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

John Cuthbertson john.cuthbertson at oracle.com
Mon May 14 19:00:10 UTC 2012


Hi Bengt,

Overall this looks good to me, but I do have a couple of minor comments 
and questions....

arguments.cpp - Typo @ line 3096

gcCause.hpp - fields in the new class should have a leading underscore.

g1CollectedHeap.cpp - @ line 3600. IMO using a local to hold the GC 
string and pass that into the TraceTime constructor would improve the 
readability significantly.

g1CollectorPolicy.cpp - @ line 888. If you have a log level == finer, 
where is the print of the date/timestamp prefix now?

Other than that, it looks good?

JohnC

On 05/14/12 00:46, Bengt Rutisson wrote:
>
> 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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