RFR(xxs): 8202424: Metaspace: on chunk retirement, use correct lower limit on chunksize when adding blocks to free blocks list.

[Thomas Stüfe]

Thanks Zhengyu!

On Thu, May 3, 2018 at 3:24 PM, Zhengyu Gu <zgu at redhat.com> wrote:
> Looks good to me.
>
> -Zhengyu
>
>
> On 05/03/2018 09:02 AM, Thomas Stüfe wrote:
>>
>> Hi all,
>>
>> jdk-submit tests all went thru on this one.
>>
>> I still need reviewers.
>>
>> Thanks, Thomas
>>
>>
>> On Mon, Apr 30, 2018 at 4:07 PM, Thomas Stüfe <thomas.stuefe at gmail.com>
>> wrote:
>>>
>>> Hi all,
>>>
>>> please review this small fix, which fixes a small metaspace leak when
>>> retiring chunks.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8202424
>>> Webrev:
>>> http://cr.openjdk.java.net/~stuefe/webrevs/8202424-Metaspace-on-chunk-retirement-use-correct-lower-limit-on-chunksize-when-adding-blocks-to-free-blocks-list/webrev.00/webrev/
>>>
>>> Some time ago, JDK-8164921 got rid of dark matter by lowering the
>>> smallest block size which can be managed by the free block list to
>>> sizeof(MetaBlock).
>>>
>>> When retiring chunks, the leftover space in the old chunk is added to
>>> the free block list via SpaceManager::deallocate(). Here, we still
>>> unnecessarily assume a lower size limit of TreeChunk<Metablock,
>>> FreeList<Metablock> >::min_size(), which is unnecessary high and
>>> causes leaks which show up as waste in the retired chunks.
>>>
>>> By correctly using SmallBlocks::small_block_min_size() when
>>> deallocating the leftover chunk space on chunk retirement, we can
>>> reduce that kind of waste to almost nil.
>>>
>>> Thanks, Thomas