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Hi Coleen, <br>
<br>
Thanks for looking at this!<br>
<br>
On 4/25/13 1:54 PM, Coleen Phillimore wrote:<br>
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Hi Bengt,<br>
My memory was that all that weird code for aligning windows mmap
space was for CDS. Can you try your test with -Xshare:dump and
-Xshare:on -version?<br>
thanks,<br>
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<br>
Seems to work:<br>
<br>
>hotspot.exe -Xshare:dump<br>
Using java runtime at: d:\java\jdk-7-fcs-bin-b148\jre<br>
Loading classes to share ... done.<br>
Rewriting and linking classes ... done.<br>
Number of classes 2245<br>
Calculating fingerprints ... done.<br>
Removing unshareable information ... done.<br>
ro space: 7132288 [ 36.9% of total] out of 16777216 bytes [42.5%
used] at 0x0000000800000000<br>
rw space: 10270832 [ 53.2% of total] out of 16777216 bytes [61.2%
used] at 0x0000000801000000<br>
md space: 1881528 [ 9.7% of total] out of 4194304 bytes [44.9%
used] at 0x0000000802000000<br>
mc space: 34053 [ 0.2% of total] out of 122880 bytes [27.7%
used] at 0x0000000802400000<br>
total : 19318701 [100.0% of total] out of 37871616 bytes [51.0%
used]<br>
<br>
>hotspot.exe -Xshare:on -version<br>
Using java runtime at: d:\java\jdk-7-fcs-bin-b148\jre<br>
java version "1.7.0"<br>
Java(TM) SE Runtime Environment (build 1.7.0-b148)<br>
Java HotSpot(TM) 64-Bit Client VM (build 25.0-b30-internal-debug,
mixed mode, sharing)<br>
<br>
<br>
I have also run JPRT on my change and I think that does some CDS
testing, right?<br>
<br>
Thanks,<br>
Bengt<br>
<br>
<blockquote cite="mid:5179196E.9060801@oracle.com" type="cite">
<div class="moz-cite-prefix"> Coleen<br>
<br>
On 4/25/2013 7:09 AM, Bengt Rutisson wrote:<br>
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<br>
Hi everyone,<br>
<br>
Could I have a couple of reviews of this change?<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Ebrutisso/8012915/webrev.00/">http://cr.openjdk.java.net/~brutisso/8012915/webrev.00/</a><br>
<br>
Background from the CR:<br>
<br>
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The method ReservedSpace::align_reserved_region() does not work
on Windows. It tries to free parts of the previously allocated
memory by doing two calls to os::release_memory(). However, on
Windows os::release_memory() is implemented as: <br>
<br>
VirtualFree(addr, 0, MEM_RELEASE) <br>
<br>
which will always free up all the allocated memory: <br>
<br>
<a moz-do-not-send="true"
href="http://msdn.microsoft.com/en-gb/library/windows/desktop/aa366892%28v=vs.85%29.aspx">http://msdn.microsoft.com/en-gb/library/windows/desktop/aa366892%28v=vs.85%29.aspx</a>
<br>
<br>
"The function frees the entire region that is reserved in the
initial allocation call to VirtualAlloc." <br>
<br>
This means that if ReservedSpace::align_reserved_region() is
executed on Windows and we try to trim the beginning of the
memory that we had allocated we will free all of the allocated
memory. Subsequent calls to os::commit_memory() which will end
up as: <br>
<br>
VirtualAlloc(addr, bytes, MEM_COMMIT, PAGE_READWRITE) <br>
<br>
will fail with 487, ERROR_INVALID_ADDRESS - Attempt to access
invalid address. <br>
<br>
The solution is to use the existing method
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os::reserve_memory_aligned() which does the same thing but works
on all platforms.<br>
<br>
I assume that it is unusual that we enter this code path since I
haven't seen a lot of crashes that seem related to this issue.
But when we tried a patch that plays a bit with the alignments
we crash on Windows. To have a simple reproducer I added a unit
test. The test is not 100% fool proof, but on Windows without my
proposed fix it fails 999 times out of 1000 runs. With my fix it
passes 100% of the time.<br>
<br>
Thanks,<br>
Bengt<br>
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