hsperfdata causing long GC/safepoint times: Don't use mmap?

Dmitry Samersoff dmitry.samersoff at oracle.com
Thu Mar 26 17:54:03 UTC 2015


What filesystem do you use for /tmp ?

Did you try to reproduce the problem with tmpfs?


On 2015-03-26 18:14, Evan Jones wrote:
> At Twitter, I recently discovered that the hsperfdata file that is created
> by default by the JVM causes long safepoint and GC pauses. It turns out
> that writes to mmap-ed files can block until disk I/O completes, even if
> the I/O is to another disk. For details see:
> http://www.evanjones.ca/jvm-mmap-pause.html
> We have been experimenting with adding the -XX:+PerfDisableSharedMem JVM
> flag on a number of our latency sensitive services, and have seen a
> significant improvement. Our JVM team (which I am *not* part of), is
> investigating potential changes to the JVM to prevent this.
> Any suggestions for an approach to solving this problem that could be
> accepted into Hotspot itself? Some options:
> * Make the location of this file configurable (this was set with
> java.io.tmpdir for a time, but then was reverted; see
> http://bugs.java.com/view_bug.do?bug_id=6447182)
> * Use shared memory that is not backed by a file?
> * Something else I'm not considering?
> Thanks!
> Evan Jones

Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.

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