linux-kernel - Re: [patch 3/3] cpusets: add memory_spread

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Date:	Fri, 26 Oct 2007 11:00:43 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Paul Jackson <pj@....com>
cc:	Lee Schermerhorn <Lee.Schermerhorn@...com>, rientjes@...gle.com,
	akpm@...ux-foundation.org, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 3/3] cpusets: add memory_spread_user option

On Fri, 26 Oct 2007, Paul Jackson wrote:

> > Will it handle the case of MPOL_INTERLEAVE policy on a shm segment that
> > is mapped by tasks in different, possibly disjoint, cpusets.  Local
> > allocation does, and my patch does.  That was one of the primary
> > goals--to address an issue that Christoph has with shared policies.
> > cpusets really muck these up!
> 
> It probably won't handle that.  I don't get along too well with shmem.

IMHO shmem policy support is pretty much messed up (seems that we 
introduced new races by trying to fix the refcounts). I tend to ignore the 
stuff unless it impacts regular shared or regular memory. Before we do any 
of this fancy stuff lets at least get the refcount handling right?

> Can you to an anti-shmem bigot how MPOL_INTERLEAVE should work with
> shmem segments mapped in diverse ways by different tasks in different
> cpusets?  What would be the key attribute(s) of a proper solution?
> Maybe if we keep it simple enough, I can avoid mucking it up too much
> this time around.

With relative nodemasks we could have a MPOL_INTERLEAVE policy working in 
multiple cpuset contexts. If nodes 0 and 1 are set in a nodemask then the 
first two nodes of the current cpuset are interleaved through. Nodes that 
do not exist are ignored. So if there is no second node then 
MPOL_INTERLEAVE becomes a noop.
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