[patch 1/3] mm: memcontrol: remove bogus NULL check after mem_cgroup_from_task()

[patch 1/3] mm: memcontrol: remove bogus NULL check after mem_cgroup_from_task()

[Johannes Weiner]

That function acts like a typecast - unless NULL is passed in, no NULL
can come out.  task_in_mem_cgroup() callers don't pass NULL tasks.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 23cf27cca370..bdf8520979cf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1335,7 +1335,7 @@ static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 bool task_in_mem_cgroup(struct task_struct *task,
 			const struct mem_cgroup *memcg)
 {
-	struct mem_cgroup *curr = NULL;
+	struct mem_cgroup *curr;
 	struct task_struct *p;
 	bool ret;
 
@@ -1351,8 +1351,7 @@ bool task_in_mem_cgroup(struct task_struct *task,
 		 */
 		rcu_read_lock();
 		curr = mem_cgroup_from_task(task);
-		if (curr)
-			css_get(&curr->css);
+		css_get(&curr->css);
 		rcu_read_unlock();
 	}
 	/*
-- 
2.1.2

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[patch 2/3] mm: memcontrol: pull the NULL check from __mem_cgroup_same_or_subtree()

[Johannes Weiner]

The NULL in mm_match_cgroup() comes from a possibly exiting mm->owner.
It makes a lot more sense to check where it's looked up, rather than
check for it in __mem_cgroup_same_or_subtree() where it's unexpected.

No other callsite passes NULL to __mem_cgroup_same_or_subtree().

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 5 +++--
 mm/memcontrol.c            | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ea007615e8f9..e32ab948f589 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -83,11 +83,12 @@ static inline
 bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
 {
 	struct mem_cgroup *task_memcg;
-	bool match;
+	bool match = false;
 
 	rcu_read_lock();
 	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
-	match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
+	if (task_memcg)
+		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
 	rcu_read_unlock();
 	return match;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bdf8520979cf..15b1c5110a8f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1316,7 +1316,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 {
 	if (root_memcg == memcg)
 		return true;
-	if (!root_memcg->use_hierarchy || !memcg)
+	if (!root_memcg->use_hierarchy)
 		return false;
 	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
 }
-- 
2.1.2

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Re: [patch 2/3] mm: memcontrol: pull the NULL check from __mem_cgroup_same_or_subtree()

[Vladimir Davydov]

On Fri, Oct 24, 2014 at 09:49:48AM -0400, Johannes Weiner wrote:
> The NULL in mm_match_cgroup() comes from a possibly exiting mm->owner.
> It makes a lot more sense to check where it's looked up, rather than
> check for it in __mem_cgroup_same_or_subtree() where it's unexpected.
> 
> No other callsite passes NULL to __mem_cgroup_same_or_subtree().
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>

> ---
>  include/linux/memcontrol.h | 5 +++--
>  mm/memcontrol.c            | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index ea007615e8f9..e32ab948f589 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -83,11 +83,12 @@ static inline
>  bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
>  {
>  	struct mem_cgroup *task_memcg;
> -	bool match;
> +	bool match = false;
>  
>  	rcu_read_lock();
>  	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> -	match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
> +	if (task_memcg)
> +		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
>  	rcu_read_unlock();
>  	return match;
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bdf8520979cf..15b1c5110a8f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1316,7 +1316,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
>  {
>  	if (root_memcg == memcg)
>  		return true;
> -	if (!root_memcg->use_hierarchy || !memcg)
> +	if (!root_memcg->use_hierarchy)
>  		return false;
>  	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
>  }
> -- 
> 2.1.2
> 

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Re: [patch 2/3] mm: memcontrol: pull the NULL check from __mem_cgroup_same_or_subtree()

[Michal Hocko]

On Fri 24-10-14 09:49:48, Johannes Weiner wrote:
> The NULL in mm_match_cgroup() comes from a possibly exiting mm->owner.
> It makes a lot more sense to check where it's looked up, rather than
> check for it in __mem_cgroup_same_or_subtree() where it's unexpected.
> 
> No other callsite passes NULL to __mem_cgroup_same_or_subtree().

