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

Bengt Rutisson bengt.rutisson at oracle.com
Mon May 14 07:46:39 UTC 2012


Hi again,  :-)

Here is an updated webrev where PrintGCCause is off by default in JDK7 
but on by default in JDK8:
http://cr.openjdk.java.net/~brutisso/7166894/webrev.05/

The relevant change is in arguments.cpp:
http://cr.openjdk.java.net/~brutisso/7166894/webrev.05/src/share/vm/runtime/arguments.cpp.udiff.html

With this proposal there is still one slight change in JDK7 logging. For 
full GCs that were triggered by System.gc() calls we used to log the 
cause. Now this will not happen unless you add -XX:+PrintGCCause. This 
will not break any parsers, but it might make some parsers miss 
System.gc() calls.

I think we are getting closer to wrapping this change up. It is a little 
unclear to me who would like to be listed as reviewers. Could those that 
would like to be reviewers please take a look at the latest webrev and 
let me know.

Thanks,
Bengt


On 2012-05-11 19:51, Srinivas Ramakrishna wrote:
> Mikael, thanks for sounding that note of caution... what you say makes 
> sense.
>
> -- ramki
>
> On Fri, May 11, 2012 at 10:17 AM, Mikael Vidstedt 
> <mikael.vidstedt at oracle.com <mailto:mikael.vidstedt at oracle.com>> wrote:
>
>
>     I'm all for improving the information in the log messages, great
>     work! However, I'm not sure I'm warm and fuzzy about potentially
>     breaking users' log parsers in a minor update. My preference would
>     be to have the PrintGCCause flag be default false in jdk7 and
>     default true in jdk8+. In general I'd prefer to only change the
>     log messages in major releases.
>
>     Reasonable?
>
>     Cheers,
>     Mikael
>
>
>     On 2012-05-11 07:30, Bengt Rutisson wrote:
>>
>>     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/
>>     <http://cr.openjdk.java.net/%7Ebrutisso/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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