[PATCH] oom, oom_reaper: protect oom_reaper_list using simpler way

[PATCH] oom, oom_reaper: protect oom_reaper_list using simpler way

[Tetsuo Handa]

"oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task" tried
to protect oom_reaper_list using MMF_OOM_KILLED flag. But we can do it
by simply checking tsk->oom_reaper_list != NULL.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
---
 include/linux/sched.h | 2 --
 mm/oom_kill.c         | 8 ++------
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 888bc15..e4dc0c9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -512,8 +512,6 @@ static inline int get_dumpable(struct mm_struct *mm)
 #define MMF_HAS_UPROBES		19	/* has uprobes */
 #define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
 
-#define MMF_OOM_KILLED		21	/* OOM killer has chosen this mm */
-
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
 struct sighand_struct {
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 23b8b06..31bbdc6 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -543,7 +543,7 @@ static int oom_reaper(void *unused)
 
 static void wake_oom_reaper(struct task_struct *tsk)
 {
-	if (!oom_reaper_th)
+	if (!oom_reaper_th || tsk->oom_reaper_list)
 		return;
 
 	get_task_struct(tsk);
@@ -677,7 +677,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	unsigned int victim_points = 0;
 	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
 					      DEFAULT_RATELIMIT_BURST);
-	bool can_oom_reap;
+	bool can_oom_reap = true;
 
 	/*
 	 * If the task is already exiting, don't alarm the sysadmin or kill
@@ -739,10 +739,6 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	/* Get a reference to safely compare mm after task_unlock(victim) */
 	mm = victim->mm;
 	atomic_inc(&mm->mm_count);
-
-	/* Make sure we do not try to oom reap the mm multiple times */
-	can_oom_reap = !test_and_set_bit(MMF_OOM_KILLED, &mm->flags);
-
 	/*
 	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
 	 * the OOM victim from depleting the memory reserves from the user
-- 
1.8.3.1

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Re: [PATCH] oom, oom_reaper: protect oom_reaper_list using simpler way

[Michal Hocko]

On Wed 16-03-16 19:35:27, Tetsuo Handa wrote:
> "oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task" tried
> to protect oom_reaper_list using MMF_OOM_KILLED flag. But we can do it
> by simply checking tsk->oom_reaper_list != NULL.

I thought you would go with a replacement of the original patch but an
incremental one is also OK. Thanks this looks much more simpler

One could wonder why we do not have to check for oom_reaper_list under
the spinlock but this is not needed because the context calling
wake_oom_reaper is already synchronized.

> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Rik van Riel <riel@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  include/linux/sched.h | 2 --
>  mm/oom_kill.c         | 8 ++------
>  2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 888bc15..e4dc0c9 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -512,8 +512,6 @@ static inline int get_dumpable(struct mm_struct *mm)
>  #define MMF_HAS_UPROBES		19	/* has uprobes */
>  #define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
>  
> -#define MMF_OOM_KILLED		21	/* OOM killer has chosen this mm */
> -
>  #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
>  
>  struct sighand_struct {
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 23b8b06..31bbdc6 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -543,7 +543,7 @@ static int oom_reaper(void *unused)
>  
>  static void wake_oom_reaper(struct task_struct *tsk)
>  {
> -	if (!oom_reaper_th)
> +	if (!oom_reaper_th || tsk->oom_reaper_list)
>  		return;
>  
>  	get_task_struct(tsk);
> @@ -677,7 +677,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
>  	unsigned int victim_points = 0;
>  	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
>  					      DEFAULT_RATELIMIT_BURST);
> -	bool can_oom_reap;
> +	bool can_oom_reap = true;
>  
>  	/*
>  	 * If the task is already exiting, don't alarm the sysadmin or kill
> @@ -739,10 +739,6 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
>  	/* Get a reference to safely compare mm after task_unlock(victim) */
>  	mm = victim->mm;
>  	atomic_inc(&mm->mm_count);
> -
> -	/* Make sure we do not try to oom reap the mm multiple times */
> -	can_oom_reap = !test_and_set_bit(MMF_OOM_KILLED, &mm->flags);
> -
>  	/*
>  	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
>  	 * the OOM victim from depleting the memory reserves from the user
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs

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