linux-kernel - Re: [rfc] Ignore Fsync Calls in Laptop

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Message-ID: <BANLkTimu2W4AXTGZsf-3QhO8YwgVMc6Riw@mail.gmail.com>
Date:	Tue, 31 May 2011 21:04:59 +0200
From:	"D. Jansen" <d.g.jansen@...glemail.com>
To:	david@...g.hm
Cc:	"Ted Ts'o" <tytso@....edu>, Oliver Neukum <oneukum@...e.de>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Dave Chinner <david@...morbit.com>, njs@...ox.com,
	bart@...wel.tk
Subject: Re: [rfc] Ignore Fsync Calls in Laptop_Mode

On Tue, May 31, 2011 at 8:54 PM,  <david@...g.hm> wrote:
> On Tue, 31 May 2011, D. Jansen wrote:
>
>> On Tue, May 31, 2011 at 8:23 PM,  <david@...g.hm> wrote:
>>>
>>> On Tue, 31 May 2011, D. Jansen wrote:
>>>
>>>> On Tue, May 31, 2011 at 4:03 AM, Ted Ts'o <tytso@....edu> wrote:
>>
>>>>> I can't remember the last time this has happened to me.  It's
>>>>> typically a system crash or a power loss that causes me to lose an
>>>>> OpenOffice session.
>>>>
>>>> Well, good for you! Power loss didn't ever occur to me on the other
>>>> hand, at least not on my netbook.
>>>
>>> failure to resume is effectivly power loss. a autosave to ram would be
>>> lost,
>>> just like with a power loss or system crash.
>>>
>> Well in my case only X crashes and the autosave is saved.
>
> but you have no guarantee that it would be saved without fsync.

But I would with barriers.
>
> it looks like libreoffice does 2 fsyncs per snapshot saved. This is why your
> data is saved.
>
> If this is only every 15 minutes (the default), and you have the disk
> spin-up time set to every 20 minutes, you will be spinning up the disk just
> about as frequently anyway.
>
> now if the system isn't flushing things to disk when it spins up for the
> fsync, then there is something wrong.
>
> but if it is working as designed, you get one spin-up every 15 min instead
> of one spin-up every 20 minutes, that should not be enough to kill anything.

Yes, if there was nothing else, that's probably true. But _many_
applications use fsync, even KDE's plasma shell I think.
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