On Sat 23-07-11 15:43:45, Wu Fengguang wrote: > On Fri, Jul 15, 2011 at 05:34:09AM +0800, Jan Kara wrote: > > > - tasks dirtying close to 25% pages probably cannot be called light > > > dirtier and there is no need to protect such tasks > > The idea is interesting. The only problem is that we don't want to set > > dirty_exceeded too late so that heavy dirtiers won't push light dirtiers > > over their limits so easily due to ratelimiting. It did some computations: > > We normally ratelimit after 4 MB. Take a low end desktop these days. Say > > 1 GB of ram, 4 CPUs. So dirty limit will be ~200 MB and the area for task > > differentiation ~25 MB. We enter balance_dirty_pages() after dirtying > > num_cpu * ratelimit / 2 pages on average which gives 8 MB. So we should > > set dirty_exceeded at latest at bdi_dirty / TASK_LIMIT_FRACTION / 2 or > > task differentiation would have no effect because of ratelimiting. > > > > So we could change the limit to something like: > > bdi_dirty - min(bdi_dirty / TASK_LIMIT_FRACTION, ratelimit_pages * > > num_online_cpus / 2 + bdi_dirty / TASK_LIMIT_FRACTION / 16) > > Good analyze! > > > But I'm not sure setups where this would make difference are common... > > I think I'd prefer the original simple patch given that the common > 1-dirtier is not impacted. OK, thanks. So will you merge the patch please? Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>