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

[Ioi Lam]

Hi Calvin, thanks for the review.


On 11/2/18 12:30 PM, Calvin Cheung wrote:
> Hi Ioi,
>
> The revised webrev looks good.
>
> The following is removed from systemDictionaryShared.cpp:
> 831     log_info(cds, verification)("Recorded verification constraints 
> for %d classes = %d bytes (avg = %.2f bytes) ", count, bytes, avg);
>
> Please make sure no test is expecting the above output.
I checked all CDS tests and there's no tests for that expects the above 
output.
>
> Line 790 in the same file is a bit too long, consider break it into 2 
> lines.
>
Done. I also broke the same line in 
SystemDictionaryShared::add_verification_constraint into two lines.

Thanks
- Ioi
> thanks,
> Calvin
>
>
> On 11/1/18, 9:47 PM, Ioi Lam wrote:
>> Hi,
>>
>> 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!
>>
>> http://cr.openjdk.java.net/~iklam/jdk12/8213250-cds-dump-run-out-of-metaspace.v02/ 
>>
>>
>> The original bug that caused the "!(DumpSharedSpaces && 
>> THREAD->is_VM_thread())" check to be added in Metaspace::allocate() was
>>
>>     https://bugs.openjdk.java.net/browse/JDK-8196626
>>     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.
>>
>> Thanks
>> - 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
>>