RFR: 8169931: 8k class metaspace chunks misallocated from 4k chunk freelist

Thomas Stüfe thomas.stuefe at gmail.com
Wed Nov 23 07:42:12 UTC 2016

Hi Stefan,

this looks fine!


On Tue, Nov 22, 2016 at 10:37 PM, Stefan Karlsson <
stefan.karlsson at oracle.com> wrote:

> Hi all,
> Here are the update patch, with changes suggested by Coleen and Thomas:
>  http://cr.openjdk.java.net/~stefank/8169931/webrev.02.delta
>  http://cr.openjdk.java.net/~stefank/8169931/webrev.02
> Changes to the previous patch:
> * Removed list_chunk_size and instead used free_chunks(index)->size()
> * Removed the const qualifier from list_index, since free_chunks isn't
> declared const. Fixing this would have been a too large change for this bug
> fix.
> * Moved ChunkManager_test_list_index into the unit test section of
> metaspace.cpp
> * Fixed a broken assert
> Thanks,
> StefanK
> On 2016-11-22 15:54, Stefan Karlsson wrote:
>> Hi all,
>> Please, review this patch to fix a bug in ChunkManager::list_index():
>>  http://cr.openjdk.java.net/~stefank/8169931/webrev.01
>> There's a great description of the bug in the bug report:
>>  https://bugs.openjdk.java.net/browse/JDK-8169931
>> There are two conceptual parts of the metaspace. The _class_ metaspace,
>> and the _non-class_ metaspace. They have different chunk sizes, and while
>> querying for the list index of a humongous chunk in the class metaspace,
>> the code accidentally matched the size against the MediumChunk size of the
>> non-class metaspace.
>> I've changed the code to not query against the global ChunkSizes enum,
>> but rather the values stored inside the ChunkManager instances. Therefore,
>> the list_index() function was changed into an instance method.
>> I've written a unit test that provoked the bug. It's a simplified test
>> with vm asserts instead of gtest asserts. The reason is that the
>> ChunkManager class is currently located in metaspace.cpp, and is not
>> accessible from the gtest unit tests.
>> Testing: jprt, Kitchensink, parallel class loading tests
>> Thanks,
>> StefanK

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