[PATCH FIX v0] mm: memcg/slab: Uncharge during kmem_cache_free_bulk()

[Bharata B Rao <bharata@linux.ibm.com>]

Object cgroup charging is done for all the objects during
allocation, but during freeing, uncharging ends up happening
for only one object in the case of bulk allocation/freeing.

Fix this by having a separate call to uncharge all the
objects from kmem_cache_free_bulk() and by modifying
memcg_slab_free_hook() to take care of bulk uncharging.

Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
---
 mm/slab.c |  2 +-
 mm/slab.h | 42 +++++++++++++++++++++++++++---------------
 mm/slub.c |  3 ++-
 3 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index f658e86ec8cee..5c70600d8b1cc 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3440,7 +3440,7 @@ void ___cache_free(struct kmem_cache *cachep, void *objp,
 		memset(objp, 0, cachep->object_size);
 	kmemleak_free_recursive(objp, cachep->flags);
 	objp = cache_free_debugcheck(cachep, objp, caller);
-	memcg_slab_free_hook(cachep, virt_to_head_page(objp), objp);
+	memcg_slab_free_hook(cachep, &objp, 1);
 
 	/*
 	 * Skip calling cache_free_alien() when the platform is not numa.
diff --git a/mm/slab.h b/mm/slab.h
index 6cc323f1313af..6dd4b702888a7 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -345,30 +345,42 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 	obj_cgroup_put(objcg);
 }
 
-static inline void memcg_slab_free_hook(struct kmem_cache *s, struct page *page,
-					void *p)
+static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
+					void **p, int objects)
 {
+	struct kmem_cache *s;
 	struct obj_cgroup *objcg;
+	struct page *page;
 	unsigned int off;
+	int i;
 
 	if (!memcg_kmem_enabled())
 		return;
 
-	if (!page_has_obj_cgroups(page))
-		return;
+	for (i = 0; i < objects; i++) {
+		if (unlikely(!p[i]))
+			continue;
 
-	off = obj_to_index(s, page, p);
-	objcg = page_obj_cgroups(page)[off];
-	page_obj_cgroups(page)[off] = NULL;
+		page = virt_to_head_page(p[i]);
+		if (!page_has_obj_cgroups(page))
+			continue;
 
-	if (!objcg)
-		return;
+		if (!s_orig)
+			s = page->slab_cache;
+		else
+			s = s_orig;
 
-	obj_cgroup_uncharge(objcg, obj_full_size(s));
-	mod_objcg_state(objcg, page_pgdat(page), cache_vmstat_idx(s),
-			-obj_full_size(s));
+		off = obj_to_index(s, page, p[i]);
+		objcg = page_obj_cgroups(page)[off];
+		if (!objcg)
+			continue;
 
-	obj_cgroup_put(objcg);
+		page_obj_cgroups(page)[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));
+		obj_cgroup_put(objcg);
+	}
 }
 
 #else /* CONFIG_MEMCG_KMEM */
@@ -406,8 +418,8 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
 {
 }
 
-static inline void memcg_slab_free_hook(struct kmem_cache *s, struct page *page,
-					void *p)
+static inline void memcg_slab_free_hook(struct kmem_cache *s,
+					void **p, int objects)
 {
 }
 #endif /* CONFIG_MEMCG_KMEM */
diff --git a/mm/slub.c b/mm/slub.c
index 6d3574013b2f8..0cbe67f13946e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3091,7 +3091,7 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
 	struct kmem_cache_cpu *c;
 	unsigned long tid;
 
-	memcg_slab_free_hook(s, page, head);
+	memcg_slab_free_hook(s, &head, 1);
 redo:
 	/*
 	 * Determine the currently cpus per cpu slab.
@@ -3253,6 +3253,7 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
 	if (WARN_ON(!size))
 		return;
 
+	memcg_slab_free_hook(s, p, size);
 	do {
 		struct detached_freelist df;
 
-- 
2.26.2