On Sun, 2009-08-23 at 15:27 +0800, Wu Fengguang wrote: > On Sun, Aug 23, 2009 at 01:31:17PM +0800, Peter Zijlstra wrote: > > On Sun, 2009-08-23 at 09:32 +0800, Wu Fengguang wrote: > > > > > I'd propose to remove the above 'if' and liberate the following three 'if's. > > > > > > > > That might work, but it looses the total dirty_thresh constraint. The > > > > sum of per-bdi dirties _should_ not be larger than that, but I'm not > > > > sure it won't ever be. > > > > > > > > The clip code Richard removed ensured that, and I think I wrote that out > > > > of more than sheer paranoia, but I'm not sure anymore :/ > > > > > > Oh I assumed that your per-bdi throttling is not too permissive to > > > exceed the global dirty_thresh. In theory the per-bdi throttling > > > should be able to quickly stop the growing of (nr_reclaimable + > > > nr_writeback). Once dirty_thresh is reached we already los > > > > Right, so: > > > > bdi_thresh_n = dirty_thresh * p(n) + eps. > > > > and > > > > \Sum_n p(n) = 1 > > > > So: > > > > \Sum_n bdi_thresh_n = dirty_thresh + n*eps > > > > Which yields an O(n) error bound. > > > > I'm just not sure how large the thing is in reality, and paranoia won > > out. > > A wild question: is it possible to make the equation: > > bdi_thresh_n = dirty_thresh * p(n) - eps. Possibly, I'd have to go over the math to get a proper equation for eps, then see what needs to be done to get avg(eps) <= 0. -- 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
