Re: Ext4 and the "30 second window of death"

[david]

On Fri, 3 Apr 2009, Matthew Garrett wrote:

> On Thu, Apr 02, 2009 at 05:59:53PM -0700, david@xxxxxxx 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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