About the location of data structure and its inner objects

Krystal Mok rednaxelafx at gmail.com
Wed Aug 28 07:09:29 PDT 2013


Thanks Thomas. I missed that G1 defaults to adaptively sizing the logical
generations.

- Kris


On Wed, Aug 28, 2013 at 9:32 PM, Thomas Schatzl
<thomas.schatzl at oracle.com>wrote:

> Hi,
>
> On Wed, 2013-08-28 at 16:42 +0800, Krystal Mok wrote:
> > Hi Lijie,
> >
> > On Wed, Aug 28, 2013 at 10:46 AM, Lijie Xu <csxulijie at gmail.com>
> > wrote:
> >         Thank Tao, I think I have a graph of memory layout now. I have
> >         another five questions:
> >
>
> >         1) Can old space's max size be adjusted dynamically by GC
> >         while the JVM is running?
> >
> > Yes if you're using UseParallelGC / UseParallelOldGC and
> > UseAdaptiveSizePolicy is on (it is on by default). Other GCs in
> > HotSpot don't implement adaptive size policy yet.
>
> G1 too: In G1 the old gen is simply what is left over from the young gen
> mostly sized by pause time and total available memory.
>
> >         3) Whether MinorGC can copy an object directly into Old if the
> >         Survior hasn't enough space to hold it currently?
> >
> > Yes, it could. That would be called a "premature promotion" /
> > "survivor space overflow".
> > It is even possible to directly allocate a new object in the old
> > generation. Assuming you can read Chinese, refer to this thread for an
> > example: http://hllvm.group.iteye.com/group/topic/38293
>
> This typically affects very large objects (large depending on the
> collector, e.g. too large to fit into the young generation). They are
> allocated directly into the old generation.
>
> Hth,
>   Thomas
>
>
>
>
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