linux-kernel - Re: [patch 3/7] mm: vmscan: clarify how swappiness, highest priority, memcg interact

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Message-ID: <50CF618C.6020100@redhat.com>
Date:	Mon, 17 Dec 2012 13:16:44 -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>,
	Satoru Moriya <satoru.moriya@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/7] mm: vmscan: clarify how swappiness, highest priority,
 memcg interact

On 12/17/2012 01:12 PM, Johannes Weiner wrote:
> A swappiness of 0 has a slightly different meaning for global reclaim
> (may swap if file cache really low) and memory cgroup reclaim (never
> swap, ever).
>
> In addition, global reclaim at highest priority will scan all LRU
> lists equal to their size and ignore other balancing heuristics.
> UNLESS swappiness forbids swapping, then the lists are balanced based
> on recent reclaim effectiveness.  UNLESS file cache is running low,
> then anonymous pages are force-scanned.
>
> This (total mess of a) behaviour is implicit and not obvious from the
> way the code is organized.  At least make it apparent in the code flow
> and document the conditions.  It will be it easier to come up with
> sane semantics later.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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


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