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List: openjdk-hotspot-runtime-dev
Subject: Re: RFR(S) 8176887: SIGSEGV in AOTCodeHeap::next when using specific configuration
From: Igor Veresov <igor.veresov () oracle ! com>
Date: 2017-04-10 21:13:11
Message-ID: 1A4DC886-8121-4D43-B756-C45AEDA7BACC () oracle ! com
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Thanks, Coleen!
igor
> On Apr 10, 2017, at 1:22 PM, coleen.phillimore@oracle.com wrote:
>
>
>
> On 4/10/17 3:48 PM, Igor Veresov wrote:
> > So… I'm ok to assume that you're ok with this fix for the time being?
>
> If these MethodCounters aren't added to the CDS archive, then the vptr only adds \
> space and I think it's ok for now. Coleen
>
> >
> > igor
> >
> > > On Apr 7, 2017, at 3:43 PM, Igor Veresov <igor.veresov@oracle.com \
> > > <mailto:igor.veresov@oracle.com>> wrote:
> > > >
> > > > On Apr 7, 2017, at 2:36 PM, coleen.phillimore@oracle.com \
> > > > <mailto:coleen.phillimore@oracle.com> wrote:
> > > >
> > > >
> > > > On 4/7/17 5:33 PM, Igor Veresov wrote:
> > > > > > On Apr 7, 2017, at 1:29 PM, Vladimir Kozlov <vladimir.kozlov@oracle.com \
> > > > > > <mailto:vladimir.kozlov@oracle.com>> wrote:
> > > > > > This could be good fix for JDK 9.
> > > > > >
> > > > > > Are you sure that functions called for Metadata scan will not barf on \
> > > > > > MethodCounters?
> > > > > Yes, there shouldn't be any problems. In the context of class redefinition \
> > > > > it calls mark_on_stack(), which is empty by default except for Method and \
> > > > > ConstantPool.
> > > > > > You need also ask Runtime group to look on this change.
> > > > > CCing the runtime mail list. Guys, any objections to making MethodCounters \
> > > > > a Metadata ?
> > > >
> > > > If you make MethodCounters inherited by Metadata it will have a vptr. It \
> > > > doesn't otherwise.
> > >
> > > Yes, but I'd have to have some type id to filter them out anyway (if they are \
> > > in an array with other metaspace objects), having a vtbl seems like an \
> > > equivalent solution.
> > > > >
> > > > > > When fixing 8173794 I missed this case (MethodCounters*). We should not \
> > > > > > put them into metaspace_got array since GC don't need to process them. \
> > > > > > And they increase metaspace_got array significantly.
> > > > > > For 10 we should fix JAPTC code - metaspace_got array should contain only \
> > > > > > Klass* pointers. May be to add a separate array since \
> > > > > > extLinkageGOTContainer may not right for MethodCounters*.
> > > > >
> > > > > In the context of class redefinition the scan is actually interested only \
> > > > > in methods, rather than classes. Going forward, yes, it would probably be \
> > > > > better if we had separate GOT arrays for each MetaspaceObj subtype, so that \
> > > > > we can separate Methods out and scan only them.
> > > >
> > > > Can you have a special array for Method*s?
> > >
> > > Yes, that's what would be best to do in the future. But it is a substantially \
> > > bigger change, I'm not sure it would be appropriate for 9 at this point.
> > > igor
> > >
> > > > Coleen
> > > >
> > > > > igor
> > > > >
> > > > > > Thanks,
> > > > > > Vladimir
> > > > > >
> > > > > > On 4/7/17 11:55 AM, Igor Veresov wrote:
> > > > > > > The problem here is that AOTCodeHeap::got_metadata_do() iterates over \
> > > > > > > the _metaspace_got array assuming that the array contains Metadata*, \
> > > > > > > indeed the array is declared as such. However it also happens to \
> > > > > > > contain MethodCounters*, and MethodCounters is not Metadata, but \
> > > > > > > MetaspaceObj. The simplest and minimal risk solution is to make \
> > > > > > > MethodCounters a subclass of Metadata (we'd like to have this fix in \
> > > > > > > jdk9).
> > > > > > >
> > > > > > > Webrev: http://cr.openjdk.java.net/~iveresov/8176887/webrev.00/ \
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> > > > > > > JBS: https://bugs.openjdk.java.net/browse/JDK-8176887 \
> > > > > > > <https://bugs.openjdk.java.net/browse/JDK-8176887>
> > > > > > > Thanks!
> > > > > > > igor
> >
>
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