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

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Message-Id: <20090314232411.4495.A69D9226@jp.fujitsu.com>
Date:	Sat, 14 Mar 2009 23:29:05 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Peter Zijlstra <peterz@...radead.org>,
	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

> > (1) page migration code depend on the page stay on lru.
> > (2) "taking off at reclaim time" can avoid adding lock to fastpath.
> >     anyway, complely removing from lru need something lock.
> >     we disliked it at that time.
> 
> Agreed with (1).  NOMMU can't support migration, though.  But keeping
> them off the LRU on NOMMU needs adjustment of the page cache
> read/write code in mm/filemap.c.

yes.

> I'm not quite sure I understand (2).  But never adding these pages on
> the LRU means we never have to remove them anywhere, no?

Yeah, you are right.
I was confused to munlock/shm_unlock case.



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