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Subject[PATCH 1/2] mm/memcontrol.c: remove meaningless while loop in mem_cgroup_iter()
Date
Currently, the iteration job in mem_cgroup_iter() all delegates
to __mem_cgroup_iter_next(), which will skip dead node.

Thus, the outer while loop in mem_cgroup_iter() is meaningless.
It could be proven by this:

1. memcg != NULL
we are done, no loop needed.
2. memcg == NULL
2.1 prev != NULL, a round-trip is done, break out, no loop.
2.2 prev == NULL, this is impossible, since prev==NULL means
the initial interation, it will returns memcg==root.

So, this patches remove this meaningless while loop.

Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
---
mm/memcontrol.c | 49 ++++++++++++++++++++++---------------------------
1 file changed, 22 insertions(+), 27 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 29501f0..e0ce15c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1212,6 +1212,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
{
struct mem_cgroup *memcg = NULL;
struct mem_cgroup *last_visited = NULL;
+ struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
+ int uninitialized_var(seq);

if (mem_cgroup_disabled())
return NULL;
@@ -1229,40 +1231,33 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
}

rcu_read_lock();
- while (!memcg) {
- struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
- int uninitialized_var(seq);
-
- if (reclaim) {
- int nid = zone_to_nid(reclaim->zone);
- int zid = zone_idx(reclaim->zone);
- struct mem_cgroup_per_zone *mz;
-
- mz = mem_cgroup_zoneinfo(root, nid, zid);
- iter = &mz->reclaim_iter[reclaim->priority];
- if (prev && reclaim->generation != iter->generation) {
- iter->last_visited = NULL;
- goto out_unlock;
- }
+ if (reclaim) {
+ int nid = zone_to_nid(reclaim->zone);
+ int zid = zone_idx(reclaim->zone);
+ struct mem_cgroup_per_zone *mz;

- last_visited = mem_cgroup_iter_load(iter, root, &seq);
+ mz = mem_cgroup_zoneinfo(root, nid, zid);
+ iter = &mz->reclaim_iter[reclaim->priority];
+ if (prev && reclaim->generation != iter->generation) {
+ iter->last_visited = NULL;
+ goto out_unlock;
}

- memcg = __mem_cgroup_iter_next(root, last_visited);
+ last_visited = mem_cgroup_iter_load(iter, root, &seq);
+ }

- if (reclaim) {
- mem_cgroup_iter_update(iter, last_visited, memcg, root,
- seq);
+ memcg = __mem_cgroup_iter_next(root, last_visited);

- if (!memcg)
- iter->generation++;
- else if (!prev && memcg)
- reclaim->generation = iter->generation;
- }
+ if (reclaim) {
+ mem_cgroup_iter_update(iter, last_visited, memcg, root,
+ seq);

- if (prev && !memcg)
- goto out_unlock;
+ if (!memcg)
+ iter->generation++;
+ else if (!prev && memcg)
+ reclaim->generation = iter->generation;
}
+
out_unlock:
rcu_read_unlock();
out_css_put:
--
1.9.0.GIT


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