G1 eden resizing behaviour ?

[Yu Zhang]

Simone,

Please see my comments in line.

Thanks,
Jenny

On 12/9/2014 6:26 AM, Simone Bordet wrote:
> Hi,
>
> On Tue, Dec 9, 2014 at 3:06 PM, Thomas Schatzl
> <thomas.schatzl at oracle.com> wrote:
>> This may be because the heap is already very full (around
>> 100-G1ReservePercent) so it cuts down on the young gen size.
>>
>> G1 tries to keep G1ReservePercent of heap empty to avoid evacuation
>> failure.
> It's not my case: I have a 32 GiB heap with a permanent live set of
> about 5-6 GiB, so I should have plenty of space even with a 15 GiB or
> so eden, which is what I typically see as max eden size.
Can you add -XX:+PrintAdaptiveSizePolicy and share your logs?  I was 
guessing the same, that the heap is full.  The mixed gc might not clean 
all the garbage.  Even though the live data set is 5-6 GB, the heap can 
still be close to full.
>
>> Another reason could be that G1 thinks that the pauses caused by marking
>> cut too much into the available time budget (depending on your
>> settings), so it decreases the heap.
> You mean by the remark, which is STW ?
> Indeed I have very long remark pauses (up to 2.5s), apparently caused
> by weak reference processing.
>
> I need to investigate this issue, as the application itself does not
> use them (perhaps some library ?).
> There is a big difference between the references processed in the
> remark phase (3 millions) and those processed during a young GC (less
> than a thousand).
>
> Am I correct assuming that those processed during remark only belong
> to tenured ?
I agree.  Do you have -XX:+ParallelRefProcEnabled?  This will help 
reducing the refproc time, but 3 millions is a lot.
>
> Thanks !
>