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Subject: Re: [OMPI devel] SM init failures
From: Ashley Pittman (ashley_at_[hidden])
Date: 2009-04-01 17:12:09


On Tue, 2009-03-31 at 11:00 -0400, Jeff Squyres wrote:
> On Mar 31, 2009, at 3:45 AM, Sylvain Jeaugey wrote:
> > System V shared memory used to be the main way to do shared memory on
> > MPICH and from my (little) experience, this was truly painful :
> > - Cleanup issues : does shmctl(IPC_RMID) solve _all_ cases ? (even
> > kill
> > -9 ?)
> Indeed. The one saving grace here is that the cleanup issues
> apparently can be solved on Linux with a special flag that indicates
> "automatically remove this shmem when all processes attaching to it
> have died." That was really the impetus for [re-]investigating sysv
> shm. I, too, remember the sysv pain because we used it in LAM, too...

Unless there is something newer than IPC_RMID that I haven't heard of
this is far from a complete solution, setting RMID causes it to be
deleted when the attach count becomes zero so it handles the kill -9
case however it has the down side that once it's been set no further
processes can attach to the memory so you have to leave a window during
init during which any crash will leave the memory.

I've always been of the opinion that mmaping shared files was a much
more advanced solution.

Ashley Pittman.