[RFC PATCH 11/30] mm: introduce slabobj_ext to support slab object extensions

[Suren Baghdasaryan <surenb@google.com>]

Currently slab pages can store only vectors of obj_cgroup pointers in
page->memcg_data. Introduce slabobj_ext structure to allow more data
to be stored for each slab object. Wraps obj_cgroup into slabobj_ext
to support current functionality while allowing to extend slabobj_ext
in the future.

Note: ideally the config dependency should be turned the other way around:
MEMCG should depend on SLAB_OBJ_EXT and {page|slab|folio}.memcg_data would
be renamed to something like {page|slab|folio}.objext_data. However doing
this in RFC would introduce considerable churn unrelated to the overall
idea, so avoiding this until v1.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/memcontrol.h |  18 ++++--
 init/Kconfig               |   5 ++
 mm/kfence/core.c           |   2 +-
 mm/memcontrol.c            |  60 ++++++++++---------
 mm/page_owner.c            |   2 +-
 mm/slab.h                  | 119 +++++++++++++++++++++++++------------
 6 files changed, 131 insertions(+), 75 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6257867fbf95..315399f77173 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -227,6 +227,14 @@ struct obj_cgroup {
 	};
 };
 
+/*
+ * Extended information for slab objects stored as an array in page->memcg_data
+ * if MEMCG_DATA_OBJEXTS is set.
+ */
+struct slabobj_ext {
+	struct obj_cgroup *objcg;
+} __aligned(8);
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
@@ -363,7 +371,7 @@ extern struct mem_cgroup *root_mem_cgroup;
 
 enum page_memcg_data_flags {
 	/* page->memcg_data is a pointer to an objcgs vector */
-	MEMCG_DATA_OBJCGS = (1UL << 0),
+	MEMCG_DATA_OBJEXTS = (1UL << 0),
 	/* page has been accounted as a non-slab kernel page */
 	MEMCG_DATA_KMEM = (1UL << 1),
 	/* the next bit after the last actual flag */
@@ -401,7 +409,7 @@ static inline struct mem_cgroup *__folio_memcg(struct folio *folio)
 	unsigned long memcg_data = folio->memcg_data;
 
 	VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
-	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJCGS, folio);
+	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_KMEM, folio);
 
 	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
@@ -422,7 +430,7 @@ static inline struct obj_cgroup *__folio_objcg(struct folio *folio)
 	unsigned long memcg_data = folio->memcg_data;
 
 	VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
-	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJCGS, folio);
+	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	VM_BUG_ON_FOLIO(!(memcg_data & MEMCG_DATA_KMEM), folio);
 
 	return (struct obj_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
@@ -517,7 +525,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
 	 */
 	unsigned long memcg_data = READ_ONCE(page->memcg_data);
 
-	if (memcg_data & MEMCG_DATA_OBJCGS)
+	if (memcg_data & MEMCG_DATA_OBJEXTS)
 		return NULL;
 
 	if (memcg_data & MEMCG_DATA_KMEM) {
@@ -556,7 +564,7 @@ static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *ob
 static inline bool folio_memcg_kmem(struct folio *folio)
 {
 	VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page);
-	VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJCGS, folio);
+	VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	return folio->memcg_data & MEMCG_DATA_KMEM;
 }
 
diff --git a/init/Kconfig b/init/Kconfig
index 532362fcfe31..82396d7a2717 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -958,6 +958,10 @@ config MEMCG
 	help
 	  Provides control over the memory footprint of tasks in a cgroup.
 
+config SLAB_OBJ_EXT
+	bool
+	depends on MEMCG
+
 config MEMCG_SWAP
 	bool
 	depends on MEMCG && SWAP
@@ -966,6 +970,7 @@ config MEMCG_SWAP
 config MEMCG_KMEM
 	bool
 	depends on MEMCG && !SLOB
+	select SLAB_OBJ_EXT
 	default y
 
 config BLK_CGROUP
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index c252081b11df..c0958e4a32e2 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -569,7 +569,7 @@ static unsigned long kfence_init_pool(void)
 		__folio_set_slab(slab_folio(slab));
 #ifdef CONFIG_MEMCG
 		slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
-				   MEMCG_DATA_OBJCGS;
+				   MEMCG_DATA_OBJEXTS;
 #endif
 	}
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b69979c9ced5..3f407ef2f3f1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2793,7 +2793,7 @@ static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
 	folio->memcg_data = (unsigned long)memcg;
 }
 
-#ifdef CONFIG_MEMCG_KMEM
+#ifdef CONFIG_SLAB_OBJ_EXT
 /*
  * The allocated objcg pointers array is not accounted directly.
  * Moreover, it should not come from DMA buffer and is not readily
@@ -2801,38 +2801,20 @@ static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
  */
 #define OBJCGS_CLEAR_MASK	(__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)
 
