[PATCH] oom_reaper: switch to struct list_head for reap queue

Aleksa Sarai
2017-02-14T15:06:32Z

Rather than implementing an open addressing linked list structure
ourselves, use the standard list_head structure to improve consistency
with the rest of the kernel and reduce confusion.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Aleksa Sarai <asarai@suse.de>
---
include/linux/sched.h | 6 +++++-
kernel/fork.c | 4 ++++
mm/oom_kill.c | 24 +++++++++++++-----------
3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e93594b88130..d8bcd0f8c5fe 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1960,7 +1960,11 @@ struct task_struct {
#endif
int pagefault_disabled;
#ifdef CONFIG_MMU
- struct task_struct *oom_reaper_list;
+ /*
+ * List of threads that have to be reaped by OOM (rooted at
+ * &oom_reaper_list in mm/oom_kill.c).
+ */
+ struct list_head oom_reaper_list;
#endif
#ifdef CONFIG_VMAP_STACK
struct vm_struct *stack_vm_area;
diff --git a/kernel/fork.c b/kernel/fork.c
index 5908f9fba21b..faca59865b1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1165,6 +1165,10 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
#endif

+#ifdef CONFIG_MMU
+ INIT_LIST_HEAD(&tsk->oom_reaper_list);
+#endif
+
tsk->mm = NULL;
tsk->active_mm = NULL;

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 51c091849dcb..d6b63ef52b88 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1,6 +1,6 @@
/*
* linux/mm/oom_kill.c
- *
+ *
* Copyright (C) 1998,2000 Rik van Riel
* Thanks go out to Claus Fischer for some serious inspiration and
* for goading me into coding this file...
@@ -460,7 +460,7 @@ bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
*/
static struct task_struct *oom_reaper_th;
static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
-static struct task_struct *oom_reaper_list;
+static LIST_HEAD(oom_reaper_list);
static DEFINE_SPINLOCK(oom_reaper_lock);

static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
@@ -565,7 +565,7 @@ static void oom_reap_task(struct task_struct *tsk)
debug_show_all_locks();

done:
- tsk->oom_reaper_list = NULL;
+ list_del_init(&tsk->oom_reaper_list);

/*
* Hide this mm from OOM killer because it has been either reaped or
@@ -582,12 +582,15 @@ static int oom_reaper(void *unused)
while (true) {
struct task_struct *tsk = NULL;

- wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
+ wait_event_freezable(oom_reaper_wait,
+ !list_empty(&oom_reaper_list));
+
spin_lock(&oom_reaper_lock);
- if (oom_reaper_list != NULL) {
- tsk = oom_reaper_list;
- oom_reaper_list = tsk->oom_reaper_list;
- }
+ tsk = list_first_entry_or_null(&oom_reaper_list,
+ struct task_struct,
+ oom_reaper_list);
+ if (tsk)
+ list_del_init(&tsk->oom_reaper_list);
spin_unlock(&oom_reaper_lock);

if (tsk)
@@ -603,14 +606,13 @@ static void wake_oom_reaper(struct task_struct *tsk)
return;

/* tsk is already queued? */
- if (tsk == oom_reaper_list || tsk->oom_reaper_list)
+ if (!list_empty(&tsk->oom_reaper_list))
return;

get_task_struct(tsk);

spin_lock(&oom_reaper_lock);
- tsk->oom_reaper_list = oom_reaper_list;
- oom_reaper_list = tsk;
+ list_add_tail(&tsk->oom_reaper_list, &oom_reaper_list);
spin_unlock(&oom_reaper_lock);
wake_up(&oom_reaper_wait);
}
--
2.11.0