Much better!

> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

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

> ---
>  include/linux/memcontrol.h | 5 +++--
>  mm/memcontrol.c            | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index ea007615e8f9..e32ab948f589 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -83,11 +83,12 @@ static inline
>  bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
>  {
>  	struct mem_cgroup *task_memcg;
> -	bool match;
> +	bool match = false;
>  
>  	rcu_read_lock();
>  	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> -	match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
> +	if (task_memcg)
> +		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
>  	rcu_read_unlock();
>  	return match;
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bdf8520979cf..15b1c5110a8f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1316,7 +1316,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
>  {
>  	if (root_memcg == memcg)
>  		return true;
> -	if (!root_memcg->use_hierarchy || !memcg)
> +	if (!root_memcg->use_hierarchy)
>  		return false;
>  	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
>  }
> -- 
> 2.1.2
> 

-- 
Michal Hocko
SUSE Labs

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[patch 3/3] mm: memcontrol: drop bogus RCU locking from mem_cgroup_same_or_subtree()

[Johannes Weiner]

None of the mem_cgroup_same_or_subtree() callers actually require it
to take the RCU lock, either because they hold it themselves or they
have css references.  Remove it.

To make the API change clear, rename the leftover helper to
mem_cgroup_is_descendant() to match cgroup_is_descendant().

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 13 +++++-----
 mm/memcontrol.c            | 59 +++++++++++++---------------------------------
 mm/oom_kill.c              |  4 ++--
 3 files changed, 24 insertions(+), 52 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e32ab948f589..d4575a1d6e99 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -68,10 +68,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
 struct lruvec *mem_cgroup_zone_lruvec(struct zone *, struct mem_cgroup *);
 struct lruvec *mem_cgroup_page_lruvec(struct page *, struct zone *);
 
-bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
-				  struct mem_cgroup *memcg);
-bool task_in_mem_cgroup(struct task_struct *task,
-			const struct mem_cgroup *memcg);
+bool mem_cgroup_is_descendant(struct mem_cgroup *memcg,
+			      struct mem_cgroup *root);
+bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
 
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
@@ -79,8 +78,8 @@ extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 extern struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg);
 extern struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css);
 
-static inline
-bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
+static inline bool mm_match_cgroup(struct mm_struct *mm,
+				   struct mem_cgroup *memcg)
 {
 	struct mem_cgroup *task_memcg;
 	bool match = false;
@@ -88,7 +87,7 @@ bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
 	rcu_read_lock();
 	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
 	if (task_memcg)
-		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
+		match = mem_cgroup_is_descendant(task_memcg, memcg);
 	rcu_read_unlock();
 	return match;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 15b1c5110a8f..f75b92a44ac6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1307,41 +1307,24 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
 	VM_BUG_ON((long)(*lru_size) < 0);
 }
 
-/*
- * Checks whether given mem is same or in the root_mem_cgroup's
- * hierarchy subtree
- */
-bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
-				  struct mem_cgroup *memcg)
+bool mem_cgroup_is_descendant(struct mem_cgroup *memcg, struct mem_cgroup *root)
 {
-	if (root_memcg == memcg)
+	if (root == memcg)
 		return true;
-	if (!root_memcg->use_hierarchy)
+	if (!root->use_hierarchy)
 		return false;
-	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
-}
-
-static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
-				       struct mem_cgroup *memcg)
-{
-	bool ret;
-
-	rcu_read_lock();
-	ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
-	rcu_read_unlock();
-	return ret;
+	return cgroup_is_descendant(memcg->css.cgroup, root->css.cgroup);
 }
 
