linux-kernel - Re: [PATCH 5/7] mm: page_alloc: Make zone distribution page aging policy configurable

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Date:	Mon, 16 Dec 2013 14:25:49 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] mm: page_alloc: Make zone distribution page aging
 policy configurable

On 12/13/2013 09:10 AM, Mel Gorman wrote:
> Commit 81c0a2bb ("mm: page_alloc: fair zone allocator policy") solved a
> bug whereby new pages could be reclaimed before old pages because of
> how the page allocator and kswapd interacted on the per-zone LRU lists.
> Unfortunately it was missed during review that a consequence is that
> we also round-robin between NUMA nodes. This is bad for two reasons
> 
> 1. It alters the semantics of MPOL_LOCAL without telling anyone
> 2. It incurs an immediate remote memory performance hit in exchange
>    for a potential performance gain when memory needs to be reclaimed
>    later
> 
> No cookies for the reviewers on this one.
> 
> This patch makes the behaviour of the fair zone allocator policy
> configurable.  By default it will only distribute pages that are going
> to exist on the LRU between zones local to the allocating process. This
> preserves the historical semantics of MPOL_LOCAL.
> 
> By default, slab pages are not distributed between zones after this patch is
> applied. It can be argued that they should get similar treatment but they
> have different lifecycles to LRU pages, the shrinkers are not zone-aware
> and the interaction between the page allocator and kswapd is different
> for slabs. If it turns out to be an almost universal win, we can change
> the default.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Acked-by: Rik van Riel <riel@...hat.com>


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