G1 feedback: frantic GC cycles

[Igor Veresov]

On 4/30/11 1:38 AM, Simone Bordet wrote:
> Hi,
>
> On Sat, Apr 30, 2011 at 09:04, Igor Veresov<igor.veresov at oracle.com>  wrote:
>> This is pretty weird. Simone, could you run it with -XX:+PrintHeapAtGC, it
>> would be nice to see how big the survivor spaces are.
>
> Ok.
>
>> It seems like at the time a collection happens there is only one young region.
>
> Can I ask how do you know that ? From the logs ?

Actually I was mistaken it's not always like that, but there one 
instance. These are the sizes at the end of the four consequent collections:
[ 518M->517M(1024M)]
[ 518M->517M(1024M)]
[ 518M->518M(1024M)]
[ 519M->518M(1024M)]

It does look like we've filled about 1M before the next collection 
happened, which is the default size of a region. PrintHeapAtGC should 
give more details on how many regions are there in each portion of the heap.

igor