[PATCH v4 2/3] mm, oom: remove redundant task_in_mem_cgroup() check

[Shakeel Butt]

oom_unkillable_task() can be called from three different contexts i.e.
global OOM, memcg OOM and oom_score procfs interface.  At the moment
oom_unkillable_task() does a task_in_mem_cgroup() check on the given
process.  Since there is no reason to perform task_in_mem_cgroup() check
for global OOM and oom_score procfs interface, those contexts provide NULL
memcg and skips the task_in_mem_cgroup() check.  However for memcg OOM
context, the oom_unkillable_task() is always called from
mem_cgroup_scan_tasks() and thus task_in_mem_cgroup() check becomes
redundant and effectively dead code. So, just remove the
task_in_mem_cgroup() check altogether.

Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Paul Jackson <pj@xxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Changelog since v3:
- Update commit message.

Changelog since v2:
- Further divided the patch into two patches.
- Incorporated the task_in_mem_cgroup() from Tetsuo.

Changelog since v1:
- Divide the patch into two patches.

 fs/proc/base.c             |  2 +-
 include/linux/memcontrol.h |  7 -------
 include/linux/oom.h        |  2 +-
 mm/memcontrol.c            | 26 --------------------------
 mm/oom_kill.c              | 19 +++++++------------
 5 files changed, 9 insertions(+), 47 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index b8d5d100ed4a..5eacce5e924a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -532,7 +532,7 @@ static int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
 	unsigned long totalpages = totalram_pages() + total_swap_pages;
 	unsigned long points = 0;
 
-	points = oom_badness(task, NULL, NULL, totalpages) *
+	points = oom_badness(task, NULL, totalpages) *
 					1000 / totalpages;
 	seq_printf(m, "%lu\n", points);
 
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 9abf31bbe53a..2cbce1fe7780 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -407,7 +407,6 @@ static inline struct lruvec *mem_cgroup_lruvec(struct pglist_data *pgdat,
 
 struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *);
 
-bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
 struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
@@ -896,12 +895,6 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
 	return true;
 }
 
-static inline bool task_in_mem_cgroup(struct task_struct *task,
-				      const struct mem_cgroup *memcg)
-{
-	return true;
-}
-
 static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 {
 	return NULL;
diff --git a/include/linux/oom.h b/include/linux/oom.h
index d07992009265..b75104690311 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -108,7 +108,7 @@ static inline vm_fault_t check_stable_address_space(struct mm_struct *mm)
 bool __oom_reap_task_mm(struct mm_struct *mm);
 
 extern unsigned long oom_badness(struct task_struct *p,
-		struct mem_cgroup *memcg, const nodemask_t *nodemask,
+		const nodemask_t *nodemask,
 		unsigned long totalpages);
 
 extern bool out_of_memory(struct oom_control *oc);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7532ddcf31b2..b3f67a6b6527 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1259,32 +1259,6 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
 		*lru_size += nr_pages;
 }
 
-bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
-{
-	struct mem_cgroup *task_memcg;
-	struct task_struct *p;
-	bool ret;
-
-	p = find_lock_task_mm(task);
-	if (p) {
-		task_memcg = get_mem_cgroup_from_mm(p->mm);
-		task_unlock(p);
-	} else {
-		/*
-		 * All threads may have already detached their mm's, but the oom
-		 * killer still needs to detect if they have already been oom
-		 * killed to prevent needlessly killing additional tasks.
-		 */
-		rcu_read_lock();
-		task_memcg = mem_cgroup_from_task(task);
-		css_get(&task_memcg->css);
-		rcu_read_unlock();
-	}
-	ret = mem_cgroup_is_descendant(task_memcg, memcg);
-	css_put(&task_memcg->css);
-	return ret;
-}
-
 /**
  * mem_cgroup_margin - calculate chargeable space of a memory cgroup
  * @memcg: the memory cgroup
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a940d2aa92d6..eff879acc886 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -153,17 +153,13 @@ static inline bool is_memcg_oom(struct oom_control *oc)
 
 /* return true if the task is not adequate as candidate victim task. */
 static bool oom_unkillable_task(struct task_struct *p,
-		struct mem_cgroup *memcg, const nodemask_t *nodemask)
+				const nodemask_t *nodemask)
 {
 	if (is_global_init(p))
 		return true;
 	if (p->flags & PF_KTHREAD)
 		return true;
 
-	/* When mem_cgroup_out_of_memory() and p is not member of the group */
-	if (memcg && !task_in_mem_cgroup(p, memcg))
-		return true;
-
 	/* p may not have freeable memory in nodemask */
 	if (!has_intersects_mems_allowed(p, nodemask))
 		return true;
@@ -194,20 +190,19 @@ static bool is_dump_unreclaim_slabs(void)
  * oom_badness - heuristic function to determine which candidate task to kill
  * @p: task struct of which task we should calculate
  * @totalpages: total present RAM allowed for page allocation
- * @memcg: task's memory controller, if constrained
  * @nodemask: nodemask passed to page allocator for mempolicy ooms
  *
  * The heuristic for determining which task to kill is made to be as simple and
  * predictable as possible.  The goal is to return the highest value for the
  * task consuming the most memory to avoid subsequent oom failures.
  */
-unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
+unsigned long oom_badness(struct task_struct *p,
 			  const nodemask_t *nodemask, unsigned long totalpages)
 {
 	long points;
 	long adj;
 
-	if (oom_unkillable_task(p, memcg, nodemask))
+	if (oom_unkillable_task(p, nodemask))
 		return 0;
 
 	p = find_lock_task_mm(p);
@@ -318,7 +313,7 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
 	struct oom_control *oc = arg;
 	unsigned long points;
 
-	if (oom_unkillable_task(task, NULL, oc->nodemask))
+	if (oom_unkillable_task(task, oc->nodemask))
 		goto next;
 
 	/*
@@ -342,7 +337,7 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
 		goto select;
 	}
 
-	points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
+	points = oom_badness(task, oc->nodemask, oc->totalpages);
 	if (!points || points < oc->chosen_points)
 		goto next;
 
@@ -385,7 +380,7 @@ static int dump_task(struct task_struct *p, void *arg)
 	struct oom_control *oc = arg;
 	struct task_struct *task;
 
-	if (oom_unkillable_task(p, NULL, oc->nodemask))
+	if (oom_unkillable_task(p, oc->nodemask))
 		return 0;
 
 	task = find_lock_task_mm(p);
@@ -1083,7 +1078,7 @@ bool out_of_memory(struct oom_control *oc)
 	check_panic_on_oom(oc);
 
 	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
-	    current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
+	    current->mm && !oom_unkillable_task(current, oc->nodemask) &&
 	    current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
 		get_task_struct(current);
 		oc->chosen = current;
-- 
2.22.0.410.gd8fdbe21b5-goog