linux-kernel - Re: [PATCH -mm] vmscan: bail out of page reclaim after swap_cluster

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Message-Id: <20081117093832.f383bd61.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 17 Nov 2008 09:38:32 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Rik van Riel <riel@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mm] vmscan: bail out of page reclaim after
 swap_cluster_max pages

On Sun, 16 Nov 2008 16:38:56 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> One more point.
> 
> > Sometimes the VM spends the first few priority rounds rotating back
> > referenced pages and submitting IO.  Once we get to a lower priority,
> > sometimes the VM ends up freeing way too many pages.
> > 
> > The fix is relatively simple: in shrink_zone() we can check how many
> > pages we have already freed and break out of the loop.
> > 
> > However, in order to do this we do need to know how many pages we already
> > freed, so move nr_reclaimed into scan_control.
> 
> IIRC, Balbir-san explained the implemetation of the memcgroup 
> force cache dropping feature need non bail out at the past reclaim 
> throttring discussion.
> 
> I am not sure about this still right or not (iirc, memcgroup implemetation
> was largely changed).
> 
> Balbir-san, Could you comment to this patch?
> 
> 
I'm not Balbir-san but there is no "force-cache-dropping" feature now.
(I have no plan to do that.)

But, mem+swap controller will need to modify reclaim path to do "cache drop
first" becasue the amount of "mem+swap" will not change when "mem+swap" hit
limit. It's now set "sc.may_swap" to 0.

Hmm, I hope memcg is a silver bullet to this kind of special? workload in
long term.


Thanks,
-Kame



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