-bool task_in_mem_cgroup(struct task_struct *task,
-			const struct mem_cgroup *memcg)
+bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
 {
-	struct mem_cgroup *curr;
+	struct mem_cgroup *task_memcg;
 	struct task_struct *p;
 	bool ret;
 
 	p = find_lock_task_mm(task);
 	if (p) {
-		curr = get_mem_cgroup_from_mm(p->mm);
+		task_memcg = get_mem_cgroup_from_mm(p->mm);
 		task_unlock(p);
 	} else {
 		/*
@@ -1350,18 +1333,12 @@ bool task_in_mem_cgroup(struct task_struct *task,
 		 * killed to prevent needlessly killing additional tasks.
 		 */
 		rcu_read_lock();
-		curr = mem_cgroup_from_task(task);
-		css_get(&curr->css);
+		task_memcg = mem_cgroup_from_task(task);
+		css_get(&task_memcg->css);
 		rcu_read_unlock();
 	}
-	/*
-	 * We should check use_hierarchy of "memcg" not "curr". Because checking
-	 * use_hierarchy of "curr" here make this function true if hierarchy is
-	 * enabled in "curr" and "curr" is a child of "memcg" in *cgroup*
-	 * hierarchy(even if use_hierarchy is disabled in "memcg").
-	 */
-	ret = mem_cgroup_same_or_subtree(memcg, curr);
-	css_put(&curr->css);
+	ret = mem_cgroup_is_descendant(task_memcg, memcg);
+	css_put(&task_memcg->css);
 	return ret;
 }
 
@@ -1446,8 +1423,8 @@ static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
 	if (!from)
 		goto unlock;
 
-	ret = mem_cgroup_same_or_subtree(memcg, from)
-		|| mem_cgroup_same_or_subtree(memcg, to);
+	ret = mem_cgroup_is_descendant(from, memcg) ||
+		mem_cgroup_is_descendant(to, memcg);
 unlock:
 	spin_unlock(&mc.lock);
 	return ret;
@@ -1813,12 +1790,8 @@ static int memcg_oom_wake_function(wait_queue_t *wait,
 	oom_wait_info = container_of(wait, struct oom_wait_info, wait);
 	oom_wait_memcg = oom_wait_info->memcg;
 
-	/*
-	 * Both of oom_wait_info->memcg and wake_memcg are stable under us.
-	 * Then we can use css_is_ancestor without taking care of RCU.
-	 */
-	if (!mem_cgroup_same_or_subtree(oom_wait_memcg, wake_memcg)
-		&& !mem_cgroup_same_or_subtree(wake_memcg, oom_wait_memcg))
+	if (!mem_cgroup_is_descendant(wake_memcg, oom_wait_memcg) &&
+	    !mem_cgroup_is_descendant(oom_wait_memcg, wake_memcg))
 		return 0;
 	return autoremove_wake_function(wait, mode, sync, arg);
 }
@@ -2138,7 +2111,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
 		memcg = stock->cached;
 		if (!memcg || !stock->nr_pages)
 			continue;
-		if (!mem_cgroup_same_or_subtree(root_memcg, memcg))
+		if (!mem_cgroup_is_descendant(memcg, root_memcg))
 			continue;
 		if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
 			if (cpu == curcpu)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 3348280eef89..864bba992735 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -119,7 +119,7 @@ found:
 
 /* return true if the task is not adequate as candidate victim task. */
 static bool oom_unkillable_task(struct task_struct *p,
-		const struct mem_cgroup *memcg, const nodemask_t *nodemask)
+		struct mem_cgroup *memcg, const nodemask_t *nodemask)
 {
 	if (is_global_init(p))
 		return true;
@@ -353,7 +353,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
  * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
  * swapents, oom_score_adj value, and name.
  */
-static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
+static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
 {
 	struct task_struct *p;
 	struct task_struct *task;
-- 
2.1.2

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Re: [patch 3/3] mm: memcontrol: drop bogus RCU locking from mem_cgroup_same_or_subtree()

[Vladimir Davydov]

On Fri, Oct 24, 2014 at 09:49:49AM -0400, Johannes Weiner wrote:
> None of the mem_cgroup_same_or_subtree() callers actually require it
> to take the RCU lock, either because they hold it themselves or they
> have css references.  Remove it.

It seems we don't need these rcu_read_lock/unlock there since commit
b47f77b5a224 ("memcg: convert to use cgroup_is_descendant()"), which
removed RCU-ish css_is_ancestor() from mem_cgroup_same_or_subtree().

Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>

> 
> To make the API change clear, rename the leftover helper to
> mem_cgroup_is_descendant() to match cgroup_is_descendant().
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h | 13 +++++-----
>  mm/memcontrol.c            | 59 +++++++++++++---------------------------------
>  mm/oom_kill.c              |  4 ++--
>  3 files changed, 24 insertions(+), 52 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index e32ab948f589..d4575a1d6e99 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -68,10 +68,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
>  struct lruvec *mem_cgroup_zone_lruvec(struct zone *, struct mem_cgroup *);
>  struct lruvec *mem_cgroup_page_lruvec(struct page *, struct zone *);
>  
> -bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				  struct mem_cgroup *memcg);
> -bool task_in_mem_cgroup(struct task_struct *task,
> -			const struct mem_cgroup *memcg);
> +bool mem_cgroup_is_descendant(struct mem_cgroup *memcg,
> +			      struct mem_cgroup *root);
> +bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
>  
>  extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
>  extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
> @@ -79,8 +78,8 @@ extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>  extern struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg);
>  extern struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css);
>  
> -static inline
> -bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
> +static inline bool mm_match_cgroup(struct mm_struct *mm,
> +				   struct mem_cgroup *memcg)
>  {
>  	struct mem_cgroup *task_memcg;
>  	bool match = false;
> @@ -88,7 +87,7 @@ bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
>  	rcu_read_lock();
>  	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
>  	if (task_memcg)
> -		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
> +		match = mem_cgroup_is_descendant(task_memcg, memcg);
>  	rcu_read_unlock();
>  	return match;
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 15b1c5110a8f..f75b92a44ac6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1307,41 +1307,24 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
>  	VM_BUG_ON((long)(*lru_size) < 0);
>  }
>  
> -/*
> - * Checks whether given mem is same or in the root_mem_cgroup's
> - * hierarchy subtree
> - */
> -bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				  struct mem_cgroup *memcg)
> +bool mem_cgroup_is_descendant(struct mem_cgroup *memcg, struct mem_cgroup *root)
>  {
> -	if (root_memcg == memcg)
> +	if (root == memcg)
>  		return true;
> -	if (!root_memcg->use_hierarchy)
> +	if (!root->use_hierarchy)
>  		return false;
> -	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
> -}
> -
> -static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				       struct mem_cgroup *memcg)
> -{
> -	bool ret;
> -
> -	rcu_read_lock();
> -	ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
> -	rcu_read_unlock();
> -	return ret;
> +	return cgroup_is_descendant(memcg->css.cgroup, root->css.cgroup);
>  }
>  
> -bool task_in_mem_cgroup(struct task_struct *task,
> -			const struct mem_cgroup *memcg)
> +bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *curr;
> +	struct mem_cgroup *task_memcg;
>  	struct task_struct *p;
>  	bool ret;
>  
>  	p = find_lock_task_mm(task);
>  	if (p) {
> -		curr = get_mem_cgroup_from_mm(p->mm);
> +		task_memcg = get_mem_cgroup_from_mm(p->mm);
>  		task_unlock(p);
>  	} else {
>  		/*
> @@ -1350,18 +1333,12 @@ bool task_in_mem_cgroup(struct task_struct *task,
>  		 * killed to prevent needlessly killing additional tasks.
>  		 */
>  		rcu_read_lock();
> -		curr = mem_cgroup_from_task(task);
> -		css_get(&curr->css);
> +		task_memcg = mem_cgroup_from_task(task);
> +		css_get(&task_memcg->css);
>  		rcu_read_unlock();
>  	}
> -	/*
> -	 * We should check use_hierarchy of "memcg" not "curr". Because checking
> -	 * use_hierarchy of "curr" here make this function true if hierarchy is
> -	 * enabled in "curr" and "curr" is a child of "memcg" in *cgroup*
> -	 * hierarchy(even if use_hierarchy is disabled in "memcg").
> -	 */
> -	ret = mem_cgroup_same_or_subtree(memcg, curr);
> -	css_put(&curr->css);
> +	ret = mem_cgroup_is_descendant(task_memcg, memcg);
> +	css_put(&task_memcg->css);
>  	return ret;
>  }
>  
> @@ -1446,8 +1423,8 @@ static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
>  	if (!from)
>  		goto unlock;
>  
> -	ret = mem_cgroup_same_or_subtree(memcg, from)
> -		|| mem_cgroup_same_or_subtree(memcg, to);
> +	ret = mem_cgroup_is_descendant(from, memcg) ||
> +		mem_cgroup_is_descendant(to, memcg);
>  unlock:
>  	spin_unlock(&mc.lock);
>  	return ret;
> @@ -1813,12 +1790,8 @@ static int memcg_oom_wake_function(wait_queue_t *wait,
>  	oom_wait_info = container_of(wait, struct oom_wait_info, wait);
>  	oom_wait_memcg = oom_wait_info->memcg;
>  
> -	/*
> -	 * Both of oom_wait_info->memcg and wake_memcg are stable under us.
> -	 * Then we can use css_is_ancestor without taking care of RCU.
> -	 */
> -	if (!mem_cgroup_same_or_subtree(oom_wait_memcg, wake_memcg)
> -		&& !mem_cgroup_same_or_subtree(wake_memcg, oom_wait_memcg))
> +	if (!mem_cgroup_is_descendant(wake_memcg, oom_wait_memcg) &&
> +	    !mem_cgroup_is_descendant(oom_wait_memcg, wake_memcg))
>  		return 0;
>  	return autoremove_wake_function(wait, mode, sync, arg);
>  }
> @@ -2138,7 +2111,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
>  		memcg = stock->cached;
>  		if (!memcg || !stock->nr_pages)
>  			continue;
> -		if (!mem_cgroup_same_or_subtree(root_memcg, memcg))
> +		if (!mem_cgroup_is_descendant(memcg, root_memcg))
>  			continue;
>  		if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
>  			if (cpu == curcpu)
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 3348280eef89..864bba992735 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -119,7 +119,7 @@ found:
>  
>  /* return true if the task is not adequate as candidate victim task. */
>  static bool oom_unkillable_task(struct task_struct *p,
> -		const struct mem_cgroup *memcg, const nodemask_t *nodemask)
> +		struct mem_cgroup *memcg, const nodemask_t *nodemask)
>  {
>  	if (is_global_init(p))
>  		return true;
> @@ -353,7 +353,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
>   * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
>   * swapents, oom_score_adj value, and name.
>   */
> -static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
> +static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
>  {
>  	struct task_struct *p;
>  	struct task_struct *task;
> -- 
> 2.1.2
> 

