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: Michal Hocko <mhocko@xxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 79 ++++++++++++++++++++++++++++++++-----------------------
1 file changed, 46 insertions(+), 33 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d8c6e5e..d80fcff 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1110,6 +1110,51 @@ 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
@@ -1172,39 +1217,7 @@ 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)
--
1.7.10.4
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