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)
