changes might not be compatible with the Health Center agent, which uses the same sampling interval. |
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"might not" seems strange. Can't we figure out whether they are incompatible or not?
@JasonFengJ9
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Depends. Health Center agent uses same sampling interval. If JEP331 JVMTI agent happens to have same interval values as the Health Center agent, there is no problem. Also if the Health Center agent just displays the sampling allocation without analysis associated with the interval value, there is no problem either.
However if the Health Center agent does rely on the sampling interval value initially passed via command line option, and JEP331 JVMTI agent changes it afterwards, the result will be wrong.
P.S. @charliegracie mentioned the sampling before JEP331 wasn't accurate, a fix is expected via eclipse-openj9/openj9#6024.
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I'm thinking we should clarify the release note with this information. "might not" makes it seem like we didn't know.
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Agreed. How about following:
JEP331 JVMTI agent uses same sampling interval as the Health Center agent. If both agents expect same interval value, there is no incompatibility, otherwise the Health Center agent will get incorrect results.
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So you are saying that if the JEP 331 agent and the health center agent are used at the same time, then Health Center won't work?
The JEP331 JVMTI agent and the Health Center agent both set a sampling interval, which by default is different. If both agents are used at the same time the Health Center agent will get incorrect results, unless the sampling intervals are adjusted to use the same value.
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Waiting for Jason to approve before merging.
OpenJ9 now provides an implementation of JEP 331, which enables heap profiling with minimal resources. There are a couple of restrictions, which are documented. Closes: eclipse-openj9#284 Signed-off-by: Sue Chaplain <[email protected]>
OpenJ9 now provides an implementation of JEP 331, which
enables heap profiling with minimal resources. There are
a couple of restrictions, which are documented.
Closes: #284
Signed-off-by: Sue Chaplain [email protected]