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Re: [patch 3/3] mm: memcontrol: drop bogus RCU locking from mem_cgroup_same_or_subtree()

[Michal Hocko]

On Fri 24-10-14 09:49:49, Johannes Weiner wrote:
> None of the mem_cgroup_same_or_subtree() callers actually require it
> to take the RCU lock, either because they hold it themselves or they
> have css references.  Remove it.
> 
> To make the API change clear, rename the leftover helper to
> mem_cgroup_is_descendant() to match cgroup_is_descendant().

Looks good.

> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

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

> ---
>  include/linux/memcontrol.h | 13 +++++-----
>  mm/memcontrol.c            | 59 +++++++++++++---------------------------------
>  mm/oom_kill.c              |  4 ++--
>  3 files changed, 24 insertions(+), 52 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index e32ab948f589..d4575a1d6e99 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -68,10 +68,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
>  struct lruvec *mem_cgroup_zone_lruvec(struct zone *, struct mem_cgroup *);
>  struct lruvec *mem_cgroup_page_lruvec(struct page *, struct zone *);
>  
> -bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				  struct mem_cgroup *memcg);
> -bool task_in_mem_cgroup(struct task_struct *task,
> -			const struct mem_cgroup *memcg);
> +bool mem_cgroup_is_descendant(struct mem_cgroup *memcg,
> +			      struct mem_cgroup *root);
> +bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg);
>  
>  extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
>  extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
> @@ -79,8 +78,8 @@ extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>  extern struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg);
>  extern struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css);
>  
> -static inline
> -bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
> +static inline bool mm_match_cgroup(struct mm_struct *mm,
> +				   struct mem_cgroup *memcg)
>  {
>  	struct mem_cgroup *task_memcg;
>  	bool match = false;
> @@ -88,7 +87,7 @@ bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
>  	rcu_read_lock();
>  	task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
>  	if (task_memcg)
> -		match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
> +		match = mem_cgroup_is_descendant(task_memcg, memcg);
>  	rcu_read_unlock();
>  	return match;
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 15b1c5110a8f..f75b92a44ac6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1307,41 +1307,24 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
>  	VM_BUG_ON((long)(*lru_size) < 0);
>  }
>  
> -/*
> - * Checks whether given mem is same or in the root_mem_cgroup's
> - * hierarchy subtree
> - */
> -bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				  struct mem_cgroup *memcg)
> +bool mem_cgroup_is_descendant(struct mem_cgroup *memcg, struct mem_cgroup *root)
>  {
> -	if (root_memcg == memcg)
> +	if (root == memcg)
>  		return true;
> -	if (!root_memcg->use_hierarchy)
> +	if (!root->use_hierarchy)
>  		return false;
> -	return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
> -}
> -
> -static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> -				       struct mem_cgroup *memcg)
> -{
> -	bool ret;
> -
> -	rcu_read_lock();
> -	ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
> -	rcu_read_unlock();
> -	return ret;
> +	return cgroup_is_descendant(memcg->css.cgroup, root->css.cgroup);