-/*
- * mod_objcg_mlstate() may be called with irq enabled, so
- * mod_memcg_lruvec_state() should be used.
- */
-static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
-				     struct pglist_data *pgdat,
-				     enum node_stat_item idx, int nr)
-{
-	struct mem_cgroup *memcg;
-	struct lruvec *lruvec;
-
-	rcu_read_lock();
-	memcg = obj_cgroup_memcg(objcg);
-	lruvec = mem_cgroup_lruvec(memcg, pgdat);
-	mod_memcg_lruvec_state(lruvec, idx, nr);
-	rcu_read_unlock();
-}
-
-int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
-				 gfp_t gfp, bool new_slab)
+int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
+			gfp_t gfp, bool new_slab)
 {
 	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,
+	vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
 			   slab_nid(slab));
 	if (!vec)
 		return -ENOMEM;
 
-	memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS;
+	memcg_data = (unsigned long) vec | MEMCG_DATA_OBJEXTS;
 	if (new_slab) {
 		/*
 		 * If the slab is brand new and nobody can yet access its
@@ -2843,7 +2825,7 @@ int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
 	} else if (cmpxchg(&slab->memcg_data, 0, memcg_data)) {
 		/*
 		 * If the slab is already in use, somebody can allocate and
-		 * assign obj_cgroups in parallel. In this case the existing
+		 * assign slabobj_exts in parallel. In this case the existing
 		 * objcg vector should be reused.
 		 */
 		kfree(vec);
@@ -2853,6 +2835,26 @@ int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
 	kmemleak_not_leak(vec);
 	return 0;
 }
+#endif /* CONFIG_SLAB_OBJ_EXT */
+
+#ifdef CONFIG_MEMCG_KMEM
+/*
+ * mod_objcg_mlstate() may be called with irq enabled, so
+ * mod_memcg_lruvec_state() should be used.
+ */
+static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
+				     struct pglist_data *pgdat,
+				     enum node_stat_item idx, int nr)
+{
+	struct mem_cgroup *memcg;
+	struct lruvec *lruvec;
+
+	rcu_read_lock();
+	memcg = obj_cgroup_memcg(objcg);
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	mod_memcg_lruvec_state(lruvec, idx, nr);
+	rcu_read_unlock();
+}
 
 static __always_inline
 struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
@@ -2863,18 +2865,18 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
 	 * slab->memcg_data.
 	 */
 	if (folio_test_slab(folio)) {
-		struct obj_cgroup **objcgs;
+		struct slabobj_ext *obj_exts;
 		struct slab *slab;
 		unsigned int off;
 
 		slab = folio_slab(folio);
-		objcgs = slab_objcgs(slab);
-		if (!objcgs)
+		obj_exts = slab_obj_exts(slab);
+		if (!obj_exts)
 			return NULL;
 
 		off = obj_to_index(slab->slab_cache, slab, p);
-		if (objcgs[off])
-			return obj_cgroup_memcg(objcgs[off]);
+		if (obj_exts[off].objcg)
+			return obj_cgroup_memcg(obj_exts[off].objcg);
 
 		return NULL;
 	}
diff --git a/mm/page_owner.c b/mm/page_owner.c
index e4c6f3f1695b..fd4af1ad34b8 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -353,7 +353,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret,
 	if (!memcg_data)
 		goto out_unlock;
 
-	if (memcg_data & MEMCG_DATA_OBJCGS)
+	if (memcg_data & MEMCG_DATA_OBJEXTS)
 		ret += scnprintf(kbuf + ret, count - ret,
 				"Slab cache page\n");
 
diff --git a/mm/slab.h b/mm/slab.h
index 4ec82bec15ec..c767ce3f0fe2 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -422,36 +422,94 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
 	return false;
 }
 
+#ifdef CONFIG_SLAB_OBJ_EXT
+
+static inline bool is_kmem_only_obj_ext(void)
+{
 #ifdef CONFIG_MEMCG_KMEM
+	return sizeof(struct slabobj_ext) == sizeof(struct obj_cgroup *);
+#else
+	return false;
+#endif
+}
+
 /*
- * slab_objcgs - get the object cgroups vector associated with a slab
+ * slab_obj_exts - get the pointer to the slab object extension vector
+ * associated with a slab.
  * @slab: a pointer to the slab struct
  *
- * Returns a pointer to the object cgroups vector associated with the slab,
+ * Returns a pointer to the object extension 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)
+static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
 {
 	unsigned long memcg_data = READ_ONCE(slab->memcg_data);
 
-	VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS),
+	VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJEXTS),
 							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);
+	return (struct slabobj_ext *)(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);
+int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
+			gfp_t gfp, bool new_slab);
 
