RFR (M): 8012915: ReservedSpace::align_reserved_region() broken on Windows

[Bengt Rutisson]

Hi Coleen,

Thanks for looking at this!

On 4/25/13 1:54 PM, Coleen Phillimore wrote:
>
> Hi Bengt,
> 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?
> thanks,

Seems to work:

 >hotspot.exe -Xshare:dump
Using java runtime at: d:\java\jdk-7-fcs-bin-b148\jre
Loading classes to share ... done.
Rewriting and linking classes ... done.
Number of classes 2245
Calculating fingerprints ... done.
Removing unshareable information ... done.
ro space:   7132288 [ 36.9% of total] out of  16777216 bytes [42.5% 
used] at 0x0000000800000000
rw space:  10270832 [ 53.2% of total] out of  16777216 bytes [61.2% 
used] at 0x0000000801000000
md space:   1881528 [  9.7% of total] out of   4194304 bytes [44.9% 
used] at 0x0000000802000000
mc space:     34053 [  0.2% of total] out of    122880 bytes [27.7% 
used] at 0x0000000802400000
total   :  19318701 [100.0% of total] out of  37871616 bytes [51.0% used]

 >hotspot.exe -Xshare:on -version
Using java runtime at: d:\java\jdk-7-fcs-bin-b148\jre
java version "1.7.0"
Java(TM) SE Runtime Environment (build 1.7.0-b148)
Java HotSpot(TM) 64-Bit Client VM (build 25.0-b30-internal-debug, mixed 
mode, sharing)


I have also run JPRT on my change and I think that does some CDS 
testing, right?

Thanks,
Bengt

> Coleen
>
> On 4/25/2013 7:09 AM, Bengt Rutisson wrote:
>>
>> Hi everyone,
>>
>> Could I have a couple of reviews of this change?
>> http://cr.openjdk.java.net/~brutisso/8012915/webrev.00/
>>
>> Background from the CR:
>>
>> 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:
>>
>>  VirtualFree(addr, 0, MEM_RELEASE)
>>
>> which will always free up all the allocated memory:
>>
>> http://msdn.microsoft.com/en-gb/library/windows/desktop/aa366892%28v=vs.85%29.aspx 
>>
>>
>> "The function frees the entire region that is reserved in the initial 
>> allocation call to VirtualAlloc."
>>
>> 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:
>>
>> VirtualAlloc(addr, bytes, MEM_COMMIT, PAGE_READWRITE)
>>
>> will fail with 487, ERROR_INVALID_ADDRESS - Attempt to access invalid 
>> address.
>>
>> The solution is to use the existing method 
>> os::reserve_memory_aligned() which does the same thing but works on 
>> all platforms.
>>
>> 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.
>>
>> Thanks,
>> Bengt
>

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