RFR(S): 8010738: G1: Output for full GCs with +PrintGCDetails should contain perm gen size/meta data change info

Srinivas Ramakrishna ysr1729 at gmail.com
Wed May 15 20:18:31 UTC 2013

To keep it consistent with what we've always had on hotspot (and which is how I was interpreting the output here -- never having looked too closely at recent logging changes), I'd suggest staying with:-

Used before -- > used after (capacity after)

Don't know if this is consistent with what's the normal today, but that's what it has been for spaces in the past. Capacity after has usually been interpreted as committed rather than reserved. The former is a more generally useful measure in my experience, compared with the more static latter measure.

Bernd makes some good points that one might want to keep in mind as these evolve.

-- Ramki


On May 15, 2013, at 12:33, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:

> John and I talked about it.  I had not known that with perm the information
> printed was (used, capacity, reserved).  At one point I had been printing
> all 4 for metaspace and breaking GC parsers along the way.  What seems
> like the right thing?
> Jon
> On 5/15/2013 10:28 AM, John Cuthbertson wrote:
>> Hi Ramki,
>> Sorry for the late response. The bug will take a couple of days before it's visible.
>> I didn't realize it was a bug. My impression was that you had to keep track of how the values change between GCs because I can see how all three values (used, capacity, reserved) would be useful.
>> JohnC
>> On 5/14/2013 11:40 PM, Srinivas Ramakrishna wrote:
>>> ah, thanks Jon! (i am guessing the CR will become visible eventually
>>> on bugs.sun.com? Or should I be looking elsewhere?)
>>> On Tue, May 14, 2013 at 10:23 AM, Jon Masamitsu
>>> <jon.masamitsu at oracle.com> wrote:
>>>> On 5/13/13 5:40 PM, Srinivas Ramakrishna wrote:
>>>>> Hi John --
>>>>> On Mon, May 6, 2013 at 3:23 PM, John Cuthbertson
>>>>> <john.cuthbertson at oracle.com> wrote:
>>>>>>> 4.896: [Full GC (Allocation Failure) 512M->343M(512M), 4.3640117 secs]
>>>>>>>     [Eden: 0.0B(25.0M)->0.0B(97.0M) Survivors: 0.0B->0.0B Heap:
>>>>>>> 512.0M(512.0M)->343.3M(512.0M)], [Metaspace: 1611K->2433K(6448K)]
>>>>>>>   [Times: user=5.13 sys=0.15, real=4.36 secs]
>>>>>> The information that gets printed mirrors that of the other collectors.
>>>>>> Here's parallel GC:
>>>>>>> 33.245: [Full GC (Ergonomics) [PSYoungGen: 133632K->3423K(144640K)]
>>>>>>> [ParOldGen: 348158K->348158K(348160K)] 481790K->351581K(492800K),
>>>>>>> [Metaspace: 1612K->2433K(6448K)], 2.5788089 secs] [Times: user=9.96
>>>>>>> sys=0.00, real=2.58 secs]
>>>>>> The information that's printed is the amount of metaspace used before the
>>>>>> GC, the capacity, and the amount of reserved space.
>>>>> Do you know why the "used after" for the metadataspace increased after
>>>>> the full gc?
>>>>> Is that normal, common, rare or abnormal ? :-)
>>>> I think that is a bug.  The "capacity" should be "used" after GC .
>>>> CR is 8014546.
>>>> Thanks.
>>>> Jon
>>>> Jon
>>>>> thanks John!
>>>>> -- ramki

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