Re: Maximum reasonable bgwriter_delay

On Tue, 19 Jun 2007, Heikki Linnakangas wrote:

> Simon Riggs wrote:
>> Laptop mode? Linux has it...
>
> Granted, though you're still going to wake up every second, so I'm not sure
> how much it helps with battery life.

In this context, Linux's laptop mode is all about keeping the disks from
spinning up any more than they have to; the fact that the CPU does a
little something occasionally isn't so important. I don't think that's an
argument for keeping the current range for this parameter though. The
goal for a proper laptop mode tuning is for the hard drive to go minutes
at a time between waking, and whether bgwriter_delay is 1s or 10s really
isn't that big of a difference relative to that scale. Unless you dirty a
lot of memory, the laptop mode tuning is going to cache all the writes
anyway until it hits the interval where it wakes the disk to catch up.

I can't think of any good reason why the bgwriter_delay can't be reduced
to 1s if that simplifies things. You'd need a pretty old system for a
longer delay than that to be appropriate.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD