linux-kernel - Re: [PATCH 20/31] sched, numa, mm/mpol: Make mempolicy home-node aware

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Message-ID: <20121101135813.GX3888@suse.de>
Date:	Thu, 1 Nov 2012 13:58:13 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 20/31] sched, numa, mm/mpol: Make mempolicy home-node
 aware

On Thu, Oct 25, 2012 at 02:16:37PM +0200, Peter Zijlstra wrote:
> Add another layer of fallback policy to make the home node concept
> useful from a memory allocation PoV.
> 
> This changes the mpol order to:
> 
>  - vma->vm_ops->get_policy	[if applicable]
>  - vma->vm_policy		[if applicable]
>  - task->mempolicy
>  - tsk_home_node() preferred	[NEW]
>  - default_policy
> 
> Note that the tsk_home_node() policy has Migrate-on-Fault enabled to
> facilitate efficient on-demand memory migration.
> 

Makes sense and it looks like a VMA policy, if set, will still override
the home_node policy as you'd expect. At some point this may need to cope
with node hot-remove. Also, at some point this must be dealing with the
case where mbind() is called but the home_node is not in the nodemask.
Does that happen somewhere else in the series? (maybe I'll see it later)

-- 
Mel Gorman
SUSE Labs
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