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Subject: [OMPI devel] Potential Performance issues with mmap'ed files
From: Tim Mattox (tmattox_at_[hidden])
Date: 2013-08-22 11:13:40


Hello Open MPI developers,
I've been away from the Open MPI code for a long time now, but I just
ran across this article that should give developers second thoughts
about using mmap'ed files in performance critical situations.

"Deferring mtime and ctime updates"
http://lwn.net/SubscriberLink/564120/bdc189d08c512761/

I might suggest an audit of the Open MPI code base for mmap calls
to make sure they are all needed, or if they can be done
a different way, especially in the coll and sm btl.
Yes, the article is about a patchset to lessen the performance problem,
but until that gets into the kernel, and into the distributions, and into
the parallel machines, this could be a source of lost performance in Open MPI.

I seem to recall some work was done after I left development to
make use of POSIX or SYSV shared memory system calls that avoided
having an associated backing-store file. But I don't remember if
those became the default, or if mmap'ed files was still the default.

Anyway, back to lurking on the mailing lists for me.
P.S. - Darn, my timattox_at_[hidden] e-mail alias is gone... c'est la vie!

-- 
Tim Mattox, Ph.D. - tmattox_at_[hidden]