linux-kernel - Re: [PATCH] RFC: vmscan: add min_filelist_kbytes sysctl for protecting the working set

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Message-ID: <20101103154249.GA1779@barrios-desktop>
Date:	Thu, 4 Nov 2010 00:42:49 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, wad@...omium.org,
	olofj@...omium.org, hughd@...omium.org
Subject: Re: [PATCH] RFC: vmscan: add min_filelist_kbytes sysctl for
 protecting the working set

On Wed, Nov 03, 2010 at 07:41:35AM -0400, Rik van Riel wrote:
> On 11/02/2010 11:03 PM, Minchan Kim wrote:
> 
> >It could.
> >But time based approach would be same, IMHO.
> >First of all, I don't want long latency of direct reclaim process.
> >It could affect response of foreground process directly.
> >
> >If VM limits the number of pages reclaimed per second, direct reclaim
> >process's latency will be affected. so we should avoid throttling in
> >direct reclaim path. Agree?
> 
> The idea would be to not throttle the processes trying to
> reclaim page cache pages, but to only reclaim anonymous
> pages when the page cache pages are low (and occasionally
> a few page cache pages, say 128 a second).

Fair enough. Only anon reclaim is better than thrashing of code pages. 

> 
> If too many reclaimers come in when the page cache is
> low and no swap is available, we will OOM kill instead
> of stalling.

I understand why you use (file < pages_min).
We can keep the threshold small value. Otherwise, 
we can see the many OOM question. "Why OOM happens although my system have enough 
file LRU pages?"

> 
> After all, the entire point of this patch would be to
> avoid minutes-long latencies in triggering the OOM
> killer.

I got your point. The patch's goal is not protect working set fully, but prevent
page cache thrashing in low file LRU. 
It could make minutes-long latencies by reaching the OOM. 

Okay. I will look into this idea.
Thanks for the good suggestion, Rik. 

> 
> -- 
> All rights reversed

-- 
Kind regards,
Minchan Kim
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