On Tue 24-01-12 09:18:21, Balbir Singh wrote: > On Tue, Jan 24, 2012 at 12:44 AM, Ying Han <yinghan@xxxxxxxxxx> wrote: > > On Mon, Jan 23, 2012 at 5:02 AM, Michal Hocko <mhocko@xxxxxxx> wrote: > >> On Sat 21-01-12 22:49:23, Hillf Danton wrote: > >>> In soft limit reclaim, overreclaim occurs when pages are reclaimed from mem > >>> group that is under its soft limit, or when more pages are reclaimd than the > >>> exceeding amount, then performance of reclaimee goes down accordingly. > >> > >> First of all soft reclaim is more a help for the global memory pressure > >> balancing rather than any guarantee about how much we reclaim for the > >> group. > >> We need to do more changes in order to make it a guarantee. > >> For example you implementation will cause severe problems when all > >> cgroups are soft unlimited (default conf.) or when nobody is above the > >> limit but the total consumption triggers the global reclaim. Therefore > >> nobody is in excess and you would skip all groups and only bang on the > >> root memcg. > >> > > True, ideally soft reclaim should not turn on and allow global reclaim > to occur in the scenario mentioned. > > >> Ying Han has a patch which basically skips all cgroups which are under > >> its limit until we reach a certain reclaim priority but even for this we > >> need some additional changes - e.g. reverse the current default setting > >> of the soft limit. > >> > > I'd be wary of that approach, because it might be harder to explain > the working of soft limits, This is an attempt to turn the soft reclaim into a "guarantee". Changing the default value from unlimited to 0 basically says that everybody will be considered under memory pressure unless the soft limit setting says otherwise. This btw. has been the case with the double (global and per-cgroup) LRUs as well. It was just hidden. > I'll look at the discussion thread mentioned earlier for the benefits > of that approach. > > >> Anyway, I like the nr_to_reclaim reduction idea because we have to do > >> this in some way because the global reclaim starts with ULONG > >> nr_to_scan. > > > > Agree with Michal where there are quite a lot changes we need to get > > in for soft limit before any further optimization. > > > > Hillf, please refer to the patch from Johannes > > https://lkml.org/lkml/2012/1/13/99 which got quite a lot recent > > discussions. I am expecting to get that in before further soft limit > > changes. > > Balbir > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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>