Optimizing card table scanning in CMS collector

[Alexey Ragozin]

Hi,

Recently I was analyzing CMS  GC pause times on JVM with 32Gb of heap (using
Oracle Coherence node as sample application). It seems like young collection
pause time is totally dominated by time required to scan card table (I
suppose size of table should be 64Mb in this case). I believe time to scan
card table could be cut significantly at price of slightly more complex
write-barrier. By introducing super-cards collector can avoid scanning whole
ranges of card table. I would like to implement POC to prove reduction of
young collection pause (also it should probably reduce CMS remark pause
time).

I need an advice to locate right places for modification in code base (I’m
not familiar with it). I thing I can ignore JIT for sake of POC (running JVM
in interpreter mode). So I need to modify write barrier used in interpreter
and card table scanning procedure.


Thank you for advice.
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