RFR: 8049831: Metadata Full GCs are not triggered when CMSClassUnloadingEnabled is turned off
stefan.karlsson at oracle.com
Thu Jul 10 09:38:41 UTC 2014
I decided to convert my adhoc test into a jtreg test that could be
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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