[PATCH 11/16] mm: memcg/slab: replace memcg_from_slab_page() with memcg_from_slab_obj()

[Roman Gushchin <guro@xxxxxx>]

On our way to share slab pages between multiple memory cgroups
let's make sure we don't use kmem_cache.memcg_params.memcg
pointer to determine memcg ownership of a slab object/page.

Let's transform memcg_from_slab_page() into memcg_from_slab_obj(),
which relies on memcg ownership data stored in page->mem_cgroup_vec.

Delete mem_cgroup_from_kmem() and use memcg_from_slab_obj()
instead.

Note: memcg_from_slab_obj() returns NULL if slab obj belongs
to the root cgroup, so remove the redundant check in
__mod_lruvec_slab_state().

Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
 mm/list_lru.c   | 12 +-----------
 mm/memcontrol.c |  9 ++++-----
 mm/slab.h       | 21 +++++++++++++--------
 3 files changed, 18 insertions(+), 24 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 0f1f6b06b7f3..4f9d791b802c 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -57,16 +57,6 @@ list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
 	return &nlru->lru;
 }
 
-static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
-	struct page *page;
-
-	if (!memcg_kmem_enabled())
-		return NULL;
-	page = virt_to_head_page(ptr);
-	return memcg_from_slab_page(page);
-}
-
 static inline struct list_lru_one *
 list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
 		   struct mem_cgroup **memcg_ptr)
@@ -77,7 +67,7 @@ list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
 	if (!nlru->memcg_lrus)
 		goto out;
 
-	memcg = mem_cgroup_from_kmem(ptr);
+	memcg = memcg_from_slab_obj(ptr);
 	if (!memcg)
 		goto out;
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8a753a336efd..1982b14d6e6f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -548,7 +548,7 @@ ino_t page_cgroup_ino(struct page *page)
 
 	rcu_read_lock();
 	if (PageHead(page) && PageSlab(page))
-		memcg = memcg_from_slab_page(page);
+		memcg = root_mem_cgroup;
 	else
 		memcg = READ_ONCE(page->mem_cgroup);
 	while (memcg && !(memcg->css.flags & CSS_ONLINE))
@@ -852,16 +852,15 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 
 void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
 {
-	struct page *page = virt_to_head_page(p);
-	pg_data_t *pgdat = page_pgdat(page);
+	pg_data_t *pgdat = page_pgdat(virt_to_page(p));
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
 	rcu_read_lock();
-	memcg = memcg_from_slab_page(page);
+	memcg = memcg_from_slab_obj(p);
 
 	/* Untracked pages have no memcg, no lruvec. Update only the node */
-	if (!memcg || memcg == root_mem_cgroup) {
+	if (!memcg) {
 		__mod_node_page_state(pgdat, idx, val);
 	} else {
 		lruvec = mem_cgroup_lruvec(pgdat, memcg);
diff --git a/mm/slab.h b/mm/slab.h
index 0f2f712de77a..a6330065d434 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -329,15 +329,20 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
  * The kmem_cache can be reparented asynchronously. The caller must ensure
  * the memcg lifetime, e.g. by taking rcu_read_lock() or cgroup_mutex.
  */
-static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
+static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
 {
-	struct kmem_cache *s;
-
-	s = READ_ONCE(page->slab_cache);
-	if (s && !is_root_cache(s))
-		return READ_ONCE(s->memcg_params.memcg);
+	struct mem_cgroup_ptr *memcg_ptr;
+	struct page *page;
+	unsigned int off;
 
-	return NULL;
+	if (!memcg_kmem_enabled())
+		return NULL;
+	page = virt_to_head_page(ptr);
+	if (is_root_cache(page->slab_cache))
+		return NULL;
+	off = obj_to_index(page->slab_cache, page, ptr);
+	memcg_ptr = page->mem_cgroup_vec[off];
+	return memcg_ptr->memcg;
 }
 
 static inline int memcg_alloc_page_memcg_vec(struct page *page, gfp_t gfp,
@@ -464,7 +469,7 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
 	return s;
 }
 
-static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
+static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
 {
 	return NULL;
 }
-- 
2.21.0