linux-kernel - Re: [patch 7/8] mm: vmscan: compaction works against zones, not lruvecs

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Date:	Wed, 12 Dec 2012 17:31:42 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 7/8] mm: vmscan: compaction works against zones, not lruvecs

On 12/12/2012 04:43 PM, Johannes Weiner wrote:
> The restart logic for when reclaim operates back to back with
> compaction is currently applied on the lruvec level.  But this does
> not make sense, because the container of interest for compaction is a
> zone as a whole, not the zone pages that are part of a certain memory
> cgroup.
>
> Negative impact is bounded.  For one, the code checks that the lruvec
> has enough reclaim candidates, so it does not risk getting stuck on a
> condition that can not be fulfilled.  And the unfairness of hammering
> on one particular memory cgroup to make progress in a zone will be
> amortized by the round robin manner in which reclaim goes through the
> memory cgroups.  Still, this can lead to unnecessary allocation
> latencies when the code elects to restart on a hard to reclaim or
> small group when there are other, more reclaimable groups in the zone.
>
> Move this logic to the zone level and restart reclaim for all memory
> cgroups in a zone when compaction requires more free pages from it.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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

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