linux-kernel - Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may get wrongly discarded

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Message-Id: <1236931036.5188.80.camel@laptop>
Date:	Fri, 13 Mar 2009 08:57:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	torvalds@...ux-foundation.org, Enrik.Berkhan@...com,
	uclinux-dev@...inux.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache
 may get wrongly discarded

On Fri, 2009-03-13 at 11:03 +0900, KOSAKI Motohiro wrote:
> Hi
> 
> > > Which as Peter points out:
> > > 
> > > 	The ramfs stuff is rather icky in that it adds the pages to the aging
> > > 	list, marks them dirty, but does not provide a writeout method. 
> > > 
> > > 	This will make the paging code scan over them (continuously) trying to
> > > 	clean them, failing that (lack of writeout method) and putting them back
> > > 	on the list.
> > > 
> > > Not requiring the pages to be added to the LRU would be a really good idea.
> > > They are not discardable, be it in MMU or NOMMU mode, except when the inode
> > > itself is discarded.
> > 
> > Yep, these pages shouldn't be on the LRU at all.  I guess that will
> > require some tweaks to core filemap.c code.
> 
> IMHO, UNEVICTABLE_LRU already does lru isolation.
> only rest prblem is, getting rid of "depends on MMU" line in mm/Kconfig.
> 
> Am I missing anything?

Yes, the need to take something off that shouldn't be there to begin
with.

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