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

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Date:	Fri, 7 Mar 2008 18:14:56 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <clameter@....com>
cc:	Paul Jackson <pj@....com>, akpm@...ux-foundation.org,
	Lee.Schermerhorn@...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 Fri, 7 Mar 2008, Christoph Lameter wrote:

> And where is the patch to set the system (or cpuset....) default policy? 
> ;-)
> 

The system default policy is inherently defined in get_vma_policy() and 
alloc_pages_current().

> Note that the system default policy changes during bootup. Could that be 
> done with the default policy? We had some issues a while back with 
> processes spawned at boot inheriting the interleave policy. If they could 
> refer to default_policy instead then a change of default_policy would 
> switch all spawned processes to use MPOL_DEFAULT?
> 

With the patch, get_vma_policy() would return the VMA's policy if it has 
its own get_policy() function that returns a valid policy or differs from 
the default, otherwise it would refer to whatever default_policy is 
statically allocated to represent.

For task mempolicies, alloc_pages_current() has always used default_policy 
if current->mempolicy is NULL.  So you can change default_policy.policy to 
be anything you want (and its v.nodes or v.preferred_node members) and 
that will be the effected policy for any task that doesn't have a valid 
->mempolicy.
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