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Subject: Re: [OMPI devel] SM init failures
From: Tim Mattox (timattox_at_[hidden])
Date: 2009-03-30 13:40:27


I've been lurking on this conversation, and I am again left with the impression
that the underlying shared memory configuration based on sharing a file
is flawed. Why not use a System V shared memory segment without a
backing file as I described in ticket #1320?

On Mon, Mar 30, 2009 at 1:34 PM, George Bosilca <bosilca_at_[hidden]> wrote:
> Then it looks like the safest solution is the use either ftruncate or the
> lseek method and then touch the first byte of all memory pages.
> Unfortunately, I see two problems with this. First, there is a clear
> performance hit on the startup time. And second, we will have to find a
> pretty smart way to do this or we will completely break the memory affinity
> stuff.
>
>  george.
>
> On Mar 30, 2009, at 13:24 , Iain Bason wrote:
>
>>
>> On Mar 30, 2009, at 12:05 PM, Jeff Squyres wrote:
>>
>>> But don't we need the whole area to be zero filled?
>>
>> It will be zero-filled on demand using the lseek/touch method.  However,
>> the OS may not reserve space for the skipped pages or disk blocks.  Thus one
>> could still get out of memory or file system full errors at arbitrary
>> points.  Presumably one could also get segfaults from an mmap'ed segment
>> whose pages couldn't be allocated when the demand came.
>>
>> Iain
>>
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>
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-- 
Tim Mattox, Ph.D. - http://homepage.mac.com/tmattox/
 tmattox_at_[hidden] || timattox_at_[hidden]
    I'm a bright... http://www.the-brights.net/