linux-kernel - Re: [PATCH] mm, numa: Sanitize task_numa

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Message-ID: <20130731112510.GS2296@suse.de>
Date:	Wed, 31 Jul 2013 12:25:10 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, numa: Sanitize task_numa_fault() callsites

On Thu, Jul 25, 2013 at 12:38:45PM +0200, Peter Zijlstra wrote:
> 
> Subject: mm, numa: Sanitize task_numa_fault() callsites
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Jul 22 10:42:38 CEST 2013
> 
> There are three callers of task_numa_fault():
> 
>  - do_huge_pmd_numa_page():
>      Accounts against the current node, not the node where the
>      page resides, unless we migrated, in which case it accounts
>      against the node we migrated to.
> 
>  - do_numa_page():
>      Accounts against the current node, not the node where the
>      page resides, unless we migrated, in which case it accounts
>      against the node we migrated to.
> 
>  - do_pmd_numa_page():
>      Accounts not at all when the page isn't migrated, otherwise
>      accounts against the node we migrated towards.
> 
> This seems wrong to me; all three sites should have the same
> sementaics, furthermore we should accounts against where the page
> really is, we already know where the task is.
> 

Agreed. To allow the scheduler parts to still be evaluated in proper
isolation I moved this patch to much earlier in the series.

-- 
Mel Gorman
SUSE Labs
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