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

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Date:	Fri, 13 Mar 2009 08:56:25 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Jamie Lokier <jamie@...reable.org>,
	uClinux development list <uclinux-dev@...inux.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [uClinux-dev] RE: [PATCH] NOMMU: Pages allocated to a ramfs
 inode's pagecache may get wrongly discarded

On Fri, 2009-03-13 at 08:20 +0900, Minchan Kim wrote:

> > > Does the vm pageout logic include or skip these "dirty" pages looking
> > > for candidates to flush to storage?  What about with MMU?
> > 
> > Includes them, regular pageout will try to do the writeout to clean them
> > and then discard them. 
> > 
> > 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.
> 
> It ins't true any more. 
> UNEVICTABLE_LRU will move ramfs's page from LRU to unevictable list.
> Couldn't we solve this problem if NOMMU can support CONFIG_UNEVICTABLE_LRU ?

That's more of a band-aid than a solution, no? They should never have
been on the list to begin with.

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