2016-03-01 09:28:32

by Vladimir Davydov

Subject: [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 <[email protected]>
---
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

2016-03-01 14:01:38

by Michal Hocko

Subject: Re: [PATCH -mm] oom: make oom_reaper_list single linked

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 <[email protected]>

Acked-by: Michal Hocko <[email protected]>

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