linux-kernel - Re: [PATCH] mm, vmscan: Make kswapd reclaim no more than needed

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Message-ID: <20160624093226.GE1868@techsingularity.net>
Date:	Fri, 24 Jun 2016 10:32:26 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Hillf Danton <hillf.zj@...baba-inc.com>
Cc:	'Johannes Weiner' <hannes@...xchg.org>,
	'Vlastimil Babka' <vbabka@...e.cz>,
	'linux-kernel' <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm, vmscan: Make kswapd reclaim no more than needed

On Fri, Jun 24, 2016 at 04:59:55PM +0800, Hillf Danton wrote:
> We stop reclaiming pages if any eligible zone is balanced.
> 
> Signed-off-by: Hillf Danton <hillf.zj@...baba-inc.com>

wakeup_kswapd avoids waking kswapd in the first place if there are balanced
zones. The current code will do at least one reclaim pass if the situation
changes between the wakeup request and kswapd actually waking so some
progress will be made. The risk for strict enforcement is that small low
zones like DMA will be quickly generally balanced but only for very short
periods of time and kswapd will fall behind. It *shouldn't* matter as
the pages allocated from DMA will remain resident until the full node
LRU cycles through but it's a possibility.

I'll test the patch and make sure kswapd still reclaims at the correct
rate. Did you this test yourself with any reclaim intensive workload to
see if kswapd fell behind forcing more stalls in direct reclaim?

-- 
Mel Gorman
SUSE Labs