concurrent mode failure during concurrent sweep phase

[Kirk Pepperdine]

Hi Jon,

Thanks for the response, I don't believe the sweep has completed as that phase is pre-empted by the concurrent mode failure. If the promotion fails outside of a CMS phase then it seems to go directly to a Full GC without registering a CMF.

I guess one of the assumptions that I was under was that any newly freed space wouldn't be visible until after the CMS-reset.

Regards,
Kirk

On 2012-08-15, at 4:46 PM, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:

> Kirk,
> 
> In this case the sweep has completed, right?  So no additional free space is
> going to be found.   Even if we delayed the young gen collection, it would still
> fail.
> 
> In general there is a way to get CMS to hold off the young gen collection
> by completing the concurrent collection in a STW phase.   I can't swear
> that it still works but the idea was that if we were sweeping (I think), we should
> move the collection from a concurrent collection to a STW collection
> and finish the sweep during a STW.  I've only seen it worsen the
> situation (i.e., the sweeping is so slow that it is much faster to do the
> full collection).  I think that code should be ripped out.
> 
> Jon
> 
> 
> On 8/15/2012 5:01 AM, Kirk Pepperdine wrote:
>> Hi all,
>> 
>> : 81092K->81092K(81856K), 0.3419045 secs]5274.145: [CMS5281.056: [CMS-concurrent-sweep: 11.066/12.602 secs]
>> 
>> In all of the GC logs I've got, this one doesn't show up very often. Now that I'm looking at it I'm asking myself... does it really make sense to declare a CMF when one is so close to the end of the CMS cycle? This really literally just small numbers of instructions away from the CMS-reset.... Wouldn't it make more sense to delay the ParNew that is hoisting survivors into CMS tenured vs triggering a full gc with it's (most likely longer) STW pause? Or is this a signal that the failure is most likely due to high fragmentation?
>> 
>> Regards,
>> Kirk