linux-kernel - Re: [patch v2 3/6] memcg: rework mem_cgroup

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Date:	Fri, 7 Dec 2012 09:12:25 -0800
From:	Ying Han <yinghan@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <htejun@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup iterators

On Fri, Dec 7, 2012 at 12:58 AM, Michal Hocko <mhocko@...e.cz> wrote:
> On Thu 06-12-12 19:43:52, Ying Han wrote:
> [...]
>> Forgot to mention, I was testing 3.7-rc6 with the two cgroup changes :
>
> Could you give a try to -mm tree as well. There are some changes for
> memcgs removal in that tree which are not in Linus's tree.

I will give a try, which patchset you have in mind so i can double check?

I didn't find the place where the css pins the memcg, which either
something i missed or not in place in my tree. I twisted the patch a
bit to make it closer to your v2 version, but instead keep the
mem_cgroup_put() as well as using css_tryget(). Again, my test is
happy with it:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f2eeee6..acec05a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1004,6 +1004,7 @@ struct mem_cgroup *mem_cgroup_iter(struct
mem_cgroup *root,
                        if (prev && reclaim->generation != iter->generation) {
                                if (last_visited) {
                                        css_put(&last_visited->css);
+                                       mem_cgroup_put(last_visited);
                                        iter->last_visited = NULL;
                                }
                                spin_unlock(&iter->iter_lock);
@@ -1041,15 +1042,22 @@ struct mem_cgroup *mem_cgroup_iter(struct
mem_cgroup *root,
                if (reclaim) {
                        struct mem_cgroup *curr = memcg;

-                       if (last_visited)
+                       if (last_visited) {
                                css_put(&last_visited->css);
+                               mem_cgroup_put(last_visited);
+                       }

                        if (css && !memcg)
                                curr = container_of(css, struct
mem_cgroup, css);

                        /* make sure that the cached memcg is not removed */
-                       if (curr)
-                               css_get(&curr->css);
+                       if (curr) {
+                               mem_cgroup_get(curr);
+                               if (!css_tryget(&curr->css)) {
+                                       mem_cgroup_put(curr);
+                                       curr = NULL;
+                               }
+                       }
                        iter->last_visited = curr;

                        if (!css)


--Ying

> --
> Michal Hocko
> SUSE Labs
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