linux-kernel - Re: [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy

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Message-ID: <20160617120703.GN1868@techsingularity.net>
Date:	Fri, 17 Jun 2016 13:07:03 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy

On Fri, Jun 17, 2016 at 01:27:09PM +0200, Vlastimil Babka wrote:
> On 06/09/2016 08:04 PM, Mel Gorman wrote:
> >The fair zone allocation policy interleaves allocation requests between
> >zones to avoid an age inversion problem whereby new pages are reclaimed
> >to balance a zone. Reclaim is now node-based so this should no longer be
> >an issue and the fair zone allocation policy is not free. This patch
> >removes it.
> 
> I wonder if fair zone allocation had the side effect of preventing e.g. a
> small Normal zone to be almost fully occupied by long-lived unreclaimable
> allocations early in the kernel lifetime. So that might be one thing to
> watch out for.

It's a marginal corner case and the zonelist scan is slightly inefficient
as the first zone is always skipped but the impact is light.

> But otherwise I would agree it should be no longer needed
> with node-based reclaim.
> 
> >Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 

Thanks.

-- 
Mel Gorman
SUSE Labs