linux-kernel - Re: [PATCH 3/3] mm, mem-hotplug: update pcp->stat

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Message-Id: <20110412193407.B52F.A69D9226@jp.fujitsu.com>
Date:	Tue, 12 Apr 2011 19:34:14 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 3/3] mm, mem-hotplug: update pcp->stat_threshold when memory hotplug occur

> > No good stat_threshold might makes performance hurt.
> 
> Yes. That's I want it.
> My intention is that if you write down log fully, it can help much
> newbies to understand the patch in future and it would be very clear
> Andrew to merge it.
> 
> What I want is following as.
> ==
> 
> Currently, memory hotplug doesn't updates pcp->stat_threashold.
> Then, It ends up making the wrong stat_threshold and percpu_driftmark.
> 
> It could make confusing zoneinfo or overhead by frequent draining.
> Even when memory is low and kswapd is awake, it can mismatch between
> the number of real free pages and vmstat NR_FREE_PAGES so that it can
> result in the livelock. Please look at aa4548403 for more.
> 
> This patch solves the issue.
> ==

Now, wakeup_kswapd() are using zone_watermark_ok_safe(). (ie avoid to use
per-cpu stat jiffies). Then, I don't think we have livelock chance.
Am I missing something?



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