<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<br>
Hi all,<br>
<br>
Could I have a couple of reviews for this change?<br>
<a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/~brutisso/8002144/webrev.00/">http://cr.openjdk.java.net/~brutisso/8002144/webrev.00/</a><br>
<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
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
10000 as the maximum size. The value
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
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>
</body>
</html>