RFR: 8049831: Metadata Full GCs are not triggered when CMSClassUnloadingEnabled is turned off
bengt.rutisson at oracle.com
Fri Jul 11 08:16:06 UTC 2014
On 2014-07-10 14:28, Stefan Karlsson wrote:
> Dmitry Fazunenko had a couple of offline comments.
> Latests version:
> On 2014-07-10 10:22, Stefan Karlsson wrote:
>> Hi all,
>> Please, review this fix to honor -XX:-CMSClassUnloadingEnabled
>> correctly in the metadata allocation failure path.
>> By default, CMS does class unloading after a concurrent marking
>> cycle. When the amount of metadata hits the high water mark
>> (capacity_until_GC), a concurrent cycle is initiated, the high water
>> mark is increased and the thread can proceed with the allocation. If
>> CMSClassUnloadingEnabled is turned off we don't unload classes after
>> a concurrent cycle, but instead relies on Full GCs to reclaim
>> metadata memory. The current code skips triggering a concurrent cycle
>> if CMSClassUnloadingEnabled is turned off, but it still allows the
>> high water mark to be increased and the thread can proceed with the
>> allocation without triggering a Full GC first. This defeats the
>> entire purpose of the high water mark.
>> The suggested fix is to not allow the increase of the high water mark
>> and the allocation if CMSClassUnloadingEnabled is turned off.
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