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

[Thomas Stüfe]

I agree with Andrew that backporting JDK-8198423 is a large effort and a
bit risky. If that has not been clear from my first mail I recommend
against it.

As for JDK-8221173, lets see how that pans out. I plan to bring it at least
to SapMachine11, upstream 11 if it makes sense. But this is still in the
future.

Cheers, Thomas


On Tue, Sep 24, 2019 at 2:22 PM Langer, Christoph <christoph.langer at sap.com>
wrote:

> 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
> > Red Hat UK Ltd
> > Registered in England and Wales under Company Registration No. 03798903
> > Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander
>