[PATCH] mm/oom_kill: count global and memory cgroup oom kills

[Konstantin Khlebnikov]

Show count of global oom killer invocations in /proc/vmstat and
count of oom kills inside memory cgroup in knob "memory.events"
(in memory.oom_control for v1 cgroup).

Also describe difference between "oom" and "oom_kill" in memory
cgroup documentation. Currently oom in memory cgroup kills tasks
iff shortage has happened inside page fault.

These counters helps in monitoring oom kills - for now
the only way is grepping for magic words in kernel log.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
 Documentation/cgroup-v2.txt   |   12 +++++++++++-
 include/linux/memcontrol.h    |    1 +
 include/linux/vm_event_item.h |    1 +
 mm/memcontrol.c               |    2 ++
 mm/oom_kill.c                 |    6 ++++++
 mm/vmstat.c                   |    1 +
 6 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index dc5e2dcdbef4..a742008d76aa 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -830,9 +830,19 @@ PAGE_SIZE multiple when read back.
 
 	  oom
 
+		The number of time the cgroup's memory usage was
+		reached the limit and allocation was about to fail.
+		Result could be oom kill, -ENOMEM from any syscall or
+		completely ignored in cases like disk readahead.
+		For now oom in memory cgroup kills tasks iff shortage
+		has happened inside page fault.
+
+	  oom_kill
+
 		The number of times the OOM killer has been invoked in
 		the cgroup.  This may not exactly match the number of
-		processes killed but should generally be close.
+		processes killed but should generally be close:	each
+		invocation could kill several processes at once.
 
   memory.stat
 
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 899949bbb2f9..2cdcebb78b58 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -55,6 +55,7 @@ enum memcg_event_item {
 	MEMCG_HIGH,
 	MEMCG_MAX,
 	MEMCG_OOM,
+	MEMCG_OOM_KILL,
 	MEMCG_NR_EVENTS,
 };
 
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index d84ae90ccd5c..1707e0a7d943 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -41,6 +41,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
 		PAGEOUTRUN, PGROTATED,
 		DROP_PAGECACHE, DROP_SLAB,
+		OOM_KILL,
 #ifdef CONFIG_NUMA_BALANCING
 		NUMA_PTE_UPDATES,
 		NUMA_HUGE_PTE_UPDATES,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 94172089f52f..416024837b81 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3574,6 +3574,7 @@ 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, MEMCG_OOM_KILL));
 	return 0;
 }
 
@@ -5165,6 +5166,7 @@ static int memory_events_show(struct seq_file *m, void *v)
 	seq_printf(m, "high %lu\n", memcg_sum_events(memcg, MEMCG_HIGH));
 	seq_printf(m, "max %lu\n", memcg_sum_events(memcg, MEMCG_MAX));
 	seq_printf(m, "oom %lu\n", memcg_sum_events(memcg, MEMCG_OOM));
+	seq_printf(m, "oom_kill %lu\n", memcg_sum_events(memcg, MEMCG_OOM_KILL));
 
 	return 0;
 }
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 04c9143a8625..c50bff3c3409 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -873,6 +873,12 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 		victim = p;
 	}
 
+	/* Raise event before sending signal: reaper must see this */
+	if (!is_memcg_oom(oc))
+		count_vm_event(OOM_KILL);
+	else
+		mem_cgroup_event(oc->memcg, MEMCG_OOM_KILL);
+
 	/* Get a reference to safely compare mm after task_unlock(victim) */
 	mm = victim->mm;
 	mmgrab(mm);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 76f73670200a..fe80b81a86e0 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1018,6 +1018,7 @@ const char * const vmstat_text[] = {
 
 	"drop_pagecache",
 	"drop_slab",
+	"oom_kill",
 
 #ifdef CONFIG_NUMA_BALANCING
 	"numa_pte_updates",