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

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Date:	Fri, 3 Apr 2009 02:22:09 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	david@...g.hm
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Theodore Tso <tytso@....edu>,
	Sitsofe Wheeler <sitsofe@...oo.com>,
	"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 Thu, Apr 02, 2009 at 06:17:12PM -0700, david@...g.hm wrote:
> On Fri, 3 Apr 2009, Matthew Garrett wrote:
> 
> >On Thu, Apr 02, 2009 at 05:59:53PM -0700, david@...g.hm wrote:
> >
> >>is laptop mode
> >>
> >>A. "write everything now, don't delay writes" in the hope that the drive
> >>will be idle enough later to spin down
> >
> >laptop-mode doesn't delay writes. Ever.
> >
> >>or
> >>
> >>B. "delay all writes until later, then when the drive wakes up do all
> >>pending writes at that time" so that the drive can go to sleep in the
> >>meantime?
> >
> >Yes.
> 
> you just contridicted yourself in these two statements.

That's because I'm horribly drunk and managed to confuse the order of 
your statements. My substantive point stands - the laptop-mode code 
doesn't delay writes, and it's pretty easy for anyone to prove this to 
themselves. Neither of your options actually describe its behaviour.
-- 
Matthew Garrett | mjg59@...f.ucam.org
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