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 <[email protected]> --- mm/internal.h | 1 + mm/memcontrol.c | 17 +++++++---------- mm/vmscan.c | 2 +- 3 files changed, 9 insertions(+), 11 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index c43ccdddb0f6..10c79d199aaa 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -108,6 +108,7 @@ extern unsigned long highest_memmap_pfn; /* * in mm/vmscan.c: */ +extern struct rw_semaphore shrinker_rwsem; extern int isolate_lru_page(struct page *page); extern void putback_lru_page(struct page *page); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 29459a6ce1c7..ed942734235f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -394,8 +394,8 @@ DEFINE_STATIC_KEY_FALSE(memcg_kmem_enabled_key); EXPORT_SYMBOL(memcg_kmem_enabled_key); #endif +/* It is only can be changed with holding shrinker_rwsem exclusively */ static int memcg_shrinker_map_size; -static DEFINE_MUTEX(memcg_shrinker_map_mutex); static void memcg_free_shrinker_map_rcu(struct rcu_head *head) { @@ -408,8 +408,6 @@ 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); @@ -458,7 +456,7 @@ static 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_node(sizeof(*map) + size, GFP_KERNEL, nid); @@ -469,7 +467,7 @@ static 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; } @@ -484,9 +482,8 @@ 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; for_each_mem_cgroup(memcg) { if (mem_cgroup_is_root(memcg)) @@ -494,13 +491,13 @@ 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; } } -unlock: +out: if (!ret) memcg_shrinker_map_size = size; - mutex_unlock(&memcg_shrinker_map_mutex); + return ret; } diff --git a/mm/vmscan.c b/mm/vmscan.c index 48c06c48b97e..912c044301dd 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -184,7 +184,7 @@ static void set_task_reclaim_state(struct task_struct *task, } static LIST_HEAD(shrinker_list); -static DECLARE_RWSEM(shrinker_rwsem); +DECLARE_RWSEM(shrinker_rwsem); #ifdef CONFIG_MEMCG /* -- 2.26.2
