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Message-ID: <20240813204716.842811-4-kinseyho@google.com>
Date: Tue, 13 Aug 2024 20:47:13 +0000
From: Kinsey Ho <kinseyho@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
Yosry Ahmed <yosryahmed@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>,
Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>, mkoutny@...e.com,
Kinsey Ho <kinseyho@...gle.com>
Subject: [PATCH mm-unstable v2 3/5] mm: increment gen # before restarting traversal
The generation number in struct mem_cgroup_reclaim_iter should be
incremented on every round-trip. Currently, it is possible for a
concurrent reclaimer to jump in at the end of the hierarchy, causing a
traversal restart (resetting the iteration position) without
incrementing the generation number.
By resetting the position without incrementing the generation, it's
possible for another ongoing mem_cgroup_iter() thread to walk the tree
twice.
Move the traversal restart such that the generation number is
incremented before the restart.
Signed-off-by: Kinsey Ho <kinseyho@...gle.com>
---
mm/memcontrol.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1688aae3b1b4..937b7efc41ca 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1036,7 +1036,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
root = root_mem_cgroup;
rcu_read_lock();
-
+restart:
if (reclaim) {
struct mem_cgroup_per_node *mz;
@@ -1063,14 +1063,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
for (;;) {
css = css_next_descendant_pre(css, &root->css);
if (!css) {
- /*
- * Reclaimers share the hierarchy walk, and a
- * new one might jump in right at the end of
- * the hierarchy - make sure they see at least
- * one group and restart from the beginning.
- */
- if (!prev)
- continue;
break;
}
@@ -1093,8 +1085,18 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
*/
(void)cmpxchg(&iter->position, pos, memcg);
- if (!memcg)
+ if (!memcg) {
iter->generation++;
+
+ /*
+ * Reclaimers share the hierarchy walk, and a
+ * new one might jump in right at the end of
+ * the hierarchy - make sure they see at least
+ * one group and restart from the beginning.
+ */
+ if (!prev)
+ goto restart;
+ }
}
out_unlock:
--
2.46.0.76.ge559c4bf1a-goog
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