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In contrast, the situation for > object cgroups has been different. > > Previously, the root object cgroup couldn't be returned because > it didn't exist. Now that a valid root object cgroup exists, for > the sake of consistency, it's necessary to align the behavior of > object-cgroup-related operations with that of memory cgroup APIs. > > Signed-off-by: Muchun Song > --- > include/linux/memcontrol.h | 29 ++++++++++++++++++------- > mm/memcontrol.c | 44 ++++++++++++++++++++------------------ > mm/percpu.c | 2 +- > 3 files changed, 45 insertions(+), 30 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index bb4f203733f3..e74922d5755d 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -319,6 +319,7 @@ struct mem_cgroup { > #define MEMCG_CHARGE_BATCH 64U > > extern struct mem_cgroup *root_mem_cgroup; > +extern struct obj_cgroup *root_obj_cgroup; > > enum page_memcg_data_flags { > /* page->memcg_data is a pointer to an slabobj_ext vector */ > @@ -528,6 +529,11 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) > return (memcg == root_mem_cgroup); > } > > +static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) > +{ > + return objcg == root_obj_cgroup; > +} > + > static inline bool mem_cgroup_disabled(void) > { > return !cgroup_subsys_enabled(memory_cgrp_subsys); > @@ -752,23 +758,26 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){ > > static inline bool obj_cgroup_tryget(struct obj_cgroup *objcg) > { > + if (obj_cgroup_is_root(objcg)) > + return true; > return percpu_ref_tryget(&objcg->refcnt); > } > > -static inline void obj_cgroup_get(struct obj_cgroup *objcg) > +static inline void obj_cgroup_get_many(struct obj_cgroup *objcg, > + unsigned long nr) > { > - percpu_ref_get(&objcg->refcnt); > + if (!obj_cgroup_is_root(objcg)) > + percpu_ref_get_many(&objcg->refcnt, nr); > } > > -static inline void obj_cgroup_get_many(struct obj_cgroup *objcg, > - unsigned long nr) > +static inline void obj_cgroup_get(struct obj_cgroup *objcg) > { > - percpu_ref_get_many(&objcg->refcnt, nr); > + obj_cgroup_get_many(objcg, 1); > } > > static inline void obj_cgroup_put(struct obj_cgroup *objcg) > { > - if (objcg) > + if (objcg && !obj_cgroup_is_root(objcg)) > percpu_ref_put(&objcg->refcnt); > } > > @@ -1101,6 +1110,11 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) > return true; > } > > +static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) > +{ > + return true; > +} > + > static inline bool mem_cgroup_disabled(void) > { > return true; > @@ -1684,8 +1698,7 @@ static inline struct obj_cgroup *get_obj_cgroup_from_current(void) > { > struct obj_cgroup *objcg = current_obj_cgroup(); > > - if (objcg) > - obj_cgroup_get(objcg); > + obj_cgroup_get(objcg); > > return objcg; > } > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a6362d11b46c..4aadc1b87db3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -81,6 +81,7 @@ struct cgroup_subsys memory_cgrp_subsys __read_mostly; > EXPORT_SYMBOL(memory_cgrp_subsys); > > struct mem_cgroup *root_mem_cgroup __read_mostly; > +struct obj_cgroup *root_obj_cgroup __read_mostly; > > /* Active memory cgroup to use from an interrupt context */ > DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg); > @@ -2525,15 +2526,14 @@ struct mem_cgroup *mem_cgroup_from_slab_obj(void *p) > > static struct obj_cgroup *__get_obj_cgroup_from_memcg(struct mem_cgroup *memcg) > { > - struct obj_cgroup *objcg = NULL; > + for (; memcg; memcg = parent_mem_cgroup(memcg)) { > + struct obj_cgroup *objcg = rcu_dereference(memcg->objcg); > > - for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) { > - objcg = rcu_dereference(memcg->objcg); > if (likely(objcg && obj_cgroup_tryget(objcg))) > - break; > - objcg = NULL; > + return objcg; > } > - return objcg; > + > + return NULL; > } > It appears that the return NULL statement might be dead code in this context. And would it be preferable to use return root_obj_cgroup instead? Best regards, Ridong > static struct obj_cgroup *current_objcg_update(void) > @@ -2604,18 +2604,17 @@ __always_inline struct obj_cgroup *current_obj_cgroup(void) > * Objcg reference is kept by the task, so it's safe > * to use the objcg by the current task. > */ > - return objcg; > + return objcg ? : root_obj_cgroup; > } > > memcg = this_cpu_read(int_active_memcg); > if (unlikely(memcg)) > goto from_memcg; > > - return NULL; > + return root_obj_cgroup; > > from_memcg: > - objcg = NULL; > - for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) { > + for (; memcg; memcg = parent_mem_cgroup(memcg)) { > /* > * Memcg pointer is protected by scope (see set_active_memcg()) > * and is pinning the corresponding objcg, so objcg can't go > @@ -2624,10 +2623,10 @@ __always_inline struct obj_cgroup *current_obj_cgroup(void) > */ > objcg = rcu_dereference_check(memcg->objcg, 1); > if (likely(objcg)) > - break; > + return objcg; > } > > - return objcg; > + return root_obj_cgroup; > } > > struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) > @@ -2641,14 +2640,8 @@ struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) > objcg = __folio_objcg(folio); > obj_cgroup_get(objcg); > } else { > - struct mem_cgroup *memcg; > - > rcu_read_lock(); > - memcg = __folio_memcg(folio); > - if (memcg) > - objcg = __get_obj_cgroup_from_memcg(memcg); > - else > - objcg = NULL; > + objcg = __get_obj_cgroup_from_memcg(__folio_memcg(folio)); > rcu_read_unlock(); > } > return objcg; > @@ -2733,7 +2726,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order) > int ret = 0; > > objcg = current_obj_cgroup(); > - if (objcg) { > + if (!obj_cgroup_is_root(objcg)) { > ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order); > if (!ret) { > obj_cgroup_get(objcg); > @@ -3036,7 +3029,7 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > * obj_cgroup_get() is used to get a permanent reference. > */ > objcg = current_obj_cgroup(); > - if (!objcg) > + if (obj_cgroup_is_root(objcg)) > return true; > > /* > @@ -3708,6 +3701,9 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > if (!objcg) > goto free_shrinker; > > + if (unlikely(mem_cgroup_is_root(memcg))) > + root_obj_cgroup = objcg; > + > objcg->memcg = memcg; > rcu_assign_pointer(memcg->objcg, objcg); > obj_cgroup_get(objcg); > @@ -5302,6 +5298,9 @@ void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size) > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > return; > > + if (obj_cgroup_is_root(objcg)) > + return; > + > VM_WARN_ON_ONCE(!(current->flags & PF_MEMALLOC)); > > /* PF_MEMALLOC context, charging must succeed */ > @@ -5329,6 +5328,9 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size) > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > return; > > + if (obj_cgroup_is_root(objcg)) > + return; > + > obj_cgroup_uncharge(objcg, size); > > rcu_read_lock(); > diff --git a/mm/percpu.c b/mm/percpu.c > index b35494c8ede2..3e54c6fca9bd 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -1616,7 +1616,7 @@ static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp, > return true; > > objcg = current_obj_cgroup(); > - if (!objcg) > + if (obj_cgroup_is_root(objcg)) > return true; > > if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size)))