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

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Date:	Fri, 3 Apr 2009 02:19:53 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	david@...g.hm
Cc:	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 06:16:20PM -0700, david@...g.hm wrote:
> On Fri, 3 Apr 2009, Matthew Garrett wrote:
> 
> >On Thu, Apr 02, 2009 at 05:55:11PM -0700, david@...g.hm wrote:
> >>On Fri, 3 Apr 2009, Matthew Garrett wrote:
> >>>Then they shouldn't use a mail client that fsync()s.
> >>
> >>so they need to use one mail client when they want to have good battery
> >>life and a different one when they are plugged in to power?
> >
> >They need to make a decision about whether they care about their mailbox
> >being precisely in sync with their server or not, and either use a
> >client that adapts appropriately or choose a client that behaves
> >appropriately. It's certainly not the kernel's business.
> 
> the kernel is not deciding this, the kernel would be implementing the 
> user's choice

No it wouldn't. The kernel would be implementing an adminstrator's 
choice about whether fsync() is important or not. That's something that 
would affect the mail client, but it's hardly a decision based on the 
mail client. Sucks to be that user if they do anything involving mysql.

> >If you can demonstrate a real world use case where the hard drive
> >(typically well under a watt of power consumption on modern systems)
> >spindown policy will be affected sufficiently pathologically by a mail
> >client that you lose an hour of battery life, then I'd rethink this. But
> >mostly I'd conclude that this was an example of an inappropriate
> >spindown policy.
> 
> remember that the mail client was an example.
> 
> you want another example, think of anything that uses sqlite (like the 
> firefox history stuff, although that was weakened drasticly due to the 
> ext3 problems).

Benchmarks please.
-- 
Matthew Garrett | mjg59@...f.ucam.org
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