>  }
>  
> -bool task_in_mem_cgroup(struct task_struct *task,
> -			const struct mem_cgroup *memcg)
> +bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *curr;
> +	struct mem_cgroup *task_memcg;
>  	struct task_struct *p;
>  	bool ret;
>  
>  	p = find_lock_task_mm(task);
>  	if (p) {
> -		curr = get_mem_cgroup_from_mm(p->mm);
> +		task_memcg = get_mem_cgroup_from_mm(p->mm);
>  		task_unlock(p);
>  	} else {
>  		/*
> @@ -1350,18 +1333,12 @@ bool task_in_mem_cgroup(struct task_struct *task,
>  		 * killed to prevent needlessly killing additional tasks.
>  		 */
>  		rcu_read_lock();
> -		curr = mem_cgroup_from_task(task);
> -		css_get(&curr->css);
> +		task_memcg = mem_cgroup_from_task(task);
> +		css_get(&task_memcg->css);
>  		rcu_read_unlock();
>  	}
> -	/*
> -	 * We should check use_hierarchy of "memcg" not "curr". Because checking
> -	 * use_hierarchy of "curr" here make this function true if hierarchy is
> -	 * enabled in "curr" and "curr" is a child of "memcg" in *cgroup*
> -	 * hierarchy(even if use_hierarchy is disabled in "memcg").
> -	 */
> -	ret = mem_cgroup_same_or_subtree(memcg, curr);
> -	css_put(&curr->css);
> +	ret = mem_cgroup_is_descendant(task_memcg, memcg);
> +	css_put(&task_memcg->css);
>  	return ret;
>  }
>  
> @@ -1446,8 +1423,8 @@ static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
>  	if (!from)
>  		goto unlock;
>  
> -	ret = mem_cgroup_same_or_subtree(memcg, from)
> -		|| mem_cgroup_same_or_subtree(memcg, to);
> +	ret = mem_cgroup_is_descendant(from, memcg) ||
> +		mem_cgroup_is_descendant(to, memcg);
>  unlock:
>  	spin_unlock(&mc.lock);
>  	return ret;
> @@ -1813,12 +1790,8 @@ static int memcg_oom_wake_function(wait_queue_t *wait,
>  	oom_wait_info = container_of(wait, struct oom_wait_info, wait);
>  	oom_wait_memcg = oom_wait_info->memcg;
>  
> -	/*
> -	 * Both of oom_wait_info->memcg and wake_memcg are stable under us.
> -	 * Then we can use css_is_ancestor without taking care of RCU.
> -	 */
> -	if (!mem_cgroup_same_or_subtree(oom_wait_memcg, wake_memcg)
> -		&& !mem_cgroup_same_or_subtree(wake_memcg, oom_wait_memcg))
> +	if (!mem_cgroup_is_descendant(wake_memcg, oom_wait_memcg) &&
> +	    !mem_cgroup_is_descendant(oom_wait_memcg, wake_memcg))
>  		return 0;
>  	return autoremove_wake_function(wait, mode, sync, arg);
>  }
> @@ -2138,7 +2111,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
>  		memcg = stock->cached;
>  		if (!memcg || !stock->nr_pages)
>  			continue;
> -		if (!mem_cgroup_same_or_subtree(root_memcg, memcg))
> +		if (!mem_cgroup_is_descendant(memcg, root_memcg))
>  			continue;
>  		if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
>  			if (cpu == curcpu)
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 3348280eef89..864bba992735 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -119,7 +119,7 @@ found:
>  
>  /* return true if the task is not adequate as candidate victim task. */
>  static bool oom_unkillable_task(struct task_struct *p,
> -		const struct mem_cgroup *memcg, const nodemask_t *nodemask)
> +		struct mem_cgroup *memcg, const nodemask_t *nodemask)
>  {
>  	if (is_global_init(p))
>  		return true;
> @@ -353,7 +353,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
>   * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
>   * swapents, oom_score_adj value, and name.
>   */
> -static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
> +static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
>  {
>  	struct task_struct *p;
>  	struct task_struct *task;
> -- 
> 2.1.2
> 

