from space and to space size is different and varies

[Thomas Rohde]

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.

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
>> _______________________________________________
>> hotspot-gc-use mailing list
>> hotspot-gc-use at openjdk.java.net
>> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use


-- 
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Thomas Rohde
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