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 won't be decremented
when kmem charges goes down to 0.
v2:
- added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
- revised comments as suggested by Michal
- fixed to check if kmem is activated in kmem_cgroup_css_offline()
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 66 +++++++++++++++++++++++++++++++++++----------------------
1 file changed, 41 insertions(+), 25 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63526f9..2f0d117 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3033,8 +3033,16 @@ static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
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 kmem_cgroup_css_offline.
+ */
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)
@@ -5130,14 +5138,6 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
* 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:
@@ -5170,12 +5170,10 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
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);
@@ -5858,23 +5856,39 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
return mem_cgroup_sockets_init(memcg, ss);
}
-static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
+static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
- mem_cgroup_sockets_destroy(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 when
+ * the reference has already 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);
+
+ /* see comment in memcg_uncharge_kmem() */
+ wmb();
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)
@@ -5882,7 +5896,7 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
return 0;
}
-static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
+static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
}
#endif
@@ -6315,6 +6329,8 @@ static void mem_cgroup_css_offline(struct cgroup *cont)
{
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);
@@ -6324,7 +6340,7 @@ static void mem_cgroup_css_free(struct cgroup *cont)
{
struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
- kmem_cgroup_destroy(memcg);
+ mem_cgroup_sockets_destroy(memcg);
mem_cgroup_put(memcg);
}
--
1.8.0.2
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>