[PATCH v4 7/7] mm: fix /proc/kpagecgroup interface for slab pages

Roman Gushchin
2019-05-14T21:55:00Z

Switching to an indirect scheme of getting mem_cgroup pointer for
!root slab pages broke /proc/kpagecgroup interface for them.

Let's fix it by learning page_cgroup_ino() how to get memcg
pointer for slab pages.

Reported-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
---
mm/memcontrol.c | 5 ++++-
mm/slab.h | 25 +++++++++++++++++++++++++
mm/slab_common.c | 1 +
3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0655639433ed..9b2413c2e9ea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -494,7 +494,10 @@ ino_t page_cgroup_ino(struct page *page)
unsigned long ino = 0;

rcu_read_lock();
- memcg = READ_ONCE(page->mem_cgroup);
+ if (PageHead(page) && PageSlab(page))
+ memcg = memcg_from_slab_page(page);
+ else
+ memcg = READ_ONCE(page->mem_cgroup);
while (memcg && !(memcg->css.flags & CSS_ONLINE))
memcg = parent_mem_cgroup(memcg);
if (memcg)
diff --git a/mm/slab.h b/mm/slab.h
index 7ba50e526d82..50fa534c0fc0 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -256,6 +256,26 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
return s->memcg_params.root_cache;
}

+/*
+ * Expects a pointer to a slab page. Please note, that PageSlab() check
+ * isn't sufficient, as it returns true also for tail compound slab pages,
+ * which do not have slab_cache pointer set.
+ * So this function assumes that the page can pass PageHead() and PageSlab()
+ * checks.
+ */
+static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
+{
+ struct kmem_cache *s;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ s = READ_ONCE(page->slab_cache);
+ if (s && !is_root_cache(s))
+ return rcu_dereference(s->memcg_params.memcg);
+
+ return NULL;
+}
+
/*
* Charge the slab page belonging to the non-root kmem_cache.
* Can be called for non-root kmem_caches only.
@@ -353,6 +373,11 @@ 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)
+{
+ return NULL;
+}
+
static inline int memcg_charge_slab(struct page *page, gfp_t gfp, int order,
struct kmem_cache *s)
{
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 354762394162..9d2a3d6245dc 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -254,6 +254,7 @@ static void memcg_unlink_cache(struct kmem_cache *s)
list_del(&s->memcg_params.kmem_caches_node);
mem_cgroup_put(rcu_dereference_protected(s->memcg_params.memcg,
lockdep_is_held(&slab_mutex)));
+ rcu_assign_pointer(s->memcg_params.memcg, NULL);
}
}
#else
--
2.20.1