RFR(XS) 8191369: NMT: Enhance thread stack tracking

[Thomas Stüfe]

On Thu, Nov 16, 2017 at 7:58 AM, David Holmes <david.holmes at oracle.com>
wrote:

> Hi Zhengyu,
>
> I can't review this in detail as I'm not familiar with NMT workings, but
> have a couple of comments.
>
> On 16/11/2017 8:25 AM, Zhengyu Gu wrote:
>
>> This is Linux only enhancement for now, can be extended for other
>> platforms. (See bug for details)
>>
>
> I'm concerned about unnecessary platform skew. I added some comments to
> the bug. I think the mincore trick can be used on Solaris and AIX as well -
> but not on OS X / BSD. It may be that VirtualQuery can be used on Windows
> to get the same information - but I'm unclear if the memory states support
> what you're looking for. It would be good to extend this to other platforms
> that will support it.
>

Just 5c:

I think this is definitely useful even with only the Linux implementation
provided.

On AIX we have commit-on-touch and hence mincore may actually force commit
the thread :P - would have to try it but have no high hopes. Well.

On Windows this is possible, we already use VirtualQuery in our fork to
print out the commit-state of the current thread stack in case of an error.

..Thomas


> And on a minor note can you please correct the existing spelling error in
> get_stack_commited_bottom. :)
>
> Current implementation, thread stack is tracked when thread is created,
>> its available stack space is tagged as reserved and committed.
>>
>> However, this is not how stack works. Stack pages are committed on
>> demand, so this approach overstates its memory usage.
>>
>> This enhancement gathers thread stack usage at NMT query time, so that it
>> can report more accurate usage.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8191369
>> Webrev: http://cr.openjdk.java.net/~zgu/8191369/webrev.00/index.html
>>
>>
>> Example:
>>
>> Summary shows thread stacks only use small faction of reserved space.
>>
>> -                    Thread (reserved=41216KB, committed=632KB)
>>                              (thread #41)
>>                              (stack: reserved=41032KB, committed=448KB)
>>                              (malloc=137KB #222)
>>                              (arena=47KB #76)
>>
>>
>> Detail tracking shows stack guards and actually used/committed stack area.
>>
>> [0x00007f66e95e7000 - 0x00007f66e96e8000] reserved 1028KB for Thread
>> Stack from
>>      [0x00007f67c0b57d5c] JavaThread::run()+0x2c
>>      [0x00007f67c08bbea2] thread_native_entry(Thread*)+0x112
>>
>>          [0x00007f66e95e7000 - 0x00007f66e95eb000] committed 16KB from
>>              [0x00007f67c08b7319] os::pd_create_stack_guard_pages(char*,
>> unsigned long)+0x29
>>              [0x00007f67c0b56851] JavaThread::create_stack_guard_pages()
>> [clone .part.125]+0xa1
>>              [0x00007f67c0b57d6e] JavaThread::run()+0x3e
>>              [0x00007f67c08bbea2] thread_native_entry(Thread*)+0x112
>>
>>          [0x00007f66e96e7000 - 0x00007f66e96e8000] committed 4KB
>>
>
> Can we capture this in a test so we can tell that the tracking has
> improved?
>
> Thanks,
> David
> -----
>
> Thanks,
>>
>> -Zhengyu
>>
>>