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SubjectRe: [rfc] Ignore Fsync Calls in Laptop_Mode
On Tue, May 31, 2011 at 4:03 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Mon, May 30, 2011 at 11:24:03PM +0200, D. Jansen wrote:
>> > do you really have so many fsync's going on that the disk spins up so much
>> > that you would gain 10-20% battery life?
>>
>> Yes. Every autosave in LibreOffice triggers one. And I want autosave,
>> but I want them in memory, not on disk.
>
> What on *heck* good does an autosave to memory do?  Are you afraid
> your X server is going to go poof, or OpenOffice is going to crash on
> you?
Unfortunately, yes. This happens to me regularly, e.g. roughly every
10th resume. It's a poulsbo system. ;)
Another reason is a Java extension that makes it crash happy.
(Please don't tell me now that the real fix is to fix poulsbo...)

>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.

>> > and what makes you think the extra spin-ups from fsyncs will cause your hard
>> > drive to fail significantly earlier? (if you have a hard drive with a
>> > limited number of spin-up cycles, you probably don't want to use laptop mode
>> > at all)
>>
>> Experience, see above. Also, this is well described behavior. All hard
>> disks are only designed to last a certain number of head loads and
>> unloads. Spinning up and down even less.
>
> Modern laptop drives are designed for 600,000 to a million head loads
> and unloads.  Open Office by default autosaves once every 15 minutes.
> So if you leave your system running (on battery?!?) 24x7, with open
> office open all that time, even with HDD which is only rated for 600k
> load cycles, that's 4.5 years.

Yeah, exactly what I had thought -- enabling laptop mode for the first time.
After the hard disk started to show more read errors
and almost crashed so I had to exchange it, I reconsidered.
I wish specifications would be more in conformity with reality...
Good thing I watch my smart log and caught it in time to avoid data loss.
Though I do have a solid backup routine to avoid serious issues.

> And of course, normally such a system
> is powered all the time, and the hard drive shouldn't be spinning down
> if you're on the AC mains.

Well, I use my netbook on the go mostly. I guess we just have different habits.
>
> The real fix is that applications need to be fixed to be less
> write-happy.  Firefox example, used to request a transactional update
> to a sqllite database on every web click.  Laptop mode isn't the right
> place to fix this, since if you try to stop the writes from hitting
> the disk, you'll still end up burning memory that can't be released
> until the data is written to disk. (...)

That is another fix that everybody can benefit from. And another
reason to provide barrier support for user space.
(We have a new trojan horse!)
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