diff options
| author | Kinsey Ho <kinseyho@google.com> | 2024-09-05 02:30:51 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-09-10 01:39:16 +0200 |
| commit | 4a2698b0133b5c477515ccbedff169fec722d0e7 (patch) | |
| tree | 4ae934f349450625b27ad34a5f14a75c8bbe8822 /mm/memcontrol.c | |
| parent | cgroup: clarify css sibling linkage is protected by cgroup_mutex or RCU (diff) | |
| download | linux-4a2698b0133b5c477515ccbedff169fec722d0e7.tar.xz linux-4a2698b0133b5c477515ccbedff169fec722d0e7.zip | |
mm: don't hold css->refcnt during traversal
To obtain the pointer to the next memcg position, mem_cgroup_iter()
currently holds css->refcnt during memcg traversal only to put css->refcnt
at the end of the routine. This isn't necessary as an rcu_read_lock is
already held throughout the function. The use of the RCU read lock with
css_next_descendant_pre() guarantees that sibling linkage is safe without
holding a ref on the passed-in @css.
Remove css->refcnt usage during traversal by leveraging RCU.
Link: https://lkml.kernel.org/r/20240905003058.1859929-3-kinseyho@google.com
Signed-off-by: Kinsey Ho <kinseyho@google.com>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to '')
| -rw-r--r-- | mm/memcontrol.c | 18 |
1 files changed, 1 insertions, 17 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5abff3b0cae5..8f6cf651cc79 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1013,20 +1013,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, else if (reclaim->generation != iter->generation) goto out_unlock; - while (1) { - pos = READ_ONCE(iter->position); - if (!pos || css_tryget(&pos->css)) - break; - /* - * css reference reached zero, so iter->position will - * be cleared by ->css_released. However, we should not - * rely on this happening soon, because ->css_released - * is called from a work queue, and by busy-waiting we - * might block it. So we clear iter->position right - * away. - */ - (void)cmpxchg(&iter->position, pos, NULL); - } + pos = READ_ONCE(iter->position); } else if (prev) { pos = prev; } @@ -1067,9 +1054,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, */ (void)cmpxchg(&iter->position, pos, memcg); - if (pos) - css_put(&pos->css); - if (!memcg) iter->generation++; } |