From: Yang Shi <shy828301@gmail.com>
To: guro@fb.com, ktkhai@virtuozzo.com, vbabka@suse.cz,
shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org,
mhocko@suse.com, akpm@linux-foundation.org
Cc: shy828301@gmail.com, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
Date: Thu, 11 Mar 2021 11:08:35 -0800 [thread overview]
Message-ID: <20210311190845.9708-4-shy828301@gmail.com> (raw)
In-Reply-To: <20210311190845.9708-1-shy828301@gmail.com>
Since memcg_shrinker_map_size just can be changed under holding shrinker_rwsem
exclusively, the read side can be protected by holding read lock, so it sounds
superfluous to have a dedicated mutex.
Kirill Tkhai suggested use write lock since:
* We want the assignment to shrinker_maps is visible for shrink_slab_memcg().
* The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but
in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing
is not actually protected.
* READ lock makes alloc_shrinker_info() racy against memory allocation fail.
alloc_shrinker_info()->free_shrinker_info() may free memory right after
shrink_slab_memcg() dereferenced it. You may say
shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure,
but this is not the thing we want to remember in the future, since this
spreads modularity.
And a test with heavy paging workload didn't show write lock makes things worse.
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
mm/vmscan.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 98a44fb81f8a..b08c8d9055ae 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 free_shrinker_map_rcu(struct rcu_head *head)
{
@@ -201,8 +200,6 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
struct mem_cgroup_per_node *pn;
int nid;
- lockdep_assert_held(&memcg_shrinker_map_mutex);
-
for_each_node(nid) {
pn = memcg->nodeinfo[nid];
old = rcu_dereference_protected(pn->shrinker_map, true);
@@ -250,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
if (mem_cgroup_is_root(memcg))
return 0;
- mutex_lock(&memcg_shrinker_map_mutex);
+ down_write(&shrinker_rwsem);
size = memcg_shrinker_map_size;
for_each_node(nid) {
map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
@@ -261,7 +258,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
}
rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
}
- mutex_unlock(&memcg_shrinker_map_mutex);
+ up_write(&shrinker_rwsem);
return ret;
}
@@ -276,9 +273,10 @@ static int 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;
+
+ lockdep_assert_held(&shrinker_rwsem);
memcg = mem_cgroup_iter(NULL, NULL, NULL);
do {
@@ -287,13 +285,13 @@ static int expand_shrinker_maps(int new_id)
ret = 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;
}
--
2.26.2
next prev parent reply other threads:[~2021-03-11 19:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
2021-03-11 19:08 ` [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-03-11 19:08 ` [v10 PATCH 02/13] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-03-11 19:08 ` Yang Shi [this message]
2021-03-11 19:08 ` [v10 PATCH 04/13] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-03-11 19:08 ` [v10 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu Yang Shi
2021-03-11 19:08 ` [v10 PATCH 06/13] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-03-11 19:08 ` [v10 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper Yang Shi
2021-03-11 19:08 ` [v10 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-03-11 19:08 ` [v10 PATCH 09/13] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-03-11 19:08 ` [v10 PATCH 10/13] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-03-11 19:08 ` [v10 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-03-11 19:08 ` [v10 PATCH 12/13] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-03-11 19:08 ` [v10 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
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