Date: Sat, 14 Mar 2009 23:29:05 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may get wrongly discarded
Cc: kosaki.motohiro@jp.fujitsu.com, Peter Zijlstra <peterz@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       David Howells <dhowells@redhat.com>, torvalds@linux-foundation.org,
       Enrik.Berkhan@ge.com, uclinux-dev@uclinux.org,
       linux-kernel@vger.kernel.org
In-Reply-To: <20090313104442.GB2119@cmpxchg.org>
References: <20090313170058.6840.A69D9226@jp.fujitsu.com> <20090313104442.GB2119@cmpxchg.org>
Message-Id: <20090314232411.4495.A69D9226@jp.fujitsu.com>
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> > (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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