Re: Increase dirty_ratio and dirty_background_ratio?

Linus Torvalds
2009-01-08T17:05:34Z

On Thu, 8 Jan 2009, Chris Mason wrote:
>
> Does it make sense to hook into kupdate? If kupdate finds it can't meet
> the no-data-older-than 30 seconds target, it lowers the sync/async combo
> down to some reasonable bottom.
>
> If it finds it is going to sleep without missing the target, raise the
> combo up to some reasonable top.

I like autotuning, so that sounds like an intriguing approach. It's worked
for us before (ie VM).

That said, 30 seconds sounds like a _loong_ time for something like this.
I'd use the normal 5-second dirty_writeback_interval for this: if we can't
clean the whole queue in that normal background writeback interval, then
we try to lower the tagets. We already have that "congestion_wait()" thing
there, that would be a logical place, methinks.

I'm not sure how to raise them, though. We don't want to raise any limits
just because the user suddenly went idle. I think the raising should
happen if we hit the sync/async ratio, and we haven't lowered in the last
30 seconds or something like that.

Linus