Re: [PATCH 3/4] memcg: get rid of percpu_charge_mutex lock

[Michal Hocko <mhocko@suse.cz>]

On Thu 21-07-11 13:47:04, Michal Hocko wrote:
> On Thu 21-07-11 19:30:51, KAMEZAWA Hiroyuki wrote:
> > On Thu, 21 Jul 2011 09:58:24 +0200
> > Michal Hocko <mhocko@suse.cz> wrote:
[...]
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2166,7 +2165,8 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
> > >  
> > >  	for_each_online_cpu(cpu) {
> > >  		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
> > > -		if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
> > > +		if (root_mem == stock->cached &&
> > > +				test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
> > >  			flush_work(&stock->work);
> > 
> > Doesn't this new check handle hierarchy ?
> > css_is_ancestor() will be required if you do this check.
> 
> Yes you are right. Will fix it. I will add a helper for the check.

Here is the patch with the helper. The above will then read 
	if (mem_cgroup_same_or_subtree(root_mem, stock->cached))

---
>From b963a9f4dac61044daac49700f84b7819d7c2f53 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Thu, 21 Jul 2011 13:54:13 +0200
Subject: [PATCH] memcg: add mem_cgroup_same_or_subtree helper

We are checking whether a given two groups are same or at least in the
same subtree of a hierarchy at several places. Let's make a helper for
it to make code easier to read.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
 mm/memcontrol.c |   29 ++++++++++++++++++-----------
 1 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8180cd9..8dbb9d6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1046,6 +1046,21 @@ void mem_cgroup_move_lists(struct page *page,
 	mem_cgroup_add_lru_list(page, to);
 }
 
+/*
+ * Checks whether given mem is same or in the root_mem's
+ * hierarchy subtree
+ */
+static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_mem,
+		struct mem_cgroup *mem)
+{
+	if (root_mem != mem) {
+		return (root_mem->use_hierarchy &&
+			css_is_ancestor(&mem->css, &root_mem->css));
+	}
+
+	return true;
+}
+
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 {
 	int ret;
@@ -1065,10 +1080,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 	 * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
 	 * hierarchy(even if use_hierarchy is disabled in "mem").
 	 */
-	if (mem->use_hierarchy)
-		ret = css_is_ancestor(&curr->css, &mem->css);
-	else
-		ret = (curr == mem);
+	ret = mem_cgroup_same_or_subtree(mem, curr);
 	css_put(&curr->css);
 	return ret;
 }
@@ -2150,13 +2162,8 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
 		mem = stock->cached;
 		if (!mem || !stock->nr_pages)
 			continue;
-		if (mem != root_mem) {
-			if (!root_mem->use_hierarchy)
-				continue;
-			/* check whether "mem" is under tree of "root_mem" */
-			if (!css_is_ancestor(&mem->css, &root_mem->css))
-				continue;
-		}
+		if (!mem_cgroup_same_or_subtree(root_mem, mem))
+			continue;
 		if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
 			schedule_work_on(cpu, &stock->work);
 	}
-- 
1.7.5.4


-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic