Messages in this thread | | | Date | Tue, 2 Mar 2021 10:58:36 -0800 | From | Roman Gushchin <> | Subject | Re: [PATCH] mm: memcontrol: fix root_mem_cgroup charging |
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On Tue, Mar 02, 2021 at 04:18:23PM +0800, Muchun Song wrote: > CPU0: CPU1: > > objcg = get_obj_cgroup_from_current(); > obj_cgroup_charge(objcg); > memcg_reparent_objcgs(); > xchg(&objcg->memcg, root_mem_cgroup); > // memcg == root_mem_cgroup > memcg = obj_cgroup_memcg(objcg); > __memcg_kmem_charge(memcg); > // Do not charge to the root memcg > try_charge(memcg); > > If the objcg->memcg is reparented to the root_mem_cgroup, > obj_cgroup_charge() can pass root_mem_cgroup as the first > parameter to here. The root_mem_cgroup is skipped in the > try_charge(). So the page counters of it do not update. > > When we uncharge this, we will decrease the page counters > (e.g. memory and memsw) of the root_mem_cgroup. This will > cause the page counters of the root_mem_cgroup to be out > of balance. Fix it by charging the page to the > root_mem_cgroup unconditional.
Is this a problem? It seems that we do not expose root memcg's counters except kmem and tcp. It seems that the described problem is not applicable to the kmem counter. Please, explain.
Thanks!
> > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > --- > mm/memcontrol.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 2db2aeac8a9e..edf604824d63 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3078,6 +3078,19 @@ static int __memcg_kmem_charge(struct mem_cgroup *memcg, gfp_t gfp, > if (ret) > return ret; > > + /* > + * If the objcg->memcg is reparented to the root_mem_cgroup, > + * obj_cgroup_charge() can pass root_mem_cgroup as the first > + * parameter to here. We should charge the page to the > + * root_mem_cgroup unconditional to keep it's page counters > + * balance. > + */ > + if (unlikely(mem_cgroup_is_root(memcg))) { > + page_counter_charge(&memcg->memory, nr_pages); > + if (do_memsw_account()) > + page_counter_charge(&memcg->memsw, nr_pages); > + } > + > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && > !page_counter_try_charge(&memcg->kmem, nr_pages, &counter)) { > > -- > 2.11.0 >
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