RFR (S): 8134631: G1DummyRegionsPerGC fires assert of assert(words <= filler_array_max_size()) failed: too big for a single object
sangheon.kim at oracle.com
Wed Nov 11 20:35:30 UTC 2015
After discussion with Tom, I decided to add simple fix for this
New change is changing filler limitation(_filler_array_max_size) when
G1DummyRegionsPerGC is used and restore after the use.
On 11/09/2015 04:16 PM, sangheon.kim wrote:
> Hi Tom,
> Thank you for looking at this!
> On 11/09/2015 01:30 PM, Tom Benson wrote:
>> On 11/9/2015 4:10 PM, Tom Benson wrote:
>>> Hi Sangheon,
>>> Rather than changing all the product-version uses, couldn't you
>>> change _filler_array_max_size to
>>> _humongous_object_threshold_in_words around the special debug-only
>>> call to fill_with_object instead?
>> Whoops - Meant to say... change it to HeapRegion::GrainWords. This
>> (testing-only, debug) code already assumes fill_with_object can
>> handle an object that large.
>>> I think it would be better to have the special-case hack there in
>>> the testing code (only used when the G1DummyRegionsPerGC option is
>>> specified). Then you don't need the new alternate entry point and
>>> only change g1CollectedHeap.cpp.
> Well, we can hack here. :)
> And I also have a concern of whether is it worth to change codes for
> debug only test option or not.
> However, I thought there's no reason of adding size limitation for G1
> We are using non-humongous fillers for now but it would be nice to
> have humongous filler as well.
>>> I'm not sure the objects allocate_dummy_regions creates really MUST
>>> be humongous - its stated purpose is just to "artificially expand
>>> the heap by allocating a number of dead regions." But it would
>>> take more changes to allocate_dummy_regions to allocate regions and
>>> then fill with non-humongous objects, possibly not worth it for this
> Yes, we would write filler with non-humongous objects but as we
> already have CollectedHeap::fill_with_xxxx(), it would be better
> utilizing them.
>>> On 11/9/2015 2:28 PM, sangheon.kim wrote:
>>>> Hi all,
>>>> Can I get some reviews for this change for fixing this assert?
>>>> Previous patch(8042668: GC Support for shared heap ranges in CDS)
>>>> limited _filler_array_max_size of G1CollectedHeap to be less than
>>>> humongous threshold.
>>>> And this change led this assert as this flag is trying to fill the
>>>> rest of regions with humongous object.
>>>> As a fix, I removed the limitation to allow humongous filler and
>>>> added a wrapper function, fill_with_non_humongous_objects().
>>>> And replace it with current fill_with_object().
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