RFR: 8062063: Usage of UseHugeTLBFS, UseLargePagesInMetaspace and huge SurvivorAlignmentInBytes cause crashes in CMBitMapClosure::do_bit

Kim Barrett kim.barrett at oracle.com
Wed Jan 7 23:12:28 UTC 2015

On Jan 7, 2015, at 5:50 PM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
>>> mking the scan for pages that need to be cleared and their clearing
>>> chunkier by using BitMap::get_next_[zero,one]_offset to search for
>>> ranges that need to be cleared?  It makes the code a little more
>>> complicated than the present bit at a time iteration, but is probably
>>> faster if there are long runs in the bitmap, which seems plausible,
>>> but should probably be tested.  But it might not be worth doing if
>>> performance isn't important here.
>> It would be a nice addition, but I do not feel it is required for this
>> particular bug fix. As you mention, it is slightly more complicated. The
>> overhead seems small compared to the effort to zero-fill a large page.
> I agree that this would probably improve the clearing but for this fix I would prefer to leave it as is. The goal is to get this fix backported into 8u40 and therefore I would prefer to avoid adding more complexity.

Agreed.  So the change looks good to me.

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