mm/memcg: Convert slab objcgs from struct page to struct slab

page->memcg_data is used with MEMCG_DATA_OBJCGS flag only for slab pages
so convert all the related infrastructure to struct slab. Also use
struct folio instead of struct page when resolving object pointers.

This is not just mechanistic changing of types and names. Now in
mem_cgroup_from_obj() we use folio_test_slab() to decide if we interpret
the folio as a real slab instead of a large kmalloc, instead of relying
on MEMCG_DATA_OBJCGS bit that used to be checked in page_objcgs_check().
Similarly in memcg_slab_free_hook() where we can encounter
kmalloc_large() pages (here the folio slab flag check is implied by
virt_to_slab()). As a result, page_objcgs_check() can be dropped instead
of converted.

To avoid include cycles, move the inline definition of slab_objcgs()
from memcontrol.h to mm/slab.h.

Signed-off-by: Vlastimil Babka <[email protected]>
Reviewed-by: Roman Gushchin <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: <[email protected]>

Author: tehcaster

include/linux/memcontrol.h

@@ -536,61 +536,13 @@ static inline bool folio_memcg_kmem(struct folio *folio)
 	return folio->memcg_data & MEMCG_DATA_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)
-{
-	unsigned long memcg_data = READ_ONCE(page->memcg_data);
-
-	VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page);
-	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page);
-
-	return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
-}
-
-/*
- * 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 & MEMCG_DATA_OBJCGS))
-		return NULL;
-
-	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page);
-
-	return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
-}
 
 #else
 static inline bool folio_memcg_kmem(struct folio *folio)
 {
 	return false;
 }
 
-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;
-}
 #endif
 
 static inline bool PageMemcgKmem(struct page *page)

mm/memcontrol.c

@@ -2816,31 +2816,31 @@ static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
 	rcu_read_unlock();
 }
 
-int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
-				 gfp_t gfp, bool new_page)
+int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
+				 gfp_t gfp, bool new_slab)
 {
-	unsigned int objects = objs_per_slab(s, page_slab(page));
+	unsigned int objects = objs_per_slab(s, slab);
 	unsigned long memcg_data;
 	void *vec;
 
 	gfp &= ~OBJCGS_CLEAR_MASK;
 	vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp,
-			   page_to_nid(page));
+			   slab_nid(slab));
 	if (!vec)
 		return -ENOMEM;
 
 	memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS;
-	if (new_page) {
+	if (new_slab) {
 		/*
-		 * If the slab page is brand new and nobody can yet access
-		 * it's memcg_data, no synchronization is required and
-		 * memcg_data can be simply assigned.
+		 * If the slab is brand new and nobody can yet access its
+		 * memcg_data, no synchronization is required and memcg_data can
+		 * be simply assigned.
 		 */
-		page->memcg_data = memcg_data;
-	} else if (cmpxchg(&page->memcg_data, 0, memcg_data)) {
+		slab->memcg_data = memcg_data;
+	} else if (cmpxchg(&slab->memcg_data, 0, memcg_data)) {
 		/*
-		 * If the slab page is already in use, somebody can allocate
-		 * and assign obj_cgroups in parallel. In this case the existing
+		 * If the slab is already in use, somebody can allocate and
+		 * assign obj_cgroups in parallel. In this case the existing
 		 * objcg vector should be reused.
 		 */
 		kfree(vec);
@@ -2865,38 +2865,43 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
  */
 struct mem_cgroup *mem_cgroup_from_obj(void *p)
 {
-	struct page *page;
+	struct folio *folio;
 
 	if (mem_cgroup_disabled())
 		return NULL;
 
-	page = virt_to_head_page(p);
+	folio = virt_to_folio(p);
 
 	/*
 	 * Slab objects are accounted individually, not per-page.
 	 * Memcg membership data for each individual object is saved in
-	 * the page->obj_cgroups.
+	 * slab->memcg_data.
 	 */
-	if (page_objcgs_check(page)) {
-		struct obj_cgroup *objcg;
+	if (folio_test_slab(folio)) {
+		struct obj_cgroup **objcgs;
+		struct slab *slab;
 		unsigned int off;
 
-		off = obj_to_index(page->slab_cache, page_slab(page), p);
-		objcg = page_objcgs(page)[off];
-		if (objcg)
-			return obj_cgroup_memcg(objcg);
+		slab = folio_slab(folio);
+		objcgs = slab_objcgs(slab);
+		if (!objcgs)
+			return NULL;
+
+		off = obj_to_index(slab->slab_cache, slab, p);
+		if (objcgs[off])
+			return obj_cgroup_memcg(objcgs[off]);
 
 		return NULL;
 	}
 
 	/*
-	 * page_memcg_check() is used here, because page_has_obj_cgroups()
-	 * check above could fail because the object cgroups vector wasn't set
-	 * at that moment, but it can be set concurrently.
+	 * page_memcg_check() is used here, because in theory we can encounter
+	 * a folio where the slab flag has been cleared already, but
+	 * slab->memcg_data has not been freed yet
 	 * page_memcg_check(page) will guarantee that a proper memory
 	 * cgroup pointer or NULL will be returned.
 	 */
-	return page_memcg_check(page);
+	return page_memcg_check(folio_page(folio, 0));
 }
 
