Re: [PATCH] laptop mode

[Jens Axboe <axboe@suse.de>]

On Thu, Oct 09 2003, Jeff Garzik wrote:
> Jens Axboe wrote:
> >On Thu, Oct 09 2003, Marcelo Tosatti wrote:
> >
> >>
> >>On Thu, 9 Oct 2003, Jeff Garzik wrote:
> >>
> >>
> >>>Linux Kernel Mailing List wrote:
> >>>
> >>>>ChangeSet 1.1150.1.52, 2003/10/08 10:49:45-03:00, axboe@suse.de
> >>>>
> >>>>	[PATCH] laptop mode
> >>>>	
> >>>>	Hi Marcelo,
> >>>>	
> >>>>	Lots of people have been using this patch with great success, and 
> >>>>	it's
> >>>>	been in the SuSE kernel for some months now too. It is also in the 
> >>>>	-benh
> >>>>	ppc tree
> >>>>	
> >>>>	Basically, it introduces a write back mode of dirty and journal data
> >>>>	that is more suitable for laptops. At the block layer end, it 
> >>>>	schedules
> >>>>	write out of dirty data after the disk has been idle for 5 seconds.
> >>>>	
> >>>>	Laptop mode can be switched on and off with /proc/sys/vm/laptop_mode.
> >>>>	There is also a block_dump sysctl, which if enabled will dump who
> >>>>	dirties and writes out data. This is very helpful in pinning down 
> >>>>	who is
> >>>>	causing unnecessary writes to the disk.
> >>>
> >>>Red Hat just dropped this patch since it was suspected of data 
> >>>corruption ;-(
> >>
> >>Uh, oh... Jens? 
> >
> >
> >See my previous mail. I don't see any problems with it, and I've
> >certainly not heard of (or experienced myself) problems with the patch.
> >I'm waiting for Jeff to expand on his mail, surely he/RH must know more
> >about this issue.
> 
> 
> That's 100% of my knowledge.  Talk to arjan/davej/sct for more info...

CC'ed

> That's what RH's field testing showed us, ignore it if you wish... :)

As far as I can tell, laptop-mode cannot cause any corruption on it own
that cannot otherwise happen without laptop mode. So if you see
corruption, it is most likely exposing some other bug. Or the field
users run out of battery and 10 minutes of work goes down the drain,
that's a calcuated risk though.

-- 
Jens Axboe