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

[Zhengyu Gu]

Hi Thomas,

On 11/16/2017 04:45 AM, Thomas Stüfe wrote:
> 
> 
> On Thu, Nov 16, 2017 at 10:23 AM, Severin Gehwolf <sgehwolf at redhat.com 
> <mailto:sgehwolf at redhat.com>> wrote:
> 
>     On Thu, 2017-11-16 at 08:14 +0100, Thomas Stüfe wrote:
>     > On Thu, Nov 16, 2017 at 7:58 AM, David Holmes <david.holmes at oracle.com <mailto: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.
> 
>     +1
> 
>     While plaform skew is a valid concern, I'm doubtful it's "unnecessary".
>     I think there is value to get one platform fixed and then look at other
>     platforms one by one as follow-up bugs. For some platforms it might be
>     hard to do (or undesirable) as Thomas says.
> 
>     Thanks,
>     Severin
> 
> 
> I volunteer to implement this for windows if it can be done as
> non-time-critical follow up, if no-one else has stepped up in until then.

I can work on Windows solution today if it helps the case :-)

Thanks,

-Zhengyu


> 
> ..Thomas
> 
> 
>      > 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
>     <https://bugs.openjdk.java.net/browse/JDK-8191369>
>      > > > Webrev:
>     http://cr.openjdk.java.net/~zgu/8191369/webrev.00/index.html
>     <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
>      > > >
>      > > >
> 
>