From 422580c3cea7faaca67f6199375b79565d3d8ebd Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Mon, 10 Jul 2017 15:49:05 -0700 Subject: mm/oom_kill.c: add tracepoints for oom reaper-related events During the debugging of the problem described in https://lkml.org/lkml/2017/5/17/542 and fixed by Tetsuo Handa in https://lkml.org/lkml/2017/5/19/383 , I've found that the existing debug output is not really useful to understand issues related to the oom reaper. So, I assume, that adding some tracepoints might help with debugging of similar issues. Trace the following events: 1) a process is marked as an oom victim, 2) a process is added to the oom reaper list, 3) the oom reaper starts reaping process's mm, 4) the oom reaper finished reaping, 5) the oom reaper skips reaping. How it works in practice? Below is an example which show how the problem mentioned above can be found: one process is added twice to the oom_reaper list: $ cd /sys/kernel/debug/tracing $ echo "oom:mark_victim" > set_event $ echo "oom:wake_reaper" >> set_event $ echo "oom:skip_task_reaping" >> set_event $ echo "oom:start_task_reaping" >> set_event $ echo "oom:finish_task_reaping" >> set_event $ cat trace_pipe allocate-502 [001] .... 91.836405: mark_victim: pid=502 allocate-502 [001] .N.. 91.837356: wake_reaper: pid=502 allocate-502 [000] .N.. 91.871149: wake_reaper: pid=502 oom_reaper-23 [000] .... 91.871177: start_task_reaping: pid=502 oom_reaper-23 [000] .N.. 91.879511: finish_task_reaping: pid=502 oom_reaper-23 [000] .... 91.879580: skip_task_reaping: pid=502 Link: http://lkml.kernel.org/r/20170530185231.GA13412@castle Signed-off-by: Roman Gushchin Acked-by: Michal Hocko Cc: Tetsuo Handa Cc: Johannes Weiner Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'mm/oom_kill.c') diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 0e2c925e7826..9e8b4f030c1c 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -490,6 +490,7 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) if (!down_read_trylock(&mm->mmap_sem)) { ret = false; + trace_skip_task_reaping(tsk->pid); goto unlock_oom; } @@ -500,9 +501,12 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) */ if (!mmget_not_zero(mm)) { up_read(&mm->mmap_sem); + trace_skip_task_reaping(tsk->pid); goto unlock_oom; } + trace_start_task_reaping(tsk->pid); + /* * Tell all users of get_user/copy_from_user etc... that the content * is no longer stable. No barriers really needed because unmapping @@ -544,6 +548,7 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm) * put the oom_reaper out of the way. */ mmput_async(mm); + trace_finish_task_reaping(tsk->pid); unlock_oom: mutex_unlock(&oom_lock); return ret; @@ -615,6 +620,7 @@ static void wake_oom_reaper(struct task_struct *tsk) tsk->oom_reaper_list = oom_reaper_list; oom_reaper_list = tsk; spin_unlock(&oom_reaper_lock); + trace_wake_reaper(tsk->pid); wake_up(&oom_reaper_wait); } @@ -666,6 +672,7 @@ static void mark_oom_victim(struct task_struct *tsk) */ __thaw_task(tsk); atomic_inc(&oom_victims); + trace_mark_victim(tsk->pid); } /** -- cgit v1.2.3