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Depending on memory > pressure, page sharing patterns between different cgroups and cgroup > creation/destruction rates, many dying memory cgroups can be pinned > by pagecache pages, reducing page reclaim efficiency and wasting > memory. Converting LRU folios and most other raw memory cgroup pins > to the object cgroup direction can fix this long-living problem. > > As a result, the objcg infrastructure is no longer solely applicable > to the kmem case. In this patch, we extend the scope of the objcg > infrastructure beyond the kmem case, enabling LRU folios to reuse > it for folio charging purposes. > > It should be noted that LRU folios are not accounted for at the root > level, yet the folio->memcg_data points to the root_mem_cgroup. Hence, > the folio->memcg_data of LRU folios always points to a valid pointer. > However, the root_mem_cgroup does not possess an object cgroup. > Therefore, we also allocate an object cgroup for the root_mem_cgroup. > > Signed-off-by: Muchun Song > Signed-off-by: Qi Zheng > --- > mm/memcontrol.c | 51 +++++++++++++++++++++++-------------------------- > 1 file changed, 24 insertions(+), 27 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d5257465c9d75..2afd7f99ca101 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -204,10 +204,10 @@ static struct obj_cgroup *obj_cgroup_alloc(void) > return objcg; > } > > -static void memcg_reparent_objcgs(struct mem_cgroup *memcg, > - struct mem_cgroup *parent) > +static void memcg_reparent_objcgs(struct mem_cgroup *memcg) > { > struct obj_cgroup *objcg, *iter; > + struct mem_cgroup *parent = parent_mem_cgroup(memcg); > > objcg = rcu_replace_pointer(memcg->objcg, NULL, true); > > @@ -3302,30 +3302,17 @@ unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) > return val; > } > > -static int memcg_online_kmem(struct mem_cgroup *memcg) > +static void memcg_online_kmem(struct mem_cgroup *memcg) > { > - struct obj_cgroup *objcg; > - > if (mem_cgroup_kmem_disabled()) > - return 0; > + return; > > if (unlikely(mem_cgroup_is_root(memcg))) > - return 0; > - > - objcg = obj_cgroup_alloc(); > - if (!objcg) > - return -ENOMEM; > - > - objcg->memcg = memcg; > - rcu_assign_pointer(memcg->objcg, objcg); > - obj_cgroup_get(objcg); > - memcg->orig_objcg = objcg; > + return; > > static_branch_enable(&memcg_kmem_online_key); > > memcg->kmemcg_id = memcg->id.id; > - > - return 0; > } > > static void memcg_offline_kmem(struct mem_cgroup *memcg) > @@ -3340,12 +3327,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) > > parent = parent_mem_cgroup(memcg); > memcg_reparent_list_lrus(memcg, parent); > - > - /* > - * Objcg's reparenting must be after list_lru's, make sure list_lru > - * helpers won't use parent's list_lru until child is drained. > - */ > - memcg_reparent_objcgs(memcg, parent); > } > > #ifdef CONFIG_CGROUP_WRITEBACK > @@ -3862,9 +3843,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) > static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > { > struct mem_cgroup *memcg = mem_cgroup_from_css(css); > + struct obj_cgroup *objcg; > > - if (memcg_online_kmem(memcg)) > - goto remove_id; > + memcg_online_kmem(memcg); > > /* > * A memcg must be visible for expand_shrinker_info() > @@ -3874,6 +3855,15 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > if (alloc_shrinker_info(memcg)) > goto offline_kmem; > > + objcg = obj_cgroup_alloc(); > + if (!objcg) > + goto free_shrinker; > + > + objcg->memcg = memcg; > + rcu_assign_pointer(memcg->objcg, objcg); > + obj_cgroup_get(objcg); > + memcg->orig_objcg = objcg; > + Will it be better to add a helper function like obj_cgroup_init()? > if (unlikely(mem_cgroup_is_root(memcg)) && !mem_cgroup_disabled()) > queue_delayed_work(system_unbound_wq, &stats_flush_dwork, > FLUSH_TIME); > @@ -3896,9 +3886,10 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > xa_store(&mem_cgroup_ids, memcg->id.id, memcg, GFP_KERNEL); > > return 0; > +free_shrinker: > + free_shrinker_info(memcg); > offline_kmem: > memcg_offline_kmem(memcg); > -remove_id: > mem_cgroup_id_remove(memcg); > return -ENOMEM; > } > @@ -3916,6 +3907,12 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) > > memcg_offline_kmem(memcg); > reparent_deferred_split_queue(memcg); > + /* > + * The reparenting of objcg must be after the reparenting of the > + * list_lru and deferred_split_queue above, which ensures that they will > + * not mistakenly get the parent list_lru and deferred_split_queue. > + */ > + memcg_reparent_objcgs(memcg); > reparent_shrinker_deferred(memcg); > wb_memcg_offline(memcg); > lru_gen_offline_memcg(memcg); -- Best regards, Ridong