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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695827341; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jeQJ/eIJXU0AYA9yk+s4aO7OKAgQk2qdJmGkoMOLMDk=; b=c6ZuccPLxLC+Ce4wWZ9aCvoGVbip0UFScbqDK/VCUHTzImAhP4V7Ea1dW8CIa6yy8rjLZJ 0Sp2j/SlVWnSus6gz0MlC0eiKozxqUtiaYSQ8bVhbIgA/srrcTqQNsoM1ecUX491WcPVhw WEyQ3zRkmTvotbuHgAt2bGqQFn9TnMI= From: Roman Gushchin To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , Dennis Zhou , Andrew Morton , Roman Gushchin Subject: [PATCH rfc 4/5] mm: kmem: scoped objcg protection Date: Wed, 27 Sep 2023 08:08:31 -0700 Message-ID: <20230927150832.335132-5-roman.gushchin@linux.dev> In-Reply-To: <20230927150832.335132-1-roman.gushchin@linux.dev> References: <20230927150832.335132-1-roman.gushchin@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 5918720022 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: ysc9oo5tgchq18e91ug87a3mpdi5tc4a X-HE-Tag: 1695827343-783950 X-HE-Meta: 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 gAduND7Z ySCSpmLYCTV5fAYhBuMNvn+8OoAX8RkSU9nLgEB0UQIG9tuIF6ZKG1Nn9BvpZFwIDZZDvxqAucZAN4sI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Switch to a scope-based protection of the objcg pointer on slab/kmem allocation paths. Instead of using the get_() semantics in the pre-allocation hook and put the reference afterwards, let's rely on the fact that objcg is pinned by the scope. It's possible because: 1) if the objcg is received from the current task struct, the task is keeping a reference to the objcg. 2) if the objcg is received from an active memcg (remote charging), the memcg is pinned by the scope and has a reference to the corresponding objcg. Signed-off-by: Roman Gushchin (Cruise) --- include/linux/memcontrol.h | 6 +++++ mm/memcontrol.c | 46 ++++++++++++++++++++++++++++++++++++-- mm/slab.h | 10 +++------ 3 files changed, 53 insertions(+), 9 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 412ff0e8694d..9a5212d3b9d8 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1779,6 +1779,12 @@ bool mem_cgroup_kmem_disabled(void); int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order); void __memcg_kmem_uncharge_page(struct page *page, int order); +/* + * The returned objcg pointer is safe to use without additional + * protection within a scope, refer to the implementation for the + * additional details. + */ +struct obj_cgroup *current_obj_cgroup(void); struct obj_cgroup *get_obj_cgroup_from_current(void); struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4815f897758c..76557370f212 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3074,6 +3074,48 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) return objcg; } +__always_inline struct obj_cgroup *current_obj_cgroup(void) +{ + struct mem_cgroup *memcg; + struct obj_cgroup *objcg; + + if (in_task()) { + memcg = current->active_memcg; + if (unlikely(memcg)) + goto from_memcg; + + objcg = READ_ONCE(current->objcg); + if (unlikely(current_objcg_needs_update(objcg))) + objcg = current_objcg_update(objcg); + /* + * Objcg reference is kept by the task, so it's safe + * to use the objcg by the current task. + */ + return objcg; + } else { + memcg = this_cpu_read(int_active_memcg); + if (unlikely(memcg)) + goto from_memcg; + } + return NULL; + +from_memcg: + for (; !mem_cgroup_is_root(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 + * away and can be used within the scope without any additional + * protection. + */ + objcg = rcu_dereference_check(memcg->objcg, 1); + if (likely(objcg)) + break; + objcg = NULL; + } + + return objcg; +} + struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) { struct obj_cgroup *objcg; @@ -3168,15 +3210,15 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order) struct obj_cgroup *objcg; int ret = 0; - objcg = get_obj_cgroup_from_current(); + objcg = current_obj_cgroup(); if (objcg) { ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order); if (!ret) { + obj_cgroup_get(objcg); page->memcg_data = (unsigned long)objcg | MEMCG_DATA_KMEM; return 0; } - obj_cgroup_put(objcg); } return ret; } diff --git a/mm/slab.h b/mm/slab.h index 799a315695c6..8cd3294fedf5 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -484,7 +484,7 @@ static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s, if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT)) return true; - objcg = get_obj_cgroup_from_current(); + objcg = current_obj_cgroup(); if (!objcg) return true; @@ -497,17 +497,14 @@ static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s, css_put(&memcg->css); if (ret) - goto out; + return false; } if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) - goto out; + return false; *objcgp = objcg; return true; -out: - obj_cgroup_put(objcg); - return false; } static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, @@ -542,7 +539,6 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, obj_cgroup_uncharge(objcg, obj_full_size(s)); } } - obj_cgroup_put(objcg); } static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,