-static inline void memcg_free_slab_cgroups(struct slab *slab)
+static inline void free_slab_obj_exts(struct slab *slab)
 {
-	kfree(slab_objcgs(slab));
+	struct slabobj_ext *obj_exts;
+
+	if (!memcg_kmem_enabled() && is_kmem_only_obj_ext())
+		return;
+
+	obj_exts = slab_obj_exts(slab);
+	kfree(obj_exts);
 	slab->memcg_data = 0;
 }
 
+static inline void prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
+{
+	struct slab *slab;
+
+	/* If kmem is the only extension then the vector will be created conditionally */
+	if (is_kmem_only_obj_ext())
+		return;
+
+	slab = virt_to_slab(p);
+	if (!slab_obj_exts(slab))
+		WARN(alloc_slab_obj_exts(slab, s, flags, false),
+			"%s, %s: Failed to create slab extension vector!\n",
+			__func__, s->name);
+}
+
+#else /* CONFIG_SLAB_OBJ_EXT */
+
+static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
+{
+	return NULL;
+}
+
+static inline int alloc_slab_obj_exts(struct slab *slab,
+				      struct kmem_cache *s, gfp_t gfp,
+				      bool new_slab)
+{
+	return 0;
+}
+
+static inline void free_slab_obj_exts(struct slab *slab)
+{
+}
+
+static inline void prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
+{
+}
+
+#endif /* CONFIG_SLAB_OBJ_EXT */
+
+#ifdef CONFIG_MEMCG_KMEM
+void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
+		     enum node_stat_item idx, int nr);
+
 static inline size_t obj_full_size(struct kmem_cache *s)
 {
 	/*
@@ -519,16 +577,15 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 		if (likely(p[i])) {
 			slab = virt_to_slab(p[i]);
 
-			if (!slab_objcgs(slab) &&
-			    memcg_alloc_slab_cgroups(slab, s, flags,
-							 false)) {
+			if (!slab_obj_exts(slab) &&
+			    alloc_slab_obj_exts(slab, s, flags, false)) {
 				obj_cgroup_uncharge(objcg, obj_full_size(s));
 				continue;
 			}
 
 			off = obj_to_index(s, slab, p[i]);
 			obj_cgroup_get(objcg);
-			slab_objcgs(slab)[off] = objcg;
+			slab_obj_exts(slab)[off].objcg = objcg;
 			mod_objcg_state(objcg, slab_pgdat(slab),
 					cache_vmstat_idx(s), obj_full_size(s));
 		} else {
@@ -541,14 +598,14 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 					void **p, int objects)
 {
-	struct obj_cgroup **objcgs;
+	struct slabobj_ext *obj_exts;
 	int i;
 
 	if (!memcg_kmem_enabled())
 		return;
 
-	objcgs = slab_objcgs(slab);
-	if (!objcgs)
+	obj_exts = slab_obj_exts(slab);
+	if (!obj_exts)
 		return;
 
 	for (i = 0; i < objects; i++) {
@@ -556,11 +613,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 		unsigned int off;
 
 		off = obj_to_index(s, slab, p[i]);
-		objcg = objcgs[off];
+		objcg = obj_exts[off].objcg;
 		if (!objcg)
 			continue;
 
-		objcgs[off] = NULL;
+		obj_exts[off].objcg = NULL;
 		obj_cgroup_uncharge(objcg, obj_full_size(s));
 		mod_objcg_state(objcg, slab_pgdat(slab), cache_vmstat_idx(s),
 				-obj_full_size(s));
@@ -569,27 +626,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 }
 
 #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_slab_cgroups(struct slab *slab,
-					       struct kmem_cache *s, gfp_t gfp,
-					       bool new_slab)
-{
-	return 0;
-}
-
-static inline void memcg_free_slab_cgroups(struct slab *slab)
-{
-}
-
 static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s,
 					     struct list_lru *lru,
 					     struct obj_cgroup **objcgp,
@@ -627,7 +668,7 @@ 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_slab_cgroups(slab, s, gfp, true);
+		alloc_slab_obj_exts(slab, s, gfp, true);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    PAGE_SIZE << order);
@@ -636,8 +677,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
 static __always_inline void unaccount_slab(struct slab *slab, int order,
 					   struct kmem_cache *s)
 {
-	if (memcg_kmem_enabled())
-		memcg_free_slab_cgroups(slab);
+	free_slab_obj_exts(slab);
 
 	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
 			    -(PAGE_SIZE << order));
@@ -729,6 +769,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
 			memset(p[i], 0, s->object_size);
 		kmemleak_alloc_recursive(p[i], s->object_size, 1,
 					 s->flags, flags);
+		prepare_slab_obj_exts_hook(s, flags, p[i]);
 	}
 
 	memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
-- 
2.37.2.672.g94769d06f0-goog