linux-kernel - Re: [RFC] high system time & lock contention running large mixed workload

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Message-Id: <1259685662.2345.11.camel@dhcp-100-19-198.bos.redhat.com>
Date:	Tue, 01 Dec 2009 11:41:02 -0500
From:	Larry Woodman <lwoodman@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC] high system time & lock contention running large mixed
	workload

On Tue, 2009-12-01 at 21:23 +0900, KOSAKI Motohiro wrote:
> (cc to some related person)

> 
> At first look,
> 
>    - We have to fix this issue certenally.
>    - But your patch is a bit risky. 
> 
> Your patch treat trylock(pte-lock) failure as no accessced. but
> generally lock contention imply to have contention peer. iow, the page
> have reference bit typically. then, next shrink_inactive_list() move it
> active list again. that's suboptimal result.
> 
> However, we can't treat lock-contention as page-is-referenced simply. if it does,
> the system easily go into OOM.
> 
> So, 
> 	if (priority < DEF_PRIORITY - 2)
> 		page_referenced()
> 	else
> 		page_refenced_trylock()
> 
> is better?
> On typical workload, almost vmscan only use DEF_PRIORITY. then,
> if priority==DEF_PRIORITY situation don't cause heavy lock contention,
> the system don't need to mind the contention. anyway we can't avoid
> contention if the system have heavy memory pressure.
> 


Agreed.  The attached updated patch only does a trylock in the
page_referenced() call from shrink_inactive_list() and only for
anonymous pages when the priority is either 10, 11 or
12(DEF_PRIORITY-2).  I have never seen a problem like this with active
pagecache pages and it does not alter the existing shrink_page_list
behavior.  What do you think about this???





View attachment "pageout.diff" of type "text/x-patch" (6797 bytes)