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[73.93.239.127]) by smtp.gmail.com with ESMTPSA id fw12sm244233pjb.43.2021.01.05.14.58.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jan 2021 14:58:49 -0800 (PST) From: Yang Shi To: guro@fb.com, ktkhai@virtuozzo.com, 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: [v3 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Date: Tue, 5 Jan 2021 14:58:09 -0800 Message-Id: <20210105225817.1036378-4-shy828301@gmail.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210105225817.1036378-1-shy828301@gmail.com> References: <20210105225817.1036378-1-shy828301@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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); } - 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; } -- 2.26.2