memcg: use css_get/put when charging/uncharging kmem
Use css_get/put instead of mem_cgroup_get/put.
We can't do a simple replacement, because here mem_cgroup_put() is
called during mem_cgroup_css_free(), while mem_cgroup_css_free() won't
be called until css refcnt goes down to 0.
Instead we increment css refcnt in mem_cgroup_css_offline(), and then
check if there's still kmem charges. If not, css refcnt will be
decremented immediately, otherwise the refcnt will be released after the
last kmem allocation is uncahred.
[akpm@linux-foundation.org: tweak comment]
Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 80175de..bdc9582 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -406,6 +406,11 @@
static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
{
+ /*
+ * Our caller must use css_get() first, because memcg_uncharge_kmem()
+ * will call css_put() if it sees the memcg is dead.
+ */
+ smp_wmb();
if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
}
@@ -3050,8 +3055,16 @@
if (res_counter_uncharge(&memcg->kmem, size))
return;
+ /*
+ * Releases a reference taken in kmem_cgroup_css_offline in case
+ * this last uncharge is racing with the offlining code or it is
+ * outliving the memcg existence.
+ *
+ * The memory barrier imposed by test&clear is paired with the
+ * explicit one in memcg_kmem_mark_dead().
+ */
if (memcg_kmem_test_and_clear_dead(memcg))
- mem_cgroup_put(memcg);
+ css_put(&memcg->css);
}
void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
@@ -5183,14 +5196,6 @@
* starts accounting before all call sites are patched
*/
memcg_kmem_set_active(memcg);
-
- /*
- * kmem charges can outlive the cgroup. In the case of slab
- * pages, for instance, a page contain objects from various
- * processes, so it is unfeasible to migrate them away. We
- * need to reference count the memcg because of that.
- */
- mem_cgroup_get(memcg);
} else
ret = res_counter_set_limit(&memcg->kmem, val);
out:
@@ -5223,12 +5228,10 @@
goto out;
/*
- * destroy(), called if we fail, will issue static_key_slow_inc() and
- * mem_cgroup_put() if kmem is enabled. We have to either call them
- * unconditionally, or clear the KMEM_ACTIVE flag. I personally find
- * this more consistent, since it always leads to the same destroy path
+ * __mem_cgroup_free() will issue static_key_slow_dec() because this
+ * memcg is active already. If the later initialization fails then the
+ * cgroup core triggers the cleanup so we do not have to do it here.
*/
- mem_cgroup_get(memcg);
static_key_slow_inc(&memcg_kmem_enabled_key);
mutex_lock(&set_limit_mutex);
@@ -5913,23 +5916,43 @@
return mem_cgroup_sockets_init(memcg, ss);
}
-static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
+static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
mem_cgroup_sockets_destroy(memcg);
+}
+
+static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
+{
+ if (!memcg_kmem_is_active(memcg))
+ return;
+
+ /*
+ * kmem charges can outlive the cgroup. In the case of slab
+ * pages, for instance, a page contain objects from various
+ * processes. As we prevent from taking a reference for every
+ * such allocation we have to be careful when doing uncharge
+ * (see memcg_uncharge_kmem) and here during offlining.
+ *
+ * The idea is that that only the _last_ uncharge which sees
+ * the dead memcg will drop the last reference. An additional
+ * reference is taken here before the group is marked dead
+ * which is then paired with css_put during uncharge resp. here.
+ *
+ * Although this might sound strange as this path is called from
+ * css_offline() when the referencemight have dropped down to 0
+ * and shouldn't be incremented anymore (css_tryget would fail)
+ * we do not have other options because of the kmem allocations
+ * lifetime.
+ */
+ css_get(&memcg->css);
memcg_kmem_mark_dead(memcg);
if (res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0)
return;
- /*
- * Charges already down to 0, undo mem_cgroup_get() done in the charge
- * path here, being careful not to race with memcg_uncharge_kmem: it is
- * possible that the charges went down to 0 between mark_dead and the
- * res_counter read, so in that case, we don't need the put
- */
if (memcg_kmem_test_and_clear_dead(memcg))
- mem_cgroup_put(memcg);
+ css_put(&memcg->css);
}
#else
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
@@ -5937,7 +5960,11 @@
return 0;
}
-static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
+static void memcg_destroy_kmem(struct mem_cgroup *memcg)
+{
+}
+
+static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
}
#endif
@@ -6370,6 +6397,8 @@
{
struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
+ kmem_cgroup_css_offline(memcg);
+
mem_cgroup_invalidate_reclaim_iterators(memcg);
mem_cgroup_reparent_charges(memcg);
mem_cgroup_destroy_all_caches(memcg);
@@ -6379,9 +6408,8 @@
{
struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
- kmem_cgroup_destroy(memcg);
-
- mem_cgroup_put(memcg);
+ memcg_destroy_kmem(memcg);
+ __mem_cgroup_free(memcg);
}
#ifdef CONFIG_MMU