To: Jamie Lokier <jamie@shareable.org>
Cc: Pavel Machek <pavel@ucw.cz>,
       =?iso-8859-1?q?J=F6rn?= Engel <joern@wohnheim.fh-wedel.de>, mj@ucw.cz,
       jack@ucw.cz, "Patrick J. LoPresti" <patl@users.sourceforge.net>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cowlinks v2
References: <20040320152328.GA8089@wohnheim.fh-wedel.de>
	<20040329171245.GB1478@elf.ucw.cz> <s5g7jx31int.fsf@patl=users.sf.net>
	<20040329231635.GA374@elf.ucw.cz>
	<20040402165440.GB24861@wohnheim.fh-wedel.de>
	<20040402180128.GA363@elf.ucw.cz>
	<20040402181707.GA28112@wohnheim.fh-wedel.de>
	<20040402182357.GB410@elf.ucw.cz>
	<20040402200921.GC653@mail.shareable.org>
	<20040402213933.GB246@elf.ucw.cz>
	<20040403010425.GJ653@mail.shareable.org>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: 03 Apr 2004 11:39:53 -0700
In-Reply-To: <20040403010425.GJ653@mail.shareable.org>
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Jamie Lokier <jamie@shareable.org> writes:

> Here's a tricky situation:
> 
>    1. A file is cowlinked.  Then each cowlink is mmap()'d, one per process.
> 
>    2. At this point both mappings share the same pages in RAM.

Why they have different inodes?  
 
>    3. Then one of the cowlinks is written to...

I would not worry about sharing page cache entries unless this becomes
a common case.  If you want to avoid the hit of rereading the file when
you have a cow copy it should be simple enough to walk through the list
of cow copies and see if anyone else has it open.

Eric
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