[PATCH] mm: fix oom_kill event handling

[Roman Gushchin <guro@fb.com>]

Commit e27be240df53 ("mm: memcg: make sure memory.events is
uptodate when waking pollers") converted most of memcg event
counters to per-memcg atomics, which made them less confusing
for a user. The "oom_kill" counter remained untouched, so now
it behaves differently than other counters (including "oom").
This adds nothing but confusion.

Let's fix this by adding the MEMCG_OOM_KILL event, and follow
the MEMCG_OOM approach. This also removes a hack from
count_memcg_event_mm(), introduced earlier specially for the
OOM_KILL counter.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-kernel@vger.kernel.org
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
---
 include/linux/memcontrol.h | 26 ++++++++++++++++++++++----
 mm/memcontrol.c            |  6 ++++--
 mm/oom_kill.c              |  2 +-
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6cbea2f25a87..caa8b70a85f6 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -54,6 +54,7 @@ enum memcg_memory_event {
 	MEMCG_HIGH,
 	MEMCG_MAX,
 	MEMCG_OOM,
+	MEMCG_OOM_KILL,
 	MEMCG_SWAP_MAX,
 	MEMCG_SWAP_FAIL,
 	MEMCG_NR_MEMORY_EVENTS,
@@ -721,11 +722,8 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
 
 	rcu_read_lock();
 	memcg = rcu_dereference(mm->memcg);
-	if (likely(memcg)) {
+	if (likely(memcg))
 		count_memcg_events(memcg, idx, 1);
-		if (idx == OOM_KILL)
-			cgroup_file_notify(&memcg->events_file);
-	}
 	rcu_read_unlock();
 }
 
@@ -736,6 +734,21 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
 	cgroup_file_notify(&memcg->events_file);
 }
 
+static inline void memcg_memory_event_mm(struct mm_struct *mm,
+					 enum memcg_memory_event event)
+{
+	struct mem_cgroup *memcg;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
+	if (likely(memcg))
+		memcg_memory_event(memcg, event);
+	rcu_read_unlock();
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void mem_cgroup_split_huge_fixup(struct page *head);
 #endif
@@ -757,6 +770,11 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
 {
 }
 
+static inline void memcg_memory_event_mm(struct mm_struct *mm,
+					 enum memcg_memory_event event)
+{
+}
+
 static inline bool mem_cgroup_low(struct mem_cgroup *root,
 				  struct mem_cgroup *memcg)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 10973671e562..38717630305d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3772,7 +3772,8 @@ static int mem_cgroup_oom_control_read(struct seq_file *sf, void *v)
 
 	seq_printf(sf, "oom_kill_disable %d\n", memcg->oom_kill_disable);
 	seq_printf(sf, "under_oom %d\n", (bool)memcg->under_oom);
-	seq_printf(sf, "oom_kill %lu\n", memcg_sum_events(memcg, OOM_KILL));
+	seq_printf(sf, "oom_kill %lu\n",
+		   atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
 	return 0;
 }
 
@@ -5529,7 +5530,8 @@ static int memory_events_show(struct seq_file *m, void *v)
 		   atomic_long_read(&memcg->memory_events[MEMCG_MAX]));
 	seq_printf(m, "oom %lu\n",
 		   atomic_long_read(&memcg->memory_events[MEMCG_OOM]));
-	seq_printf(m, "oom_kill %lu\n", memcg_sum_events(memcg, OOM_KILL));
+	seq_printf(m, "oom_kill %lu\n",
+		   atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
 
 	return 0;
 }
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8f7d8dd99e5d..6b74142a1259 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -868,7 +868,7 @@ static void __oom_kill_process(struct task_struct *victim)
 
 	/* Raise event before sending signal: task reaper must see this */
 	count_vm_event(OOM_KILL);
-	count_memcg_event_mm(mm, OOM_KILL);
+	memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
 
 	/*
 	 * We should send SIGKILL before granting access to memory reserves
-- 
2.14.3