RFR(XS) 8213250 CDS archive creation aborts due to metaspace object allocation failure

Ioi Lam ioi.lam at oracle.com
Fri Nov 2 04:47:30 UTC 2018


I've revised the webrev to get to the the root of the problem -- we 
shouldn't allocate metaspace objects from within the VM Thread!


The original bug that caused the "!(DumpSharedSpaces && 
THREAD->is_VM_thread())" check to be added in Metaspace::allocate() was

     UseAppCDS.java crashes with "VM thread using lock Heap_lock (not 
allowed to block on)"

The fix in JDK-8196626 is just a band-aid solution -- avoiding the GC. 
The proper fix is not to do any allocation inside the VM thread. So 
instead of calling finalize_verification_constraints, which allocates 
MetaspaceObjs, very late in the CDS dumping process, now we call be as 
soon as a class has been verified.

- Ioi

On 11/1/18 11:07 AM, Ioi Lam wrote:
> https://bugs.openjdk.java.net/browse/JDK-8213250
> http://cr.openjdk.java.net/~iklam/jdk12/8213250-cds-dump-run-out-of-metaspace.v01/ 
> When Metaspace::allocate() fails, usually we first try to GC to see if
> some MetaspaceObjs can be freed. This is an optimization to avoid 
> prematurely
> expanding the metaspace.
> However, GC cannot run in the last phase of CDS which runs inside the 
> VM thread.
> The old code just aborts the CDS dump. The fix is to unconditionally 
> expand the
> metaspace without doing a GC.
> (During GC dump time, no classes are unloaded, so even if we force a 
> GC, it would
> not free up any metaspace anyway).
> Testing:
> Before the fix, the test case (jruby) would fail to dump once a couple 
> of times. Now
> it has dumped hundreds of times without failure.
> I am also running hs-tier 1/2
> Thanks
> - Ioi

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