[PATCH v2 18/28] mm: memcg/slab: charge individual slab objects instead of pages

[Roman Gushchin <guro@fb.com>]

Switch to per-object accounting of non-root slab objects.

Charging is performed using obj_cgroup API in the pre_alloc hook.
Obj_cgroup is charged with the size of the object and the size
of metadata: as now it's the size of an obj_cgroup pointer.
If the amount of memory has been charged successfully, the actual
allocation code is executed. Otherwise, -ENOMEM is returned.

In the post_alloc hook if the actual allocation succeeded,
corresponding vmstats are bumped and the obj_cgroup pointer is saved.
Otherwise, the charge is canceled.

On the free path obj_cgroup pointer is obtained and used to uncharge
the size of the releasing object.

Memcg and lruvec counters are now representing only memory used
by active slab objects and do not include the free space. The free
space is shared and doesn't belong to any specific cgroup.

Global per-node slab vmstats are still modified from (un)charge_slab_page()
functions. The idea is to keep all slab pages accounted as slab pages
on system level.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 mm/slab.h | 171 ++++++++++++++++++++++++------------------------------
 1 file changed, 75 insertions(+), 96 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index 0fdbeaf4aa8c..6585638e5be0 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -352,72 +352,6 @@ static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
 	return NULL;
 }
 
-/*
- * Charge the slab page belonging to the non-root kmem_cache.
- * Can be called for non-root kmem_caches only.
- */
-static __always_inline int memcg_charge_slab(struct page *page,
-					     gfp_t gfp, int order,
-					     struct kmem_cache *s)
-{
-	unsigned int nr_pages = 1 << order;
-	struct mem_cgroup *memcg;
-	struct lruvec *lruvec;
-	int ret;
-
-	rcu_read_lock();
-	memcg = READ_ONCE(s->memcg_params.memcg);
-	while (memcg && !css_tryget_online(&memcg->css))
-		memcg = parent_mem_cgroup(memcg);
-	rcu_read_unlock();
-
-	if (unlikely(!memcg || mem_cgroup_is_root(memcg))) {
-		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    nr_pages << PAGE_SHIFT);
-		percpu_ref_get_many(&s->memcg_params.refcnt, nr_pages);
-		return 0;
-	}
-
-	ret = memcg_kmem_charge(memcg, gfp, nr_pages);
-	if (ret)
-		goto out;
-
-	lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
-	mod_lruvec_state(lruvec, cache_vmstat_idx(s), nr_pages << PAGE_SHIFT);
-
-	percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
-out:
-	css_put(&memcg->css);
-	return ret;
-}
-
-/*
- * Uncharge a slab page belonging to a non-root kmem_cache.
- * Can be called for non-root kmem_caches only.
- */
-static __always_inline void memcg_uncharge_slab(struct page *page, int order,
-						struct kmem_cache *s)
-{
-	unsigned int nr_pages = 1 << order;
-	struct mem_cgroup *memcg;
-	struct lruvec *lruvec;
-
-	rcu_read_lock();
-	memcg = READ_ONCE(s->memcg_params.memcg);
-	if (likely(!mem_cgroup_is_root(memcg))) {
-		lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
-		mod_lruvec_state(lruvec, cache_vmstat_idx(s),
-				 -(nr_pages << PAGE_SHIFT));
-		memcg_kmem_uncharge(memcg, nr_pages);
-	} else {
-		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    -(nr_pages << PAGE_SHIFT));
-	}
-	rcu_read_unlock();
-
-	percpu_ref_put_many(&s->memcg_params.refcnt, nr_pages);
-}
-
 static inline int memcg_alloc_page_obj_cgroups(struct page *page, gfp_t gfp,
 					     unsigned int objects)
 {
@@ -437,6 +371,45 @@ static inline void memcg_free_page_obj_cgroups(struct page *page)
 	page->obj_cgroups = NULL;
 }
 
