[PATCH 7/9] oom: make oom_reaper_list single linked

Michal Hocko
2016-03-22T11:01:47Z

From: Vladimir Davydov <vdavydov@virtuozzo.com>

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>
Acked-by: Michal Hocko <mhocko@suse.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 acb480b581e3..d118445a332e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1841,7 +1841,7 @@ 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 b38a648558f9..af75260f32c3 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -417,7 +417,7 @@ 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);

@@ -527,13 +527,11 @@ 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);

@@ -552,7 +550,8 @@ 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);
}
--
2.7.0