-- 
Michal Hocko
SUSE Labs

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Re: [patch 1/3] mm: memcontrol: remove bogus NULL check after mem_cgroup_from_task()

[Vladimir Davydov]

On Fri, Oct 24, 2014 at 09:49:47AM -0400, Johannes Weiner wrote:
> That function acts like a typecast - unless NULL is passed in, no NULL
> can come out.  task_in_mem_cgroup() callers don't pass NULL tasks.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>

> ---
>  mm/memcontrol.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 23cf27cca370..bdf8520979cf 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1335,7 +1335,7 @@ static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
>  bool task_in_mem_cgroup(struct task_struct *task,
>  			const struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *curr = NULL;
> +	struct mem_cgroup *curr;
>  	struct task_struct *p;
>  	bool ret;
>  
> @@ -1351,8 +1351,7 @@ bool task_in_mem_cgroup(struct task_struct *task,
>  		 */
>  		rcu_read_lock();
>  		curr = mem_cgroup_from_task(task);
> -		if (curr)
> -			css_get(&curr->css);
> +		css_get(&curr->css);
>  		rcu_read_unlock();
>  	}
>  	/*
> -- 
> 2.1.2
> 

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Re: [patch 1/3] mm: memcontrol: remove bogus NULL check after mem_cgroup_from_task()

[Michal Hocko]

On Fri 24-10-14 09:49:47, Johannes Weiner wrote:
> That function acts like a typecast - unless NULL is passed in, no NULL
> can come out.  task_in_mem_cgroup() callers don't pass NULL tasks.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Thanks and sorry about my bogus version earlier today.

Acked-by: Michal Hocko <mhocko@suse.cz

> ---
>  mm/memcontrol.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 23cf27cca370..bdf8520979cf 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1335,7 +1335,7 @@ static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
>  bool task_in_mem_cgroup(struct task_struct *task,
>  			const struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *curr = NULL;
> +	struct mem_cgroup *curr;
>  	struct task_struct *p;
>  	bool ret;
>  
> @@ -1351,8 +1351,7 @@ bool task_in_mem_cgroup(struct task_struct *task,
>  		 */
>  		rcu_read_lock();
>  		curr = mem_cgroup_from_task(task);
> -		if (curr)
> -			css_get(&curr->css);
> +		css_get(&curr->css);
>  		rcu_read_unlock();
>  	}
>  	/*
> -- 
> 2.1.2
> 

-- 
Michal Hocko
SUSE Labs

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