Fwd: Re: Solaris specific bug in GC log rotation - extremely long pause

Erik Helin erik.helin at oracle.com
Wed Nov 11 08:49:01 UTC 2015


Hi Rainer,

thanks for the detailed bug report. I'm adding hotspot-runtime-dev,
since this seeems like a runtime issue.

Thanks,
Erik

----- Forwarded message from Rainer Jung <rainer.jung at kippdata.de> -----

> From: Rainer Jung <rainer.jung at kippdata.de>
> To: Poonam Bajaj Parhar <poonam.bajaj at oracle.com>, "hotspot-gc-dev at openjdk.java.net" <hotspot-gc-dev at openjdk.java.net>
> Date: Wed, 11 Nov 2015 08:38:39 +0100
> Subject: Re: Solaris specific bug in GC log rotation - extremely long pause
> 
> Hi Poonam,
> 
> Am 11.11.2015 um 00:05 schrieb Poonam Bajaj Parhar:
> >Hello Rainer,
> >
> >Could you please file a bug for this problem here:
> >http://bugreport.java.com/
> 
> I did right now.
> 
> >Please provide the problem description there and attach the reproducible
> >program, and let us know the created bug id.
> 
> The bug ID is: (Review ID: JI-9026481) - One long Safepoint pause directly
> after each GC log rotation
> 
> I couldn't attach anything, the bug submission forms do not give the
> opportunity to attach files. I copied the Java and shell script sources into
> one of the text boxes, but I couldn't fill in all of the reproduction
> explanations. Please feel free to attach the tar.gz file I had sent to the
> list.
> 
> Thanks for your help and advice!
> 
> Regards,
> 
> Rainer
> 
> >On 11/10/2015 2:15 PM, Rainer Jung wrote:
> >>In case anyone is interested, I'll attach some reproduction code.
> >>You can run it as a standalone Java program on Solaris. It is pretty
> >>small and simple. A README is included.
> >>
> >>I hope the list accepts attachments.
> >>
> >>Regards,
> >>
> >>Rainer
> >>
> >>Am 10.11.2015 um 16:45 schrieb Rainer Jung:
> >>>There's a bug in the Solaris specific HotSpot code which exhibits itself
> >>>as extremely long pauses directly after GC log rotation.
> >>>
> >>>The bug can be seen in 1.7.0 patchlevel 80 and above, 1.8.0 patchlevel
> >>>20 and above and 1.9.0. It was noticed using
> >>>-XX:PrintGCApplicationStoppedTime.
> >>>
> >>>During GC log rotation the function os::print_memory_info() in
> >>>src/os/solaris/vm/os_solaris.cpp is called, which itself calls
> >>>check_addr0().
> >>>
> >>>Now check_addr0() reads the file /proc/self/pmap, but does this entry by
> >>>entry. Productive Java processes often have 1000 and more map entries
> >>>(e.g. each thread stack is one entry, often each jar etc.
> >>>
> >>>Reading one entry takes about 35-40ms in a zone on a T4 system. Reading
> >>>e.g. 1000 entries takes 35-40 seconds during which the JVM is stopped.
> >>>We experienced even stop times up until 2400 seconds in extreme cases.
> >>>
> >>>Note that this doesn't have to do with GC. It only happens directly
> >>>after GC log file rotation.
> >>>
> >>>The bug is reading the file entry by entry instead of using pread() to
> >>>read it in one go. Look for instance at the source code of the Solaris
> >>>command "pmap" which uses pread() to read the file at once.
> >>>
> >>>It might also be questioned, whether this map file check must happen
> >>>during a safepoint or could also be done outside, only synchronizing in
> >>>case a hit was found and a warning actually needs to be written to the
> >>>log file.
> >>>
> >>>The bug was shadowed by another bug until and including 1.7.0_76 and
> >>>1.8.0_11: the close() that closes the map file after reading the entries
> >>>was erroneously put inside the read loop instead of after the read loop.
> >>>Thus these versions only read the first entry, then closed the file and
> >>>erred out when trying to read the next entry. So reading was quick.
> >>>
> >>>The responsible change was:
> >>>
> >>>Java 8:
> >>>http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/diff/7d28f4e15b61/src/os/solaris/vm/os_solaris.cpp
> >>>
> >>>
> >>>
> >>>Java 7:
> >>>http://hg.openjdk.java.net/jdk7u/jdk7u/hotspot/diff/e50eb3195734/src/os/solaris/vm/os_solaris.cpp
> >>>
> >>>
> >>>
> >>>Example code for reading using pread() (going back to OpenSolaris):
> >>>
> >>>https://github.com/joyent/illumos-joyent/blob/master/usr/src/cmd/ptools/pmap/pmap.c
> >>>
> >>>
> >>>
> >>>Look e.g. at function xmapping_iter() and there look for pread().
> >>>
> >>>See also the discussion thread starting at
> >>>http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2015-November/002351.html.
> >>>
> >>>
> >>>
> >>>The analysis was done using source code review and realtime checks with
> >>>pstack and truss. It would be nice if you could instruct me how to get
> >>>this fixed. It is a bit specific because it only happens on Solaris and
> >>>when GC log rotation is active, but Solaris should be an important
> >>>platform for Oracle and GC log rotation will be used more and more.
> >>>
> >>>I do *not* have a support contract.
> >>>
> >>>Regards,
> >>>
> >>>Rainer

----- End forwarded message -----


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