On Fri 27-01-23 05:12:13, Leonardo Brás wrote: > On Fri, 2023-01-27 at 04:22 -0300, Leonardo Brás wrote: > > On Fri, 2023-01-27 at 08:11 +0100, Michal Hocko wrote: > > > [Cc Frederic] > > > > > > On Thu 26-01-23 15:12:35, Roman Gushchin wrote: > > > > On Thu, Jan 26, 2023 at 08:41:34AM +0100, Michal Hocko wrote: > > > [...] > > > > > > Essentially each cpu will try to grab the remains of the memory quota > > > > > > and move it locally. I wonder in such circumstances if we need to disable the pcp-caching > > > > > > on per-cgroup basis. > > > > > > > > > > I think it would be more than sufficient to disable pcp charging on an > > > > > isolated cpu. > > > > > > > > It might have significant performance consequences. > > > > > > Is it really significant? > > > > > > > I'd rather opt out of stock draining for isolated cpus: it might slightly reduce > > > > the accuracy of memory limits and slightly increase the memory footprint (all > > > > those dying memcgs...), but the impact will be limited. Actually it is limited > > > > by the number of cpus. > > > > > > Hmm, OK, I have misunderstood your proposal. Yes, the overal pcp charges > > > potentially left behind should be small and that shouldn't really be a > > > concern for memcg oom situations (unless the limit is very small and > > > workloads on isolated cpus using small hard limits is way beyond my > > > imagination). > > > > > > My first thought was that those charges could be left behind without any > > > upper bound but in reality sooner or later something should be running > > > on those cpus and if the memcg is gone the pcp cache would get refilled > > > and old charges gone. > > > > > > So yes, this is actually a better and even simpler solution. All we need > > > is something like this > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > index ab457f0394ab..13b84bbd70ba 100644 > > > --- a/mm/memcontrol.c > > > +++ b/mm/memcontrol.c > > > @@ -2344,6 +2344,9 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > > > struct mem_cgroup *memcg; > > > bool flush = false; > > > > > > + if (cpu_is_isolated(cpu)) > > > + continue; > > > + > > > rcu_read_lock(); > > > memcg = stock->cached; > > > if (memcg && stock->nr_pages && > > > > > > There is no such cpu_is_isolated() AFAICS so we would need a help from > > > NOHZ and cpuisol people to create one for us. Frederic, would such an > > > abstraction make any sense from your POV? > > > > > > IIUC, 'if (cpu_is_isolated())' would be instead: > > > > if (!housekeeping_cpu(smp_processor_id(), HK_TYPE_DOMAIN) || > > !housekeeping_cpu(smp_processor_id(), HK_TYPE_WQ) > > oh, sorry 's/smp_processor_id()/cpu/' here: > > if(!housekeeping_cpu(cpu, HK_TYPE_DOMAIN) || !housekeeping_cpu(cpu, HK_TYPE_WQ)) Or maybe we can get a nice abstract API so that we do not have to really care about those low level details. I do not really know what those really mean and hopefully I shouldn't really need to know. -- Michal Hocko SUSE Labs
