From: Roman Gushchin <guro@xxxxxx> 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 <guro@xxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/trace/events/oom.h | 80 +++++++++++++++++++++++++++++++++++ mm/oom_kill.c | 7 +++ 2 files changed, 87 insertions(+) diff -puN include/trace/events/oom.h~mmoom-add-tracepoints-for-oom-reaper-related-events include/trace/events/oom.h --- a/include/trace/events/oom.h~mmoom-add-tracepoints-for-oom-reaper-related-events +++ a/include/trace/events/oom.h @@ -70,6 +70,86 @@ TRACE_EVENT(reclaim_retry_zone, __entry->wmark_check) ); +TRACE_EVENT(mark_victim, + TP_PROTO(int pid), + + TP_ARGS(pid), + + TP_STRUCT__entry( + __field(int, pid) + ), + + TP_fast_assign( + __entry->pid = pid; + ), + + TP_printk("pid=%d", __entry->pid) +); + +TRACE_EVENT(wake_reaper, + TP_PROTO(int pid), + + TP_ARGS(pid), + + TP_STRUCT__entry( + __field(int, pid) + ), + + TP_fast_assign( + __entry->pid = pid; + ), + + TP_printk("pid=%d", __entry->pid) +); + +TRACE_EVENT(start_task_reaping, + TP_PROTO(int pid), + + TP_ARGS(pid), + + TP_STRUCT__entry( + __field(int, pid) + ), + + TP_fast_assign( + __entry->pid = pid; + ), + + TP_printk("pid=%d", __entry->pid) +); + +TRACE_EVENT(finish_task_reaping, + TP_PROTO(int pid), + + TP_ARGS(pid), + + TP_STRUCT__entry( + __field(int, pid) + ), + + TP_fast_assign( + __entry->pid = pid; + ), + + TP_printk("pid=%d", __entry->pid) +); + +TRACE_EVENT(skip_task_reaping, + TP_PROTO(int pid), + + TP_ARGS(pid), + + TP_STRUCT__entry( + __field(int, pid) + ), + + TP_fast_assign( + __entry->pid = pid; + ), + + TP_printk("pid=%d", __entry->pid) +); + #ifdef CONFIG_COMPACTION TRACE_EVENT(compact_retry, diff -puN mm/oom_kill.c~mmoom-add-tracepoints-for-oom-reaper-related-events mm/oom_kill.c --- a/mm/oom_kill.c~mmoom-add-tracepoints-for-oom-reaper-related-events +++ a/mm/oom_kill.c @@ -490,6 +490,7 @@ static bool __oom_reap_task_mm(struct ta 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 ta */ 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 ta * 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_ 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_ */ __thaw_task(tsk); atomic_inc(&oom_victims); + trace_mark_victim(tsk->pid); } /** _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
