RFR: 8151436: Leaner ArrayAllocator and BitMaps

Per Liden per.liden at oracle.com
Wed Mar 9 15:26:42 UTC 2016

On 2016-03-09 15:28, Stefan Karlsson wrote:
> Hi all,
> I found a bug in the ArrayAllocator code. ArrayAllocator::free
> incorrectly calls should_use_malloc(size_for_malloc(length)) when the
> call should be should_use_malloc(length).
> There is an -XX:+ExecuteInternalVMTests that exercises this code path,
> and try to find these kinds of bugs. The test actually manages to call
> allocate_malloc and then tries to free the memory with free_mmap, but
> the JVM doesn't crash. One reason why it doesn't crash is that
> os::release_memory, which is used by free_mmap, fails to unmap the
> malloced memory and we silently ignores that.
> This patch:
> 1) Adds an assert to ensure that the os::release_memory call succeeds.
> This immediately shows the problem when we execute our internal vm tests.
> 2) Moves the implementation of should_use_malloc to the inline file, so
> that it can reuse size_for_malloc.
> 3) Fix the bug.
> http://cr.openjdk.java.net/~stefank/8151436/webrev.01.delta/
> http://cr.openjdk.java.net/~stefank/8151436/webrev.01/

Looks good.


> Thanks,
> StefanK
> On 2016-03-08 11:33, Stefan Karlsson wrote:
>> Hi all,
>> Please review this patch to remove the state variables from
>> ArrayAllocator and make it an AllStatic class instead. The main
>> motivation for this patch is to cleanup the BitMaps data structure and
>> make the instances smaller.
>> The patch builds on the fact that the current code invokes
>> AllocateHeap with the default value AllocFailEnum:EXIT_OOM, and
>> therefore never returns NULL. This means that use_malloc will never be
>> reset and the allocation strategy used (malloc or mmap) can be
>> determined by simply looking at the size input parameter. Instead of
>> changing the code to use AllocateHeap with AllocFailEnum::RETURN_NULL,
>> I chose to keep the current behavior so that we could cleanup and
>> minimize the size of our BitMaps.
>> http://cr.openjdk.java.net/~stefank/8151436/webrev/
>> https://bugs.openjdk.java.net/browse/JDK-8151436
>> Thanks,
>> StefanK

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