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 18:17:05 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [uClinux-dev] RE: [PATCH] NOMMU: Pages allocated to a ramfs 
	inode's pagecache may get wrongly discarded

On Fri, Mar 13, 2009 at 4:56 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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.
>

I agree as Andrew pointed out.
It may be workaround but can be a good solution in current status.
And then, we have to improve it for removal of ramfs pages from lru
list in future, I think.

-- 
Kinds regards,
Minchan Kim
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