On Mon, Mar 14, 2011 at 2:10 PM, Jan Kara <jack@xxxxxxx> wrote: > On Mon 14-03-11 13:54:08, Vivek Goyal wrote: >> On Fri, Mar 11, 2011 at 10:43:30AM -0800, Greg Thelen wrote: >> > If the current process is in a non-root memcg, then >> > balance_dirty_pages() will consider the memcg dirty limits as well as >> > the system-wide limits. This allows different cgroups to have distinct >> > dirty limits which trigger direct and background writeback at different >> > levels. >> > >> > If called with a mem_cgroup, then throttle_vm_writeout() queries the >> > given cgroup for its dirty memory usage limits. >> > >> > Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx> >> > Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> >> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> >> > Acked-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> >> > --- >> > Changelog since v5: >> > - Simplified this change by using mem_cgroup_balance_dirty_pages() rather than >> > cramming the somewhat different logic into balance_dirty_pages(). This means >> > the global (non-memcg) dirty limits are not passed around in the >> > struct dirty_info, so there's less change to existing code. >> >> Yes there is less change to existing code but now we also have a separate >> throttlig logic for cgroups. >> >> I thought that we are moving in the direction of IO less throttling >> where bdi threads always do the IO and Jan Kara also implemented the >> logic to distribute the finished IO pages uniformly across the waiting >> threads. > Yes, we'd like to avoid doing IO from balance_dirty_pages(). But if the > logic in cgroups specific part won't get too fancy (which it doesn't seem > to be the case currently), it shouldn't be too hard to convert it to the new > approach. Handling memcg hierarchy was something that was not trivial to implement in mem_cgroup_balance_dirty_pages. > We can talk about it at LSF but at least with my approach to IO-less > balance_dirty_pages() it would be easy to convert cgroups throttling to > the new way. With Fengguang's approach it might be a bit harder since he > computes a throughput and from that necessary delay for a throttled task > but with cgroups that is impossible to compute so he'd have to add some > looping if we didn't write enough pages from the cgroup yet. But still it > would be reasonable doable AFAICT. I am definitely interested in finding a way to merge these feature cleanly together. >> Keeping it separate for cgroups, reduces the complexity but also forks >> off the balancing logic for root and other cgroups. So if Jan Kara's >> changes go in, it automatically does not get used for memory cgroups. >> >> Not sure how good a idea it is to use a separate throttling logic for >> for non-root cgroups. > Yeah, it looks a bit odd. I'd think that we could just cap > task_dirty_limit() by a value computed from a cgroup limit and be done > with that but I probably miss something... That is an interesting idea. When looking at upstream balance_dirty_pages(), the result of task_dirty_limit() is compared per bdi_nr_reclaimable and bdi_nr_writeback. I think we should be comparing memcg usage to memcg limits to catch cases where memcg usage is above memcg limits. Or am I missing something in your apporach? > Sure there is also a different > background limit but that's broken anyway because a flusher thread will > quickly stop doing writeback if global background limit is not exceeded. > But that's a separate topic so I'll reply with this to a more appropriate > email ;) ;) I am also interested in the this bg issue, but I should also try to stay on topic. > Honza > -- > Jan Kara <jack@xxxxxxx> > SUSE Labs, CR > -- 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
