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

[Kim Barrett]

On Jan 7, 2015, at 3:02 PM, Thomas Schatzl <thomas.schatzl 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.

Making the zero-fill block sizes large (e.g. not just a page at a time) might make a
DMA-based memset interesting (when available).  But that’s obviously a much
bigger change again.

> Either way is fine for me.

For fixing this bug, I’m ok with keeping things simple.