[8u] RFR backport of JDK-8198423: Improve metaspace chunk allocation

[Langer, Christoph]

Hi,

from a technical perspective, Thomas Stuefe is probably the right contact for this backport. And I see, he has already commented on it.

Whether it is appropriate for OpenJDK 8u and can make it there, you'll probably have to convince Andrew Haley and Andrew Hughes. I'm not a maintainer for 8u.

Best regards
Christoph

> -----Original Message-----
> From: Andrew Dinn <adinn at redhat.com>
> Sent: Dienstag, 24. September 2019 11:56
> To: Denghui Dong <denghui.ddh at alibaba-inc.com>; jdk8u-
> dev at openjdk.java.net; Andrew Haley <aph at redhat.com>; Langer,
> Christoph <christoph.langer at sap.com>
> Subject: Re: [8u] RFR backport of JDK-8198423: Improve metaspace chunk
> allocation
> 
> On 23/09/2019 10:49, Denghui Dong wrote:
> > Hi all,
> >   I'd like to request a backport of JDK-8198423.
> >   I found some long-time running application will oom caused by metaspace
> if
> > the application loads / unloads classes (by different classloaders)
> frequently,
> > even if there are many free chunks in freelist.
> > . . .
> >   This patch doesn't apply cleanly to 8u-dev, if you think this backport is
> reasonable,
> > i will provide my webrev.
> >   What's your comments?
> I think backporting this patch is probably a bad idea. It is a large and
> complex change to a critical part of the JVM runtime so the risk
> involved is quite high.
> 
> Likewise I would expect that backporting whatever eventually gets done
> under JDK-8221173 is going to be equally risky.
> 
> It might help if you could give an idea of how much of a problem this
> is. I can see how very long-running apps might suffer from fragmentation
> of metadata space without the patch. Is this something you are seeing
> regularly or intermittently?
> 
> I would expect that allocating more memory to the JVM can be used as a
> workaround to delay the onset/lower the frequency of this problem. Is
> there a reason why that approach is not available to you?
> 
> And, of course, there is always the option of upgrading to jdk11u.
> Eventually, that is going to be needed to resolve more and more of the
> problems remaining in jdk8u.
> 
> Perhaps Andrew Haley or Christoph Langer might be able to comment on
> this?
> 
> regards,
> 
> 
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
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