linux-kernel - Re: [PATCH 2/3] Properly account for the number of page cache pages zone

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Message-Id: <20090609175211.DD85.A69D9226@jp.fujitsu.com>
Date:	Tue,  9 Jun 2009 17:55:03 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Wu Fengguang <fengguang.wu@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	"linuxram@...ibm.com" <linuxram@...ibm.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] Properly account for the number of page cache pages zone_reclaim() can reclaim

> > > The ideal would be that the number of tmpfs pages would also be known
> > > and account for like NR_FILE_MAPPED as swap is required to discard them.
> > > A means of working this out quickly was not obvious but a comment is added
> > > noting the problem.
> > 
> > I'd rather prefer it be accounted separately than to muck up NR_FILE_MAPPED :)
> > 
> 
> Maybe I used a poor choice of words. What I meant was that the ideal would
> be we had a separate count for tmpfs pages. As tmpfs pages and mapped pages
> both have to be unmapped and potentially, they are "like" each other with
> respect to the zone_reclaim_mode and how it behaves. We would end up
> with something like
> 
> 	pagecache_reclaimable -= zone_page_state(zone, NR_FILE_MAPPED);
> 	pagecache_reclaimable -= zone_page_state(zone, NR_FILE_TMPFS);

Please see shmem_writepage(). tmpfs writeout make swapcache, We also
need to concern swapcache.

note: swapcache also increase NR_FILE_PAGES, see add_to_swap_cache.



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