linux-kernel - Re: [patch 2/2] cpusets: add interleave_over

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Message-ID: <alpine.DEB.0.9999.0710261436140.16966@chino.kir.corp.google.com>
Date:	Fri, 26 Oct 2007 14:39:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
cc:	Paul Jackson <pj@....com>, clameter@....com,
	akpm@...ux-foundation.org, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] cpusets: add interleave_over_allowed option

On Fri, 26 Oct 2007, Lee Schermerhorn wrote:

> So, you pass the subset, you don't set the flag to indicate you want
> interleaving over all available.  You must be thinking of some other use
> for saving the subset mask that I'm not seeing here.  Maybe restoring to
> the exact nodes requested if they're taken away and then re-added to the
> cpuset?
> 

Paul's motivation for saving the passed nodemask to set_mempolicy() is so 
that the _intent_ of the application is never lost.  That's the biggest 
advantage that this method has and that I totally agree with.  So whenever 
the mems_allowed of a cpuset changes, the MPOL_INTERLEAVE nodemask of all 
attached tasks becomes their intent (pol->passed_nodemask) AND'd with the 
new mems_allowed.  That can be done on mpol_rebind_policy() and shouldn't 
be an extensive change.

So MPOL_INTERLEAVE, and possibly other, mempolicies will always try to 
accomodate the intent of the application but only as far as the task's 
cpuset restriction allows them.

		David
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