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Hi John,<br>
<br>
On 2/8/13 7:06 AM, John Cuthbertson wrote:<br>
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Hi Bengt,<br>
<br>
Looks very good. Ship it!.<br>
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<br>
Thanks for looking at this!<br>
<br>
Bengt<br>
<br>
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JohnC<br>
<br>
<div class="moz-cite-prefix">On 2/1/2013 7:10 AM, Bengt Rutisson
wrote:<br>
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Hi all,<br>
<br>
Could I have a couple of reviews for this change?<br>
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<br>
For the evacuation failure handling in G1 we need to store the
mark word for objects that we self-forward. We store these mark
words in two GrowableArrays. The problem is that if we have a
lot of objects that need to be self-forwarded we will add a lot
of entries to the GrowableArrays. These arrays will double in
size when they get full. Worst case these arrays can require
more consecutive free memory than is available in the OS malloc
heap.<br>
<br>
I have a test (ManyObjects) that runs out of native memory on
Windows 32 bit platforms because of this issue. We want to
double from 10MB to 20MB when we hit native out of memory.<br>
<br>
My fix for this will reduce the risk for native out of memory.
Instead of doubling the size I introduce a chunked data
structure that will only malloc one new chunk when it gets full.
This requires less consecutive memory. It also has the nice side
effect that we don't have to copy the entries when we need more
memory.<br>
<br>
Without this fix I get native out of memory about every three
runs of the test. With this fix the test has been running for
several days and more than 5600 iterations.<br>
<br>
The chunk size is variable but has a max limit. I use 40 entries
as initial size since this is what the GrowableArrays used. I
picked
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10000 as the maximum size. The value
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10000 can probably be tuned further, but 100000 was too much (I
still got native OOME) and 10000 works fine.<br>
<br>
I have been comparing GC pause times with and without my fix for
the ManyObjects test. I don't see any large differences in the
pause times. This will only affect performance for runs that
have a lot of evacuation failures. These runs will benefit form
the fact that we don't have to do as much copying as before, but
they will also do several more mallocs compared to before my
fix. The runs I've done indicate that this evens out. I can't
see any large differences.<br>
<br>
Thanks,<br>
Bengt<br>
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