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

[Mikael Vidstedt]

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/
>
> 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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