linux-kernel - Re: [PATCH] mm: evict streaming IO cache first

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Date:	Mon, 17 Nov 2008 08:22:13 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [PATCH] mm: evict streaming IO cache first

On Mon, 17 Nov 2008, KAMEZAWA Hiroyuki wrote:
> 
> How about resetting zone->recent_scanned/rotated to be some value calculated from
> INACTIVE_ANON/INACTIVE_FILE at some time (when the system is enough idle) ?

.. or how about just considering the act of adding a new page to the LRU 
to be a "scan" event? IOW, "scanning" is not necessarily just an act of 
the VM looking for pages to free, but would be a more general "activity" 
meter.

IOW, when we calculate the percentages of anon-vs-file in get_scan_ratio() 
we take into account how much anon-page activity vs how much file cache 
activity there has been.

So if we've seen a lot of filesystem activity ("streaming"), we would tend 
to prefer to scan the page cache. If we've seen a lot of anon page 
mapping, we'd tend to prefer to scan the anon side.

That would seem to be the right kind of thing to do: if we literally have 
a load that only does streaming and pages never get moved to the active 
LRU, it should basically keep the page cache close to constant size - 
which is just another way of saying that we should only be scanning page 
cache pages.

Hmm? 

			Linus
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