CMS does not want to run concurrently

Y Srinivas Ramakrishna Y.S.Ramakrishna at Sun.COM
Wed Dec 17 12:12:20 PST 2008


Just a quick remark related to:-

...
> Here in the CMS gen (old generation) it is only 325384K full (out of
> a total of 659140K) when the collection starts.  Actually, you might
> have a severely fragmented heap.  In that case Full GC's would happen
> and using the survivor spaces would help.

When you have a fragmented heap that causes a full collection
the gc log message (in 5u8) would look a bit different as a
scavenge is first attempted, but fails because of a fragmented
heap, and then bails to a full collection. Because I do not see
that abortive scavenge attempt logged here, I suspect this may not
be a fragmentation-induced full gc, but perhaps something
else. Nonetheless, Jon's suggestion of using survivor spaces
to stem the tenuring of very young objects would be a good
thing to reduce fragmentation and other stresses on CMS.

-- ramki
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