On Fri, 2011-08-26 at 08:18 +0800, Wu Fengguang wrote: > On Thu, Aug 25, 2011 at 12:12:58AM +0800, Peter Zijlstra wrote: > > On Wed, 2011-08-24 at 08:12 +0800, Wu Fengguang wrote: > > > Put (6) into (4), we get > > > > > > balanced_rate_(i+1) = balanced_rate_(i) * 2 > > > = (write_bw / N) * 2 > > > > > > That means, any position imbalance will lead to balanced_rate > > > estimation errors if we follow (4). Whereas if (1)/(5) is used, we > > > always get the right balanced dirty ratelimit value whether or not > > > (pos_ratio == 1.0), hence make the rate estimation independent(*) of > > > dirty position control. > > > > > > (*) independent as in real values, not the seemingly relations in equation > > > > > > The assumption here is that N is a constant.. in the above case > > pos_ratio would eventually end up at 1 and things would be good again. I > > see your argument about oscillations, but I think you can introduce > > similar effects by varying N. > > Yeah, it's very possible for N to change over time, in which case > balanced_rate will adapt to new N in similar way. Gah.. but but but, that gives the same stuff as your (6)+(4). Why won't you accept that for pos_ratio but you don't mind for N ? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
