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[PATCH -mm] oom: make oom_reaper_list single linked

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  [PATCH -mm] oom: make oom_reaper_list single linked Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-03-01 10:30 +0100
    Re: [PATCH -mm] oom: make oom_reaper_list single linked Michal Hocko <mhocko@kernel.org> - 2016-03-01 15:10 +0100

#1346476 — [PATCH -mm] oom: make oom_reaper_list single linked

Entries are only added/removed from oom_reaper_list at head so we can
use a single linked list and hence save a word in task_struct.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
---
 include/linux/sched.h |  2 +-
 mm/oom_kill.c         | 15 +++++++--------
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2118e963fba7..7b76e65595c3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1853,7 +1853,7 @@ struct task_struct {
 #endif
 	int pagefault_disabled;
 #ifdef CONFIG_MMU
-	struct list_head oom_reaper_list;
+	struct task_struct *oom_reaper_list;
 #endif
 /* CPU-specific state of this task */
 	struct thread_struct thread;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5d5eca9d6737..1a91d9a26bc9 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -423,7 +423,7 @@ bool oom_killer_disabled __read_mostly;
  */
 static struct task_struct *oom_reaper_th;
 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
-static LIST_HEAD(oom_reaper_list);
+static struct task_struct *oom_reaper_list;
 static DEFINE_SPINLOCK(oom_reaper_lock);
 
 
@@ -530,13 +530,11 @@ static int oom_reaper(void *unused)
 	while (true) {
 		struct task_struct *tsk = NULL;
 
-		wait_event_freezable(oom_reaper_wait,
-				     (!list_empty(&oom_reaper_list)));
+		wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
 		spin_lock(&oom_reaper_lock);
-		if (!list_empty(&oom_reaper_list)) {
-			tsk = list_first_entry(&oom_reaper_list,
-					struct task_struct, oom_reaper_list);
-			list_del(&tsk->oom_reaper_list);
+		if (oom_reaper_list != NULL) {
+			tsk = oom_reaper_list;
+			oom_reaper_list = tsk->oom_reaper_list;
 		}
 		spin_unlock(&oom_reaper_lock);
 
@@ -555,7 +553,8 @@ static void wake_oom_reaper(struct task_struct *tsk)
 	get_task_struct(tsk);
 
 	spin_lock(&oom_reaper_lock);
-	list_add(&tsk->oom_reaper_list, &oom_reaper_list);
+	tsk->oom_reaper_list = oom_reaper_list;
+	oom_reaper_list = tsk;
 	spin_unlock(&oom_reaper_lock);
 	wake_up(&oom_reaper_wait);
 }
-- 
2.1.4

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#1346638

On Tue 01-03-16 12:28:20, Vladimir Davydov wrote:
> Entries are only added/removed from oom_reaper_list at head so we can
> use a single linked list and hence save a word in task_struct.

There was a larger hole when I've checked the last time but why not.
 
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

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

Thanks!

> ---
>  include/linux/sched.h |  2 +-
>  mm/oom_kill.c         | 15 +++++++--------
>  2 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 2118e963fba7..7b76e65595c3 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1853,7 +1853,7 @@ struct task_struct {
>  #endif
>  	int pagefault_disabled;
>  #ifdef CONFIG_MMU
> -	struct list_head oom_reaper_list;
> +	struct task_struct *oom_reaper_list;
>  #endif
>  /* CPU-specific state of this task */
>  	struct thread_struct thread;
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5d5eca9d6737..1a91d9a26bc9 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -423,7 +423,7 @@ bool oom_killer_disabled __read_mostly;
>   */
>  static struct task_struct *oom_reaper_th;
>  static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
> -static LIST_HEAD(oom_reaper_list);
> +static struct task_struct *oom_reaper_list;
>  static DEFINE_SPINLOCK(oom_reaper_lock);
>  
>  
> @@ -530,13 +530,11 @@ static int oom_reaper(void *unused)
>  	while (true) {
>  		struct task_struct *tsk = NULL;
>  
> -		wait_event_freezable(oom_reaper_wait,
> -				     (!list_empty(&oom_reaper_list)));
> +		wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
>  		spin_lock(&oom_reaper_lock);
> -		if (!list_empty(&oom_reaper_list)) {
> -			tsk = list_first_entry(&oom_reaper_list,
> -					struct task_struct, oom_reaper_list);
> -			list_del(&tsk->oom_reaper_list);
> +		if (oom_reaper_list != NULL) {
> +			tsk = oom_reaper_list;
> +			oom_reaper_list = tsk->oom_reaper_list;
>  		}
>  		spin_unlock(&oom_reaper_lock);
>  
> @@ -555,7 +553,8 @@ static void wake_oom_reaper(struct task_struct *tsk)
>  	get_task_struct(tsk);
>  
>  	spin_lock(&oom_reaper_lock);
> -	list_add(&tsk->oom_reaper_list, &oom_reaper_list);
> +	tsk->oom_reaper_list = oom_reaper_list;
> +	oom_reaper_list = tsk;
>  	spin_unlock(&oom_reaper_lock);
>  	wake_up(&oom_reaper_wait);
>  }
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs

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