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<div class="moz-cite-prefix">On 06/26/2013 01:57 PM, Bengt Rutisson
wrote:<br>
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<blockquote cite="mid:51CAD73B.7040201@oracle.com" type="cite">
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<br>
Hi all,<br>
<br>
Could I have a couple of reviews for this really small change?<br>
<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Ebrutisso/8017483/webrev.00/">http://cr.openjdk.java.net/~brutisso/8017483/webrev.00/</a><br>
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<br>
Looks good.<br>
<br>
StefanK<br>
<br>
<blockquote cite="mid:51CAD73B.7040201@oracle.com" type="cite"> <br>
Background:<br>
<br>
For JDK-8012265 I increased the default value for
HeapBaseMinAddress on Solaris x86 from 256m to 1g when using G1.
In that change I used
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FLAG_SET_ERGO() to set the new value of HeapBaseMinAddress. Now it
turns out that there is code that checks
!FLAG_IS_DEFAULT(HeapBaseMinAddress), which means that by setting
the flag as "ergo" I changed the behavior of the VM.<br>
<br>
What happens is that Universe::preferred_heap_base() will use
exactly the address HeapBaseMinAddress if it is not default.
Otherwise it will calculate a base adress "backwards" from the
maximum compressed oops heap size and the desired heap size. The
effect is that if HeapBaseMinAddress=1g as default and we want a
16g heap we will get an actual heap base of at about address 16g.
But if I set HeapBaseMinAddress=1g on the command line or using
"ergo" we will pick the address 1g for the heap base.<br>
<br>
This means that in the first case we leave almost 16g free for the
Solaris C-heap, but in the second case the C-heap will be limited
to 1g.<br>
<br>
I think this is a strange behavior and I will file a separate bug
to track that. There are also other issues with the compressed
oops set up. But to make the currently failing tests pass I
suggest to change from "ergo" to "default" when updating the
HeapBaseMinAddress value. This is small, quick and safe change.
Here is the complete diff:<br>
<br>
diff --git a/src/share/vm/runtime/arguments.cpp
b/src/share/vm/runtime/arguments.cpp<br>
--- a/src/share/vm/runtime/arguments.cpp<br>
+++ b/src/share/vm/runtime/arguments.cpp<br>
@@ -1571,7 +1571,7 @@<br>
// By default HeapBaseMinAddress is 2G on all platforms
except Solaris x86.<br>
// G1 currently needs a lot of C-heap, so on Solaris we have
to give G1<br>
// some extra space for the C-heap compared to other
collectors.<br>
- FLAG_SET_ERGO(uintx, HeapBaseMinAddress, 1*G);<br>
+ FLAG_SET_DEFAULT(HeapBaseMinAddress, 1*G);<br>
}<br>
}<br>
<br>
Thanks,<br>
Bengt<br>
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