Comment 273 for bug 620074

(In reply to comment #259)
> I've been doing some testing - two tunables I've found (briefly mentioned
> earlier) that helps immensely is setting /proc/sys/vm/dirty_background_ratio
> to
> 1 and /proc/sys/vm/dirty_ratio to 2.
>
> On some of my systems that I've run the test on it reduces latency down to a
> fraction of a second - on other systems it reduces it from 20+ seconds to
> less
> than 10.
>
> Anyone else see similar behaviour with my simple test?
>

This is right. Although it doesn't eliminate stutter (mouse freezing for 1-2 seconds) during heavy IO, it does make that stutter tolerable. Its basically converting your IO to almost sync inline instead of leaving the work for later for pdflush to pick up and choke the hell out of the IO subsystem. I have no idea why on larger memory configurations those default values are set so high as 40 and 20 (IIRC). I mean on a 4GB RAM system, we may not see any IO landing until expiry alarms fire in pdflush or 40% of 4GB=1.6G is ready to be written.