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

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On 19.05.2017 19:34, Roman Guschin wrote:
2017-05-19 15:22 GMT+01:00 Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>:
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.

 From a user's point of view the difference between "oom" and "max"
becomes really vague here,
assuming that "max" is described almost in the same words:

"The number of times the cgroup's memory usage was
about to go over the max boundary.  If direct reclaim
fails to bring it down, the OOM killer is invoked."

I wonder, if it's better to fix the existing "oom" value  to show what
it has to show, according to docs,
rather than to introduce a new one?


Nope, they are different. I think we should rephase documentation somehow

low - count of reclaims below low level
high - count of post-allocation reclaims above high level
max - count of direct reclaims
oom - count of failed direct reclaims
oom_kill - count of oom killer invocations and killed processes

+
+         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

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