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Subject: Re: [OMPI devel] System V Shared Memory for Open MPI: Request forCommunity Input and Testing
From: Barrett, Brian W (bwbarre_at_[hidden])
Date: 2010-06-11 12:53:50


On Jun 11, 2010, at 5:10 AM, Jeff Squyres wrote:

> On Jun 11, 2010, at 5:43 AM, Paul H. Hargrove wrote:
>
>>> Interesting. Do you think this behavior of the linux kernel would
>>> change if the file was unlink()ed after attach ?
>>
>> As Jeff pointed out, the file IS unlinked by Open MPI, presumably to
>> ensure it is not left behind in case of abnormal termination.
>
> I have to admit that I lied. :-(
>
> Sam and I were talking on the phone yesterday about the shm_open() stuff and to my chagrin, I discovered that the mmap'ed files are *not* unlinked in OMPI until MPI_FINALIZE. I'm not actually sure why; I could have sworn that we unlinked them after everyone mmap'ed them...

The idea was one large memory segment for all processes and it wasn't unlinked after complete attach so that we could have spawned procs also use shmem (which never worked, of course). So I think we could unlink during init at this point..

Brian

--
  Brian W. Barrett
  Dept. 1423: Scalable System Software
  Sandia National Laboratories