From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Yang Shi <shy828301@gmail.com>,
guro@fb.com, shakeelb@google.com, david@fromorbit.com,
hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [v3 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
Date: Wed, 6 Jan 2021 12:54:05 +0300 [thread overview]
Message-ID: <56d26993-1577-3747-2d89-1275d92f7a15@virtuozzo.com> (raw)
In-Reply-To: <20210105225817.1036378-4-shy828301@gmail.com>
On 06.01.2021 01:58, Yang Shi wrote:
> Since memcg_shrinker_map_size just can be changd under holding shrinker_rwsem
> exclusively, the read side can be protected by holding read lock, so it sounds
> superfluous to have a dedicated mutex. This should not exacerbate the contention
> to shrinker_rwsem since just one read side critical section is added.
>
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
> mm/vmscan.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9db7b4d6d0ae..ddb9f972f856 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -187,7 +187,6 @@ static DECLARE_RWSEM(shrinker_rwsem);
> #ifdef CONFIG_MEMCG
>
> static int memcg_shrinker_map_size;
> -static DEFINE_MUTEX(memcg_shrinker_map_mutex);
>
> static void memcg_free_shrinker_map_rcu(struct rcu_head *head)
> {
> @@ -200,8 +199,6 @@ static int memcg_expand_one_shrinker_map(struct mem_cgroup *memcg,
> struct memcg_shrinker_map *new, *old;
> int nid;
>
> - lockdep_assert_held(&memcg_shrinker_map_mutex);
> -
> for_each_node(nid) {
> old = rcu_dereference_protected(
> mem_cgroup_nodeinfo(memcg, nid)->shrinker_map, true);
> @@ -250,7 +247,7 @@ int memcg_alloc_shrinker_maps(struct mem_cgroup *memcg)
> if (mem_cgroup_is_root(memcg))
> return 0;
>
> - mutex_lock(&memcg_shrinker_map_mutex);
> + down_read(&shrinker_rwsem);
> size = memcg_shrinker_map_size;
> for_each_node(nid) {
> map = kvzalloc(sizeof(*map) + size, GFP_KERNEL);
> @@ -261,7 +258,7 @@ int memcg_alloc_shrinker_maps(struct mem_cgroup *memcg)
> }
> rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
Here we do STORE operation, and since we want the assignment is visible
for shrink_slab_memcg() under down_read(), we have to use down_write()
in memcg_alloc_shrinker_maps().
> }
> - mutex_unlock(&memcg_shrinker_map_mutex);
> + up_read(&shrinker_rwsem);
>
> return ret;
> }
> @@ -276,9 +273,8 @@ static int memcg_expand_shrinker_maps(int new_id)
> if (size <= old_size)
> return 0;
>
> - mutex_lock(&memcg_shrinker_map_mutex);
> if (!root_mem_cgroup)
> - goto unlock;
> + goto out;
>
> memcg = mem_cgroup_iter(NULL, NULL, NULL);
> do {
> @@ -287,13 +283,13 @@ static int memcg_expand_shrinker_maps(int new_id)
> ret = memcg_expand_one_shrinker_map(memcg, size, old_size);
> if (ret) {
> mem_cgroup_iter_break(NULL, memcg);
> - goto unlock;
> + goto out;
> }
> } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> -unlock:
> +out:
> if (!ret)
> memcg_shrinker_map_size = size;
> - mutex_unlock(&memcg_shrinker_map_mutex);
> +
> return ret;
> }
>
>
next prev parent reply other threads:[~2021-01-06 9:56 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 22:58 [RFC v3 PATCH 0/11] Make shrinker's nr_deferred memcg aware Yang Shi
2021-01-05 22:58 ` [v3 PATCH 01/11] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-01-05 22:58 ` [v3 PATCH 02/11] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-01-07 0:13 ` Roman Gushchin
2021-01-07 17:29 ` Yang Shi
2021-01-11 19:00 ` Yang Shi
2021-01-11 19:37 ` Roman Gushchin
2021-01-11 19:43 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2021-01-06 9:54 ` Kirill Tkhai [this message]
2021-01-11 17:08 ` Yang Shi
2021-01-11 17:33 ` Kirill Tkhai
2021-01-11 18:57 ` Yang Shi
2021-01-11 21:33 ` Kirill Tkhai
2021-01-12 21:23 ` Yang Shi
2021-01-13 18:16 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 04/11] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-01-06 10:15 ` Kirill Tkhai
2021-01-11 17:44 ` Yang Shi
2021-01-13 23:48 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 05/11] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-01-06 10:21 ` Kirill Tkhai
2021-01-11 18:17 ` Yang Shi
2021-01-11 21:37 ` Kirill Tkhai
2021-01-12 20:58 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 06/11] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-01-06 11:38 ` Kirill Tkhai
2021-01-11 18:19 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 07/11] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-01-06 11:06 ` Kirill Tkhai
2021-01-11 18:24 ` Yang Shi
2021-01-13 23:30 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-01-07 0:17 ` Roman Gushchin
2021-01-07 17:34 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-01-06 11:15 ` Kirill Tkhai
2021-01-11 18:40 ` Yang Shi
2021-01-11 21:57 ` Kirill Tkhai
2021-01-05 22:58 ` [v3 PATCH 10/11] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-01-06 11:34 ` Kirill Tkhai
2021-01-11 18:43 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
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