linux-kernel - Re: Ext4 and the "30 second window of death"

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Date:	Wed, 1 Apr 2009 06:20:50 +0100
From:	Sitsofe Wheeler <sitsofe@...oo.com>
To:	Theodore Tso <tytso@....edu>,
	"Andreas T.Auer" <andreas.t.auer_lkml_73537@...us.ath.cx>,
	Alberto Gonzalez <info@...bu.es>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Ext4 and the "30 second window of death"

On Tue, Mar 31, 2009 at 09:50:10PM -0400, Theodore Tso wrote:
> 
> But still, you're right.  In some cases, you really want "fsync()" to
> mean "fsync()".  I'm not sure how often such applications _should_ be

Hmm. This is starting to sound a lot like the OSX fsync (
http://developer.apple.com/documentation/Darwin/Reference/Manpages/man2/fsync.2.html
) where there is effectively a "fsync harder" syscall
(F_FULLFSYNC fcntl11).

> If all they are doing is browsing the web, and the issue is firefox's
> desire to constantly write to their home directory, the user should be
> able to say, "you know, my battery life is more important that making
> sure that every last web page I visit is saved away in some file ---
> Firefox's 'Awesome Bar' really isn't worth that much to me."

The "Awesome(bar) Firefox 3 fsync Problem" isn't that you are missing a
day's worth of browsing. The issue is that the sqlite database might
become corrupt and lose _all history_ if fsync lies/doesn't happen and a
crash occurs ( https://bugzilla.mozilla.org/show_bug.cgi?id=435712#c10).
With Firefox 2 there was a file swap happening so an fsync wasn't vital.

Just out of curiosity, when laptop mode is happening is there a
guarantee that writes to other files won't be reordered to before the
fsync? 

-- 
Sitsofe | http://sucs.org/~sits/
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