Request for review (S): 7166894 Add gc cause to Full GC logging for all collectors

Bengt Rutisson bengt.rutisson at oracle.com
Fri May 11 11:30:16 UTC 2012


Hi Kris,

Thanks again for looking at this.

I had to make some minor changes make it compile on all platforms. 
Mostly some explicit casts to const char*. Here is an updated webrev:
http://cr.openjdk.java.net/~brutisso/7166894/webrev.04/

More comments inline.

On 2012-05-08 16:43, Krystal Mok wrote:
> Hi Bengt,
>
> The current factoring looks nice and uniform. Thanks :-)
>
> But for most minor GCs and both CMS pause phases, the extra logging 
> doesn't really give additional information.
> Most minor GCs are going to say "Allocation Failure", and the two CMS 
> phases would change from, e.g.
>
> [GC [1 CMS-initial-mark
>
> to something like
>
> [GC (CMS Initial Mark) [1 CMS-initial-mark
>
> which is probably reasonable given the scope of the change, but not 
> really helpful.
> The "real cause", such as which generation (or perhaps System.gc() 
> with ExplicitGCInvokesConcurrent, or even GC locker) is triggering 
> this collection cycle, may be more useful, but it's hard to fit into 
> the current form.

Yes, I think you are correct in both cases. The gc cause that we have 
available does not always add a lot of information. This is relevant to 
fix but it is a slightly different issue than what this patch sets out 
to fix. Let's try to get this in first and then evaluate how the GC 
causes should be set.

Thanks,
Bengt

>
> - Kris
>
> On Tue, May 8, 2012 at 10:18 PM, Bengt Rutisson 
> <bengt.rutisson at oracle.com <mailto:bengt.rutisson at oracle.com>> wrote:
>
>
>     Hi again everyone,
>
>     It seems like the feedback on hotspot-gc-use is that we should add
>     the GC cause to all collectors but also provide a switch to turn
>     this logging off.
>
>     Here is an updated webrev:
>     http://cr.openjdk.java.net/~brutisso/7166894/webrev.03/
>     <http://cr.openjdk.java.net/%7Ebrutisso/7166894/webrev.03/>
>
>     Changes:
>     * GC cause logged for all collectors
>     * Added the flag -XX:-PrintGCCause to turn the new information off
>     * Refactored the string concatenation code into a helper class
>
>     I guess I will also have to update the CR to now reflect the fact
>     that this does not just concern full GCs anymore.
>
>     Thanks,
>     Bengt
>

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