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Subject: Re: [OMPI devel] SM init failures
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-04-01 18:58:38


IIRC, we certainly used to unlink the file after init. Are you sure
somebody changed that?

On Apr 1, 2009, at 4:29 PM, Jeff Squyres wrote:

> So everyone hates SYSV. Ok. :-)
>
> Given that part of the problems we've been having with mmap have
> been due to filesystem issues, should we just unlink() the file once
> all processes have mapped it? I believe we didn't do that
> originally for two reasons:
>
> - leave it around for debugging purposes
> - possibly supporting MPI-2 dynamics someday
>
> We still don't support the sm BTL for dynamics, so why not
> unlink()? (I'm probably forgetting something obvious...?)
>
>
>
> On Apr 1, 2009, at 5:12 PM, Ashley Pittman wrote:
>
>> 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.
>>
>> _______________________________________________
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>> devel_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>
>
> --
> Jeff Squyres
> Cisco Systems
>
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