From: Jamie Lokier <jamie@shareable.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Pavel Machek" <pavel@ucw.cz>,
"Jörn 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
Date: Sat, 3 Apr 2004 20:43:44 +0100 [thread overview]
Message-ID: <20040403194344.GA5477@mail.shareable.org> (raw)
In-Reply-To: <m1n05soqh2.fsf@ebiederm.dsl.xmission.com>
Eric W. Biederman wrote:
> > 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?
Did you miss the last 20 or so messages in this thread?
We'd like cowlinks that are an invisible filesystem optimisation.
That means you "copy" a file and it behaves the same as if you copy a file.
> > 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.
It is not a question of performance, it's correctness. Either you
have cowlinks that behave like copied files, or you accept that when
cowlinked files are mmapped and written to, they don't behave like
regular files (not even the original file prior to cowlinking does).
Btw, I'm not suggesting sharing page cache entries.
-- Jamie
next prev parent reply other threads:[~2004-04-03 19:43 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-20 8:34 [PATCH] cowlinks v2 Jörn Engel
2004-03-20 8:49 ` Andrew Morton
2004-03-20 11:27 ` Jörn Engel
2004-03-20 19:28 ` Andrew Morton
2004-03-21 12:43 ` Jörn Engel
2004-03-21 18:53 ` Jörn Engel
[not found] ` <mit.lcs.mail.linux-kernel/20040320083411.GA25934@wohnheim.fh-wedel.de>
2004-03-20 15:03 ` Patrick J. LoPresti
2004-03-20 15:23 ` Jörn Engel
2004-03-29 17:12 ` Pavel Machek
2004-03-29 21:05 ` Patrick J. LoPresti
2004-03-29 23:16 ` Pavel Machek
2004-03-31 14:34 ` Jamie Lokier
2004-03-31 14:45 ` Pavel Machek
2004-03-31 15:20 ` Jamie Lokier
2004-04-02 11:44 ` Tim Connors
2004-04-02 16:54 ` Jörn Engel
2004-04-02 18:01 ` Pavel Machek
2004-04-02 18:17 ` Jörn Engel
2004-04-02 18:23 ` Pavel Machek
2004-04-02 19:28 ` Ross Biro
2004-04-02 21:35 ` Pavel Machek
2004-04-05 8:12 ` Jörn Engel
2004-04-05 8:19 ` Pavel Machek
2004-04-05 8:45 ` Jörn Engel
2004-04-02 20:09 ` Jamie Lokier
2004-04-02 21:39 ` Pavel Machek
2004-04-02 22:00 ` Chris Friesen
2004-04-03 0:49 ` Jamie Lokier
2004-04-03 8:23 ` Pavel Machek
2004-04-03 13:15 ` Jamie Lokier
2004-04-05 8:19 ` Jörn Engel
2004-04-05 8:22 ` Pavel Machek
2004-04-03 0:46 ` Jamie Lokier
2004-04-03 1:04 ` Jamie Lokier
2004-04-03 1:21 ` Erik Andersen
2004-04-03 1:59 ` Jamie Lokier
2004-04-03 3:55 ` Ross Biro
2004-04-03 9:09 ` Pavel Machek
2004-04-03 13:27 ` Jamie Lokier
2004-04-03 18:39 ` Eric W. Biederman
2004-04-03 19:43 ` Jamie Lokier [this message]
2004-04-03 20:30 ` Eric W. Biederman
2004-04-03 21:59 ` Jamie Lokier
2004-04-04 8:15 ` Eric W. Biederman
2004-04-05 8:35 ` Jörn Engel
2004-04-05 9:15 ` Eric W. Biederman
2004-04-05 9:18 ` Jörn Engel
2004-04-05 11:43 ` Pavel Machek
2004-04-05 12:17 ` Jamie Lokier
2004-04-05 12:39 ` Jamie Lokier
2004-04-05 12:41 ` Jamie Lokier
2004-04-05 18:03 ` Jörn Engel
2004-04-05 11:10 ` jlnance
2004-04-05 11:46 ` Pavel Machek
2004-04-05 12:35 ` Jamie Lokier
2004-04-05 8:43 ` Jörn Engel
2004-04-03 19:47 ` Eric W. Biederman
2004-04-05 8:54 ` Jörn Engel
2004-04-05 9:07 ` Eric W. Biederman
2004-03-20 16:48 ` Davide Libenzi
2004-03-21 12:57 ` Jörn Engel
2004-03-21 17:59 ` Davide Libenzi
2004-03-21 18:14 ` Jörn Engel
2004-03-21 20:26 ` Davide Libenzi
2004-03-21 20:35 ` Jörn Engel
2004-03-22 0:18 ` Eric W. Biederman
2004-03-22 0:25 ` Davide Libenzi
2004-03-22 5:07 ` Eric W. Biederman
2004-03-22 5:11 ` Davide Libenzi
2004-03-22 11:20 ` Eric W. Biederman
2004-03-22 16:02 ` Davide Libenzi
2004-03-25 17:49 ` Jamie Lokier
2004-03-25 18:06 ` Eric W. Biederman
2004-03-25 19:43 ` Jamie Lokier
2004-03-25 20:38 ` Linus Torvalds
2004-03-25 22:16 ` Eric W. Biederman
2004-04-01 14:53 ` Jörn Engel
2004-04-02 11:54 ` Tim Connors
2004-03-25 21:46 ` Eric W. Biederman
2004-03-27 10:28 ` Jamie Lokier
2004-03-27 21:00 ` Eric W. Biederman
2004-03-27 21:42 ` Jamie Lokier
2004-03-27 23:45 ` Eric W. Biederman
2004-03-28 0:43 ` Eric W. Biederman
2004-03-28 12:22 ` Jamie Lokier
2004-03-28 20:07 ` Eric W. Biederman
2004-03-28 23:55 ` Jamie Lokier
2004-03-29 1:31 ` Eric W. Biederman
2004-03-29 12:36 ` Jamie Lokier
2004-03-29 19:36 ` Eric W. Biederman
2004-03-29 23:05 ` Jamie Lokier
2004-03-29 23:58 ` Eric W. Biederman
2004-03-29 7:45 ` Denis Vlasenko
2004-03-29 9:28 ` Pavel Machek
2004-03-29 12:40 ` Jamie Lokier
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