[Devel] [PATCH v4 11/19] sl[au]b: always get the cache from its page in kfree

[Glauber Costa]

struct page already have this information. If we start chaining
caches, this information will always be more trustworthy than
whatever is passed into the function

A parent pointer is added to the slub structure, so we can make sure
the freeing comes from either the right slab, or from its rightful
parent.

[ v3: added parent testing with VM_BUG_ON ]
[ v4: make it faster when kmemcg not in use ]

Signed-off-by: Glauber Costa <glommer at parallels.com>
CC: Christoph Lameter <cl at linux.com>
CC: Pekka Enberg <penberg at cs.helsinki.fi>
CC: Christoph Lameter <cl at linux.com>
CC: Pekka Enberg <penberg at cs.helsinki.fi>
CC: Michal Hocko <mhocko at suse.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
CC: Johannes Weiner <hannes at cmpxchg.org>
CC: Suleiman Souhlal <suleiman at google.com>
CC: Tejun Heo <tj at kernel.org>
---
 include/linux/memcontrol.h |  4 ++++
 mm/slab.c                  | 17 ++++++++++++++++-
 mm/slab.h                  | 13 +++++++++++++
 mm/slub.c                  | 14 ++++++++++++--
 4 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c7886aa..4c94182 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -536,6 +536,10 @@ static inline void sock_release_memcg(struct sock *sk)
 {
 }
 
+static inline bool memcg_kmem_enabled(void)
+{
+	return false;
+}
 static inline bool
 memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
 {
diff --git a/mm/slab.c b/mm/slab.c
index 98b3460..6f22067 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3911,9 +3911,24 @@ EXPORT_SYMBOL(__kmalloc);
  * Free an object which was previously allocated from this
  * cache.
  */
-void kmem_cache_free(struct kmem_cache *cachep, void *objp)
+void kmem_cache_free(struct kmem_cache *s, void *objp)
 {
 	unsigned long flags;
+	struct kmem_cache *cachep;
+
+	/*
+	 * When kmemcg is not being used, both assignments should return the
+	 * same value. but we don't want to pay the assignment price in that
+	 * case. If it is not compiled in, the compiler should be smart enough
+	 * to not do even the assignment. In that case, slab_equal_or_root
+	 * will also be a constant.
+	 */
+	if (memcg_kmem_enabled()) {
+		cachep = virt_to_cache(objp);
+		VM_BUG_ON(!slab_equal_or_root(cachep, s));
+	} else
+		cachep = s;
+
 
 	local_irq_save(flags);
 	debug_check_no_locks_freed(objp, cachep->object_size);
diff --git a/mm/slab.h b/mm/slab.h
index c35ecce..b9b5f1f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -108,6 +108,13 @@ static inline bool cache_match_memcg(struct kmem_cache *cachep,
 	return (is_root_cache(cachep) && !memcg) ||
 		(cachep->memcg_params->memcg == memcg);
 }
+
+static inline bool slab_equal_or_root(struct kmem_cache *s,
+					struct kmem_cache *p)
+{
+	return (p == s) ||
+		(s->memcg_params && (p == s->memcg_params->root_cache));
+}
 #else
 static inline bool is_root_cache(struct kmem_cache *s)
 {
@@ -119,5 +126,11 @@ static inline bool cache_match_memcg(struct kmem_cache *cachep,
 {
 	return true;
 }
+
+static inline bool slab_equal_or_root(struct kmem_cache *s,
+					struct kmem_cache *p)
+{
+	return true;
+}
 #endif
 #endif
diff --git a/mm/slub.c b/mm/slub.c
index 05aefe2..6e1a90f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2609,9 +2609,19 @@ redo:
 
 void kmem_cache_free(struct kmem_cache *s, void *x)
 {
-	struct page *page;
+	struct page *page = virt_to_head_page(x);
 
-	page = virt_to_head_page(x);
+	/*
+	 * When kmemcg is not being used, both assignments should return the
+	 * same value. but we don't want to pay the assignment price in that
+	 * case. If it is not compiled in, the compiler should be smart enough
+	 * to not do even the assignment. In that case, slab_equal_or_root
+	 * will also be a constant.
+	 */
+	if (memcg_kmem_enabled()) {
+		VM_BUG_ON(!slab_equal_or_root(page->slab, s));
+		s = page->slab;
+	}
 
 	if (kmem_cache_debug(s) && page->slab != s) {
 		pr_err("kmem_cache_free: Wrong slab cache. %s but object"
-- 
1.7.11.4