mm: memcontrol/slab: Use helpers to access slab page's memcg_data

To gather all direct accesses to struct page's memcg_data field in one
place, let's introduce 3 new helpers to use in the slab accounting code:

  struct obj_cgroup **page_objcgs(struct page *page);
  struct obj_cgroup **page_objcgs_check(struct page *page);
  bool set_page_objcgs(struct page *page, struct obj_cgroup **objcgs);

They are similar to the corresponding API for generic pages, except that
the setter can return false, indicating that the value has been already
set from a different thread.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20201027001657.3398190-3-guro@fb.com
Link: https://lore.kernel.org/bpf/20201201215900.3569844-3-guro@fb.com

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f95c143..c7ac0a5 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -416,6 +416,70 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
        return (struct mem_cgroup *)memcg_data;
 }
 
+#ifdef CONFIG_MEMCG_KMEM
+/*
+ * page_objcgs - get the object cgroups vector associated with a page
+ * @page: a pointer to the page struct
+ *
+ * Returns a pointer to the object cgroups vector associated with the page,
+ * or NULL. This function assumes that the page is known to have an
+ * associated object cgroups vector. It's not safe to call this function
+ * against pages, which might have an associated memory cgroup: e.g.
+ * kernel stack pages.
+ */
+static inline struct obj_cgroup **page_objcgs(struct page *page)
+{
+       return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL);
+}
+
+/*
+ * page_objcgs_check - get the object cgroups vector associated with a page
+ * @page: a pointer to the page struct
+ *
+ * Returns a pointer to the object cgroups vector associated with the page,
+ * or NULL. This function is safe to use if the page can be directly associated
+ * with a memory cgroup.
+ */
+static inline struct obj_cgroup **page_objcgs_check(struct page *page)
+{
+       unsigned long memcg_data = READ_ONCE(page->memcg_data);
+
+       if (memcg_data && (memcg_data & 0x1UL))
+               return (struct obj_cgroup **)(memcg_data & ~0x1UL);
+
+       return NULL;
+}
+
+/*
+ * set_page_objcgs - associate a page with a object cgroups vector
+ * @page: a pointer to the page struct
+ * @objcgs: a pointer to the object cgroups vector
+ *
+ * Atomically associates a page with a vector of object cgroups.
+ */
+static inline bool set_page_objcgs(struct page *page,
+                                       struct obj_cgroup **objcgs)
+{
+       return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL);
+}
+#else
+static inline struct obj_cgroup **page_objcgs(struct page *page)
+{
+       return NULL;
+}
+
+static inline struct obj_cgroup **page_objcgs_check(struct page *page)
+{
+       return NULL;
+}
+
+static inline bool set_page_objcgs(struct page *page,
+                                       struct obj_cgroup **objcgs)
+{
+       return true;
+}
+#endif
+
 static __always_inline bool memcg_stat_item_in_bytes(int idx)
 {
        if (idx == MEMCG_PERCPU_B)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3968d68..0054b48 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2899,7 +2899,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
        if (!vec)
                return -ENOMEM;
 
-       if (cmpxchg(&page->memcg_data, 0, (unsigned long)vec | 0x1UL))
+       if (!set_page_objcgs(page, vec))
                kfree(vec);
        else
                kmemleak_not_leak(vec);
@@ -2933,12 +2933,12 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
         * Memcg membership data for each individual object is saved in
         * the page->obj_cgroups.
         */
-       if (page_has_obj_cgroups(page)) {
+       if (page_objcgs_check(page)) {
                struct obj_cgroup *objcg;
                unsigned int off;
 
                off = obj_to_index(page->slab_cache, page, p);
-               objcg = page_obj_cgroups(page)[off];
+               objcg = page_objcgs(page)[off];
                if (objcg)
                        return obj_cgroup_memcg(objcg);
 

diff --git a/mm/slab.h b/mm/slab.h
index e2535ce..9a54a0c 100644 (file)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -239,28 +239,12 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
-{
-       /*
-        * Page's memory cgroup and obj_cgroups vector are sharing the same
-        * space. To distinguish between them in case we don't know for sure
-        * that the page is a slab page (e.g. page_cgroup_ino()), let's
-        * always set the lowest bit of obj_cgroups.
-        */
-       return (struct obj_cgroup **)(page->memcg_data & ~0x1UL);
-}
-
-static inline bool page_has_obj_cgroups(struct page *page)
-{
-       return page->memcg_data & 0x1UL;
-}
-
 int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
                                 gfp_t gfp);
 
 static inline void memcg_free_page_obj_cgroups(struct page *page)
 {
-       kfree(page_obj_cgroups(page));
+       kfree(page_objcgs(page));
        page->memcg_data = 0;
 }
 
@@ -322,7 +306,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
                if (likely(p[i])) {
                        page = virt_to_head_page(p[i]);
 
-                       if (!page_has_obj_cgroups(page) &&
+                       if (!page_objcgs(page) &&
                            memcg_alloc_page_obj_cgroups(page, s, flags)) {
                                obj_cgroup_uncharge(objcg, obj_full_size(s));
                                continue;
@@ -330,7 +314,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 
                        off = obj_to_index(s, page, p[i]);
                        obj_cgroup_get(objcg);
-                       page_obj_cgroups(page)[off] = objcg;
+                       page_objcgs(page)[off] = objcg;
                        mod_objcg_state(objcg, page_pgdat(page),
                                        cache_vmstat_idx(s), obj_full_size(s));
                } else {
@@ -344,6 +328,7 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
                                        void **p, int objects)
 {
        struct kmem_cache *s;
+       struct obj_cgroup **objcgs;
        struct obj_cgroup *objcg;
        struct page *page;
        unsigned int off;
@@ -357,7 +342,8 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
                        continue;
 
                page = virt_to_head_page(p[i]);
-               if (!page_has_obj_cgroups(page))
+               objcgs = page_objcgs(page);
+               if (!objcgs)
                        continue;
 
                if (!s_orig)
@@ -366,11 +352,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
                        s = s_orig;
 
                off = obj_to_index(s, page, p[i]);
-               objcg = page_obj_cgroups(page)[off];
+               objcg = objcgs[off];
                if (!objcg)
                        continue;
 
-               page_obj_cgroups(page)[off] = NULL;
+               objcgs[off] = NULL;
                obj_cgroup_uncharge(objcg, obj_full_size(s));
                mod_objcg_state(objcg, page_pgdat(page), cache_vmstat_idx(s),
                                -obj_full_size(s));
@@ -379,11 +365,6 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
 }
 
 #else /* CONFIG_MEMCG_KMEM */
-static inline bool page_has_obj_cgroups(struct page *page)
-{
-       return false;
-}
-
 static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
 {
        return NULL;