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From: Brian Barrett (bbarrett_at_[hidden])
Date: 2007-08-28 12:12:08


On Aug 28, 2007, at 9:05 AM, Li-Ta Lo wrote:

> On Mon, 2007-08-27 at 15:10 -0400, Rolf vandeVaart wrote:
>> We are running into a problem when running on one of our larger SMPs
>> using the latest Open MPI v1.2 branch. We are trying to run a job
>> with np=128 within a single node. We are seeing the following error:
>>
>> "SM failed to send message due to shortage of shared memory."
>>
>> We then increased the allowable maximum size of the shared segment to
>> 2Gigabytes-1 which is the maximum allowed on 32-bit application. We
>> used the mca parameter to increase it as shown here.
>>
>> -mca mpool_sm_max_size 2147483647
>>
>> This allowed the program to run to completion. Therefore, we would
>> like to increase the default maximum from 512Mbytes to 2G-1
>> Gigabytes.
>> Does anyone have an objection to this change? Soon we are going to
>> have larger CPU counts and would like to increase the odds that
>> things
>> work "out of the box" on these large SMPs.
>>
>
>
> There is a serious problem with the 1.2 branch, it does not allocate
> any SM area for each process at the beginning. SM areas are allocated
> on demand and if some of the processes are more aggressive than the
> others, it will cause starvation. This problem is fixed in the trunk
> by assign at least one SM area for each process. I think this is what
> you saw (starvation) and an increase of max size may not be necessary.

Although I'm pretty sure this is fixed in the v1.2 branch already.

I don't think we should raise that ceiling at this point. We create
the file in /tmp, and if someone does -np 32 on a single, small node
(not unheard of), it'll do really evil things.

Personally, I don't think we need nearly as much shared memory as
we're using. It's a bad design in terms of its unbounded memory
usage. We should fix that, rather than making the file bigger. But
I'm not going to fix it, so take my opinion with a grain of salt.

Brian