 __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)

mm/slab.h

@@ -412,15 +412,33 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
-				 gfp_t gfp, bool new_page);
+/*
+ * slab_objcgs - get the object cgroups vector associated with a slab
+ * @slab: a pointer to the slab struct
+ *
+ * Returns a pointer to the object cgroups vector associated with the slab,
+ * or NULL if no such vector has been associated yet.
+ */
+static inline struct obj_cgroup **slab_objcgs(struct slab *slab)
+{
+	unsigned long memcg_data = READ_ONCE(slab->memcg_data);
+
+	VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS),
+							slab_page(slab));
+	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, slab_page(slab));
+
+	return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+}
+
+int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
+				 gfp_t gfp, bool new_slab);
 void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 		     enum node_stat_item idx, int nr);
 
-static inline void memcg_free_page_obj_cgroups(struct page *page)
+static inline void memcg_free_slab_cgroups(struct slab *slab)
 {
-	kfree(page_objcgs(page));
-	page->memcg_data = 0;
+	kfree(slab_objcgs(slab));
+	slab->memcg_data = 0;
 }
 
 static inline size_t obj_full_size(struct kmem_cache *s)
@@ -465,7 +483,7 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 					      gfp_t flags, size_t size,
 					      void **p)
 {
-	struct page *page;
+	struct slab *slab;
 	unsigned long off;
 	size_t i;
 
@@ -474,19 +492,19 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 
 	for (i = 0; i < size; i++) {
 		if (likely(p[i])) {
-			page = virt_to_head_page(p[i]);
+			slab = virt_to_slab(p[i]);
 
-			if (!page_objcgs(page) &&
-			    memcg_alloc_page_obj_cgroups(page, s, flags,
+			if (!slab_objcgs(slab) &&
+			    memcg_alloc_slab_cgroups(slab, s, flags,
 							 false)) {
 				obj_cgroup_uncharge(objcg, obj_full_size(s));
 				continue;
 			}
 
-			off = obj_to_index(s, page_slab(page), p[i]);
+			off = obj_to_index(s, slab, p[i]);
 			obj_cgroup_get(objcg);
-			page_objcgs(page)[off] = objcg;
-			mod_objcg_state(objcg, page_pgdat(page),
+			slab_objcgs(slab)[off] = objcg;
+			mod_objcg_state(objcg, slab_pgdat(slab),
 					cache_vmstat_idx(s), obj_full_size(s));
 		} else {
 			obj_cgroup_uncharge(objcg, obj_full_size(s));
@@ -501,7 +519,7 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
 	struct kmem_cache *s;
 	struct obj_cgroup **objcgs;
 	struct obj_cgroup *objcg;
-	struct page *page;
+	struct slab *slab;
 	unsigned int off;
 	int i;
 
@@ -512,43 +530,52 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
 		if (unlikely(!p[i]))
 			continue;
 
-		page = virt_to_head_page(p[i]);
-		objcgs = page_objcgs_check(page);
+		slab = virt_to_slab(p[i]);
+		/* we could be given a kmalloc_large() object, skip those */
+		if (!slab)
+			continue;
+
+		objcgs = slab_objcgs(slab);
 		if (!objcgs)
 			continue;
 
 		if (!s_orig)
-			s = page->slab_cache;
+			s = slab->slab_cache;
 		else
 			s = s_orig;
 
-		off = obj_to_index(s, page_slab(page), p[i]);
+		off = obj_to_index(s, slab, p[i]);
 		objcg = objcgs[off];
 		if (!objcg)
 			continue;
 
 		objcgs[off] = NULL;
 		obj_cgroup_uncharge(objcg, obj_full_size(s));
-		mod_objcg_state(objcg, page_pgdat(page), cache_vmstat_idx(s),
+		mod_objcg_state(objcg, slab_pgdat(slab), cache_vmstat_idx(s),
 				-obj_full_size(s));
 		obj_cgroup_put(objcg);
 	}
 }
 
 #else /* CONFIG_MEMCG_KMEM */
+static inline struct obj_cgroup **slab_objcgs(struct slab *slab)
+{
+	return NULL;
+}
+
 static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
 {
 	return NULL;
 }
 
-static inline int memcg_alloc_page_obj_cgroups(struct page *page,
+static inline int memcg_alloc_slab_cgroups(struct slab *slab,
 					       struct kmem_cache *s, gfp_t gfp,
-					       bool new_page)
+					       bool new_slab)
 {
 	return 0;
 }
 
-static inline void memcg_free_page_obj_cgroups(struct page *page)
+static inline void memcg_free_slab_cgroups(struct slab *slab)
 {
 }
 
@@ -587,7 +614,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
 					 struct kmem_cache *s, gfp_t gfp)
 {
 	if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
-		memcg_alloc_page_obj_cgroups(slab_page(slab), s, gfp, true);
+		memcg_alloc_slab_cgroups(slab, s, gfp, true);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    PAGE_SIZE << order);
@@ -597,7 +624,7 @@ static __always_inline void unaccount_slab(struct slab *slab, int order,
 					   struct kmem_cache *s)
 {
 	if (memcg_kmem_enabled())
-		memcg_free_page_obj_cgroups(slab_page(slab));
+		memcg_free_slab_cgroups(slab);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    -(PAGE_SIZE << order));