linux-kernel - Re: [patch -mm 2/2] mempolicy: use default_policy mode instead of MPOL

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Message-ID: <alpine.DEB.1.00.0803081414460.12095@chino.kir.corp.google.com>
Date:	Sat, 8 Mar 2008 14:20:14 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
cc:	Paul Jackson <pj@....com>, akpm@...ux-foundation.org,
	clameter@....com, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch -mm 2/2] mempolicy: use default_policy mode instead of
 MPOL_DEFAULT

On Sat, 8 Mar 2008, Lee Schermerhorn wrote:

> I have a patch queued up, waiting for things to settle down in
> mempolicy.c, to replace the policy/mode in default_policy with
> MPOL_PREFERRED with preferred_node = -1.  Then, we can remove all of the
> MPOL_DEFAULT cases out of the switches in the allocation paths and
> "clean up" the documentation, including man pages.  MPOL_DEFAULT becomes
> simply an API mechanism to request fall back to the surrounding policy
> scope which, to my mind, is what "default policy" means.
> 

Ok, I'll await your patch that switches default_policy.policy to 
MPOL_PREFERRED.

Using MPOL_DEFAULT purely for falling back to the task or system-wide 
policy, however, seems confusing.  The semantics seem to indicate that 
MPOL_DEFAULT represents the system-wide default policy without any 
preferred node or set of nodes to bind or interleave.  So if a VMA has a 
policy of MPOL_DEFAULT then, to me, it seems like that indicates the 
absence of a specific policy, not a mandate to fallback to the task 
policy.
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