RFR (S): JDK-6348447 - Specifying -XX:OldSize crashes 64-bit VMs

Vitaly Davidovich vitalyd at gmail.com
Tue Jan 15 13:32:30 UTC 2013

Hi Jesper,

Is NewRatio guaranteed to be non-zero when used inside


Sent from my phone
On Jan 15, 2013 8:11 AM, "Jesper Wilhelmsson" <jesper.wilhelmsson at oracle.com>

> Jon,
> Thank you for looking at this! I share your concerns and I have moved the
> knowledge about policies to CollectorPolicy. set_heap_size() now simply
> asks the collector policy if it has any recommendations regarding the heap
> size.
> Ideally, since the code knows about young and old generations, I guess the
> new function "recommended_heap_size()" should be placed in
> GenCollectorPolicy, but then the code would have to be duplicated for G1 as
> well. However, CollectorPolicy already know about OldSize and NewSize so I
> think it is OK to put it there.
> Eventually I think that we should reduce the abstraction level in the
> generation policies and merge CollectorPolicy, GenCollectorPolicy and maybe
> even TwoGenerationCollectorPolicy and if possible G1CollectorPolicy, so I
> don't worry too much about having knowledge about the two generations in
> CollectorPolicy.
> A new webrev is available here:
> http://cr.openjdk.java.net/~**jwilhelm/6348447/webrev.2/<http://cr.openjdk.java.net/~jwilhelm/6348447/webrev.2/>
> Thanks,
> /Jesper
> On 2013-01-14 19:00, Jon Masamitsu wrote:
>> Jesper,
>> I'm a bit concerned that set_heap_size() now knows about how
>> the CollectorPolicy uses OldSize and NewSize.   In the distant
>> past set_heap_size() did not know what kind of collector was
>> going to be used and probably avoided looking at those
>> parameters for that reason.  Today we know that a generational
>> collector is to follow but maybe you could hide that knowledge
>> in CollectorPolicy somewhere and have set_heap_size() call into
>> CollectorPolicy to use that information?
>> Jon
>> On 01/14/13 09:10, Jesper Wilhelmsson wrote:
>>> Hi,
>>> I would like a couple of reviews of a small fix for JDK-6348447 -
>>> Specifying -XX:OldSize crashes 64-bit VMs
>>> Webrev:
>>> http://cr.openjdk.java.net/~**jwilhelm/6348447/webrev/<http://cr.openjdk.java.net/~jwilhelm/6348447/webrev/>
>>> Summary:
>>> When starting HotSpot with an OldSize larger than the default heap size
>>> one will run into a couple of problems. Basically what happens is that the
>>> OldSize is ignored because it is incompatible with the heap size. A debug
>>> build will assert since a calculation on the way results in a negative
>>> number, but since it is a size_t an if(x<0) won't trigger and the assert
>>> catches it later on as incompatible flags.
>>> Changes:
>>> I have made two changes to fix this.
>>> The first is to change the calculation in TwoGenerationCollectorPolicy::
>>> **adjust_gen0_sizes so that it won't result in a negative number in the
>>> if statement. This way we will catch the case where the OldSize is larger
>>> than the heap size and adjust the OldSize instead of the young size. There
>>> are also some cosmetic changes here. For instance the argument
>>> min_gen0_size is actually used for the old generation size which was a bit
>>> confusing initially. I renamed it to min_gen1_size (which it already was
>>> called in the header file).
>>> The second change is in Arguments::set_heap_size. My reasoning here is
>>> that if the user sets the OldSize we should probably adjust the heap size
>>> to accommodate that OldSize instead of complaining that the heap is too
>>> small. We determine the heap size first and the generation sizes later on
>>> while initializing the VM. To be able to fit the generations if the user
>>> specifies sizes on the command line we need to look at the generation size
>>> flags a little already when setting up the heap size.
>>> Thanks,
>>> /Jesper
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