from space and to space size is different and varies

[Thomas Rohde]

Hey together!

Thanks for explaining.

Bye,
Thomas


Am 29.10.2012 15:46, schrieb Jon Masamitsu:
>
> On 10/26/2012 1:32 AM, Thomas Rohde wrote:
>> Hi Charlie,
>>
>> thanks for your reply. I could reproduce this with
>> -XX:+UseAdaptiveSizePolicy and Java 1.7.
>>
>> My misbelief that from space and to space are always the same size.
>> Thought that -XX:+UseAdaptiveSizePolicy would change both of them in the
>> same manner.
> UseAdaptiveSizePolicy changes them both at the same time if it
> can.  Excuse the ascii art.
>
> +==========+
> |unused area|
> +==========+
> | from-space|
> +==========+
> | to-space  |
> +==========+
> | eden      |
> +==========+
>
> The space for expansion is above from-space.  from-space
> typically has live data in it.  from-space can be expanded into
> the unused area but to-space cannot (the live data in
> from-space has to stay where it is).  After the next collection
> the roles of from-space and to-space are switched and
> the "new" from-space (the former to-space) can be expanded into
>    the unused area. This means it takes a collections or two for an
> expansion to
> take effect.  It could have been done other ways.  This is how
> it is currently done.
>
> Jon
>
>
>
>> Thanks!
>> Thomas
>>
>>
>> Am 25.10.2012 14:23, schrieb Charlie Hunt:
>>> Hi Thomas,
>>>
>>> It is common for Parallel GC, and Parallel Old GC to adjust survivor sizes when -XX:+UseAdaptiveSizePolicy is enabled.  And, -XX:+UseAdaptiveSizePolicy is enabled by default with either -XX:+UseParallelGC and -XX:+UseParallelOldGC, (iirc, the latter is not available in a Java 5 HotSpot VM).
>>>
>>> If you disable adaptive size policy, via -XX:-UseAdaptiveSizePolicy, survivor sizes should remain the same size.
>>>
>>> hths,
>>>
>>> charlie ...
>>>
>>> On Oct 25, 2012, at 3:47 AM, Thomas Rohde wrote:
>>>
>>>> Hi Folks,
>>>>
>>>> up to yesterday I always thought, that from-space and to-space have
>>>> always the same size. In a GC log of a colleague I saw the following and
>>>> was wondering about it:
>>>>
>>>> 22.10.2012 00:01:59 {Heap before gc invocations=590:
>>>> 22.10.2012 00:01:59  PSYoungGen      total 72768K, used 70928K
>>>> [0xcdc00000, 0xd3800000, 0xf8800000)
>>>> 22.10.2012 00:01:59   eden space 54528K, 100% used
>>>> [0xcdc00000,0xd1140000,0xd1140000)
>>>> 22.10.2012 00:01:59   from space 18240K, 89% used
>>>> [0xd1460000,0xd2464168,0xd2630000)
>>>> 22.10.2012 00:01:59   to   space 18048K, 0% used
>>>> [0xd2660000,0xd2660000,0xd3800000)
>>>> 22.10.2012 00:01:59  PSOldGen        total 1400832K, used 334889K
>>>> [0x78400000, 0xcdc00000, 0xcdc00000)
>>>> 22.10.2012 00:01:59   object space 1400832K, 23% used
>>>> [0x78400000,0x8cb0a778,0xcdc00000)
>>>> 22.10.2012 00:01:59  PSPermGen       total 20480K, used 19997K
>>>> [0x74400000, 0x75800000, 0x78400000)
>>>> 22.10.2012 00:01:59   object space 20480K, 97% used
>>>> [0x74400000,0x75787568,0x75800000)
>>>> 22.10.2012 00:01:59 299113.923: [GC [PSYoungGen: 70928K->15357K(72512K)]
>>>> 405818K->350331K(1473344K), 0.0717791 secs]
>>>> 22.10.2012 00:01:59 Heap after gc invocations=590:
>>>> 22.10.2012 00:01:59  PSYoungGen      total 72512K, used 15357K
>>>> [0xcdc00000, 0xd3800000, 0xf8800000)
>>>> 22.10.2012 00:01:59   eden space 54464K, 0% used
>>>> [0xcdc00000,0xcdc00000,0xd1130000)
>>>> 22.10.2012 00:01:59   from space 18048K, 85% used
>>>> [0xd2660000,0xd355f7d8,0xd3800000)
>>>> 22.10.2012 00:01:59   to   space 18112K, 0% used
>>>> [0xd14a0000,0xd14a0000,0xd2650000)
>>>> 22.10.2012 00:01:59  PSOldGen        total 1400832K, used 334973K
>>>> [0x78400000, 0xcdc00000, 0xcdc00000)
>>>> 22.10.2012 00:01:59   object space 1400832K, 23% used
>>>> [0x78400000,0x8cb1f778,0xcdc00000)
>>>> 22.10.2012 00:01:59  PSPermGen       total 20480K, used 19997K
>>>> [0x74400000, 0x75800000, 0x78400000)
>>>> 22.10.2012 00:01:59   object space 20480K, 97% used
>>>> [0x74400000,0x75787568,0x75800000)
>>>> 22.10.2012 00:01:59 }
>>>>
>>>> Before GC from space has 18240K and to space has 18048K.
>>>> After GC from space has 18048K and to space has 18112K.
>>>>
>>>> java version "1.5.0_20"
>>>> Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_20-b02)
>>>> Java HotSpot(TM) Server VM (build 1.5.0_20-b02, mixed mode)
>>>>
>>>> 1. Why is the size of from space and to space not equal?
>>>> 2. Why is the size always changing?
>>>>
>>>> Bye,
>>>> Thomas
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>>>> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
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-- 
Dipl.-Wirt. Inf. (FH)
Thomas Rohde
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