[Devel] [PATCH RH7 4/9] mm: memcontrol: fix memcg id ref counter on swap charge move

[Pavel Tikhomirov]

From: Vladimir Davydov <vdavydov at virtuozzo.com>

Since commit 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure
after many small jobs") swap entries do not pin memcg->css.refcnt
directly.  Instead, they pin memcg->id.ref.  So we should adjust the
reference counters accordingly when moving swap charges between cgroups.

Fixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after many small jobs")
Link: http://lkml.kernel.org/r/9ce297c64954a42dc90b543bc76106c4a94f07e8.1470219853.git.vdavydov@virtuozzo.com
Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
Acked-by: Michal Hocko <mhocko at suse.com>
Acked-by: Johannes Weiner <hannes at cmpxchg.org>
Cc: <stable at vger.kernel.org>	[3.19+]
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

Changes:
original patch also did:
-               css_put_many(&mc.from->css, mc.moved_swap);
+               css_put_many(&mc.to->css, mc.moved_swap);
but this change seems strange and unrelated to me, let's skip it.

https://jira.vzint.dev/browse/PSBM-147036

(cherry picked from commit 615d66c37c755c49ce022c9e5ac0875d27d2603d)
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 mm/memcontrol.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a9a1fb354d33..8b78c7c8d3e3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6674,9 +6674,9 @@ unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 	return memcg->id.id;
 }
 
-static void mem_cgroup_id_get(struct mem_cgroup *memcg)
+static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
-	atomic_inc(&memcg->id.ref);
+	atomic_add(n, &memcg->id.ref);
 }
 
 static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
@@ -6697,9 +6697,9 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
 	return memcg;
 }
 
-static void mem_cgroup_id_put(struct mem_cgroup *memcg)
+static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
-	if (atomic_dec_and_test(&memcg->id.ref)) {
+	if (atomic_sub_and_test(n, &memcg->id.ref)) {
 		idr_remove(&mem_cgroup_idr, memcg->id.id);
 		memcg->id.id = 0;
 
@@ -6708,6 +6708,16 @@ static void mem_cgroup_id_put(struct mem_cgroup *memcg)
 	}
 }
 
+static inline void mem_cgroup_id_get(struct mem_cgroup *memcg)
+{
+	mem_cgroup_id_get_many(memcg, 1);
+}
+
+static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
+{
+	mem_cgroup_id_put_many(memcg, 1);
+}
+
 /**
  * mem_cgroup_from_id - look up a memcg from a memcg id
  * @id: the memcg id to look up
@@ -7442,6 +7452,8 @@ static void __mem_cgroup_clear_mc(void)
 		if (!mem_cgroup_is_root(mc.from))
 			page_counter_uncharge(&mc.from->memsw, mc.moved_swap);
 
+		mem_cgroup_id_put_many(mc.from, mc.moved_swap);
+
 		for (i = 0; i < mc.moved_swap; i++)
 			css_put(&mc.from->css);
 
@@ -7452,7 +7464,9 @@ static void __mem_cgroup_clear_mc(void)
 			 */
 			page_counter_uncharge(&mc.to->memory, mc.moved_swap);
 		}
-		/* we've already done css_get(mc.to) */
+
+		mem_cgroup_id_get_many(mc.to, mc.moved_swap);
+
 		mc.moved_swap = 0;
 	}
 	if (do_swap_account) {
-- 
2.40.1