Commit 16248d8f authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

memcg: further simplify mem_cgroup_iter 



mem_cgroup_iter basically does two things currently.  It takes care of
the house keeping (reference counting, raclaim cookie) and it iterates
through a hierarchy tree (by using cgroup generic tree walk).  The code
would be much more easier to follow if we move the iteration outside of
the function (to __mem_cgrou_iter_next) so the distinction is more
clear.  This patch doesn't introduce any functional changes.

Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ying Han <yinghan@google.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 19f39402

mm/memcontrol.c

+46 −33
Original line number Diff line number Diff line
@@ -1073,6 +1073,51 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm) 
	return memcg;

}



/*

 * Returns a next (in a pre-order walk) alive memcg (with elevated css

 * ref. count) or NULL if the whole root's subtree has been visited.

 *

 * helper function to be used by mem_cgroup_iter

 */

static struct mem_cgroup *__mem_cgroup_iter_next(struct mem_cgroup *root,

		struct mem_cgroup *last_visited)

{

	struct cgroup *prev_cgroup, *next_cgroup;



	/*

	 * Root is not visited by cgroup iterators so it needs an

	 * explicit visit.

	 */

	if (!last_visited)

		return root;



	prev_cgroup = (last_visited == root) ? NULL

		: last_visited->css.cgroup;

skip_node:

	next_cgroup = cgroup_next_descendant_pre(

			prev_cgroup, root->css.cgroup);



	/*

	 * Even if we found a group we have to make sure it is

	 * alive. css && !memcg means that the groups should be

	 * skipped and we should continue the tree walk.

	 * last_visited css is safe to use because it is

	 * protected by css_get and the tree walk is rcu safe.

	 */

	if (next_cgroup) {

		struct mem_cgroup *mem = mem_cgroup_from_cont(

				next_cgroup);

		if (css_tryget(&mem->css))

			return mem;

		else {

			prev_cgroup = next_cgroup;

			goto skip_node;

		}

	}



	return NULL;

}



/**

 * mem_cgroup_iter - iterate over memory cgroup hierarchy

 * @root: hierarchy root
@@ -1153,39 +1198,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, 
			}

		}



		/*

		 * Root is not visited by cgroup iterators so it needs an

		 * explicit visit.

		 */

		if (!last_visited) {

			memcg = root;

		} else {

			struct cgroup *prev_cgroup, *next_cgroup;



			prev_cgroup = (last_visited == root) ? NULL

				: last_visited->css.cgroup;

skip_node:

			next_cgroup = cgroup_next_descendant_pre(

					prev_cgroup, root->css.cgroup);



			/*

			 * Even if we found a group we have to make sure it is

			 * alive. css && !memcg means that the groups should be

			 * skipped and we should continue the tree walk.

			 * last_visited css is safe to use because it is

			 * protected by css_get and the tree walk is rcu safe.

			 */

			if (next_cgroup) {

				struct mem_cgroup *mem = mem_cgroup_from_cont(

						next_cgroup);

				if (css_tryget(&mem->css))

					memcg = mem;

				else {

					prev_cgroup = next_cgroup;

					goto skip_node;

				}

			}

		}

		memcg = __mem_cgroup_iter_next(root, last_visited);



		if (reclaim) {

			if (last_visited)

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