[torqueusers] vmem and pvmem

[Martin Siegert]

On Fri, Feb 24, 2012 at 11:19:37AM +0100, "Mgr. Šimon Tóth" wrote:
> > Core_req       vmem  pvmem ulimit-v RPT
> > =========================================
> > nodes=1:ppn=2  1gb   256mb 256mb    512mb
> > procs=2        1gb   256mb 256mb    1gb
> > nodes=1:ppn=2  1gb   4gb   1gb      4gb
> > procs=2        1gb   4gb   1gb      4gb
> > nodes=1:ppn=2  1gb   -     1gb      512mb
> > procs=2        1gb   -     1gb      1gb
> >
> > So the ulimit value that influences whether a task can allocate
> > memory, is set as the lower of the vmem and pvmem values. That
> > makes some sense - at least more sense than taking the larger
> > value.  What doesn't make sense is allowing pvmem to be higher
> > than vmem in the first place - in that case torque should probably
> > reject the job or 'fix' one of the settings but leaving it as is
> > might not be so bad, except for moab's behaviour (keep reading).
> 
> No. The logic is as follows:
> 
> * if pvmem (or pmem) is set
>    then set the corresponding ulimit to pvmem (pmem) value
> 
> * if pvmem (or pmem) isn't set
>    then set the corresponding ulimit to vmem (mem) value
> 
> Note that using pvmem is mostly pointless. On Linux this represents 
> address space, not virtual memory.
> 
> You can use vmem as virtual memory, but even that is extremely confusing.

I do not understand this comment. Both pvmem and vmem requests will
result in RLIMIT_AS getting set.
When I submit a MPI job using, e.g., procs=N, why is requesting
pvmem=X mostly pointless? Shouldn't it be totally equivalent to
requesting vmem=X*N ?

Cheers,
Martin