Fragmentation and UseCMSInitiatingOccupancyOnly

[Gustav Åkesson]

Hi,

In case UseCMSInitiatingOccupancyOnly is enabled we instruct CMS to start
at X% of old gen, and not try to figure out by itself when to start. My
understanding is that when flag is disabled, CMS is aiming for X%, but uses
statistics of previous collections (GC rate, GC time) to determine when to
initiate.

My question is whether enabling UseCMSInitiatingOccupancyOnly increases the
risk of promotion failure (FullGC) due to fragmentation, meaning that it
will always honor X% rule and rather generate promotion failure event than
run CMS prematurely?

Or, in case flag is disabled, is CMS smart enough to start prior to X% when
heap is fragmented instead of generating promotion failure?


Best Regards,

Gustav Åkesson
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/hotspot-gc-use/attachments/20140122/92e95a10/attachment.html