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

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Date:	Thu, 2 Apr 2009 18:17:12 -0700 (PDT)
From:	david@...g.hm
To:	Matthew Garrett <mjg59@...f.ucam.org>
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 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.

David Lang

>> I've heard things in these threads that would indicate both behaviors.
>
> The code's pretty trivial. The only real functional differences
> laptop-mode brings are to write out all dirty pages (rather than just
> writing down to the watermark) and to call sys_sync() a few seconds
> after the last thing that hit disk rather than being satisfied from
> cache. It's entirely a mechanism to opportunistically take advantage of
> the disk being spun up.
>
>
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