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

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Message-ID: <20121218100449.GK9887@suse.de>
Date:	Tue, 18 Dec 2012 10:04:50 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>, 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 Mon, Dec 17, 2012 at 01:12:33PM -0500, 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>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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