+static inline size_t obj_full_size(struct kmem_cache *s)
+{
+	/*
+	 * For each accounted object there is an extra space which is used
+	 * to store obj_cgroup membership. Charge it too.
+	 */
+	return s->size + sizeof(struct obj_cgroup *);
+}
+
+static inline struct kmem_cache *memcg_slab_pre_alloc_hook(struct kmem_cache *s,
+						struct obj_cgroup **objcgp,
+						size_t objects, gfp_t flags)
+{
+	struct kmem_cache *cachep;
+
+	cachep = memcg_kmem_get_cache(s, objcgp);
+	if (is_root_cache(cachep))
+		return s;
+
+	if (obj_cgroup_charge(*objcgp, flags, objects * obj_full_size(s))) {
+		memcg_kmem_put_cache(cachep);
+		cachep = NULL;
+	}
+
+	return cachep;
+}
+
+static inline void mod_objcg_memcg_state(struct obj_cgroup *objcg,
+					 struct pglist_data *pgdat,
+					 int idx, int nr)
+{
+	struct lruvec *lruvec;
+
+	rcu_read_lock();
+	lruvec = mem_cgroup_lruvec(obj_cgroup_memcg(objcg), pgdat);
+	mod_lruvec_memcg_state(lruvec, idx, nr);
+	rcu_read_unlock();
+}
+
 static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 					      struct obj_cgroup *objcg,
 					      size_t size, void **p)
@@ -451,6 +424,10 @@ 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;
+			mod_objcg_memcg_state(objcg, page_pgdat(page),
+					      cache_vmstat_idx(s), s->size);
+		} else {
+			obj_cgroup_uncharge(objcg, obj_full_size(s));
 		}
 	}
 	obj_cgroup_put(objcg);
@@ -469,6 +446,11 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s, struct page *page,
 	off = obj_to_index(s, page, p);
 	objcg = page_obj_cgroups(page)[off];
 	page_obj_cgroups(page)[off] = NULL;
+
+	obj_cgroup_uncharge(objcg, obj_full_size(s));
+	mod_objcg_memcg_state(objcg, page_pgdat(page), cache_vmstat_idx(s),
+			      -s->size);
+
 	obj_cgroup_put(objcg);
 }
 
@@ -510,17 +492,6 @@ static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
 	return NULL;
 }
 
-static inline int memcg_charge_slab(struct page *page, gfp_t gfp, int order,
-				    struct kmem_cache *s)
-{
-	return 0;
-}
-
-static inline void memcg_uncharge_slab(struct page *page, int order,
-				       struct kmem_cache *s)
-{
-}
-
 static inline int memcg_alloc_page_obj_cgroups(struct page *page, gfp_t gfp,
 					       unsigned int objects)
 {
@@ -531,6 +502,13 @@ static inline void memcg_free_page_obj_cgroups(struct page *page)
 {
 }
 
+static inline struct kmem_cache *memcg_slab_pre_alloc_hook(struct kmem_cache *s,
+						struct obj_cgroup **objcgp,
+						size_t objects, gfp_t flags)
+{
+	return NULL;
+}
+
 static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 					      struct obj_cgroup *objcg,
 					      size_t size, void **p)
@@ -569,32 +547,33 @@ static __always_inline int charge_slab_page(struct page *page,
 					    struct kmem_cache *s,
 					    unsigned int objects)
 {
-	int ret;
-
-	if (is_root_cache(s)) {
-		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    PAGE_SIZE << order);
-		return 0;
-	}
+#ifdef CONFIG_MEMCG_KMEM
+	if (!is_root_cache(s)) {
+		int ret;
 
-	ret = memcg_alloc_page_obj_cgroups(page, gfp, objects);
-	if (ret)
-		return ret;
+		ret = memcg_alloc_page_obj_cgroups(page, gfp, objects);
+		if (ret)
+			return ret;
 
-	return memcg_charge_slab(page, gfp, order, s);
+		percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
+	}
+#endif
+	mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
+			    PAGE_SIZE << order);
+	return 0;
 }
 
 static __always_inline void uncharge_slab_page(struct page *page, int order,
 					       struct kmem_cache *s)
 {
-	if (is_root_cache(s)) {
-		mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
-				    -(PAGE_SIZE << order));
-		return;
+#ifdef CONFIG_MEMCG_KMEM
+	if (!is_root_cache(s)) {
+		memcg_free_page_obj_cgroups(page);
+		percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
 	}
-
-	memcg_free_page_obj_cgroups(page);
-	memcg_uncharge_slab(page, order, s);
+#endif
+	mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
+			    -(PAGE_SIZE << order));
 }
 
 static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
@@ -666,7 +645,7 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
 
 	if (memcg_kmem_enabled() &&
 	    ((flags & __GFP_ACCOUNT) || (s->flags & SLAB_ACCOUNT)))
-		return memcg_kmem_get_cache(s, objcgp);
+		return memcg_slab_pre_alloc_hook(s, objcgp, size, flags);
 
 	return s;
 }
-- 
2.24.1