[Cc Kirill] AFAIU this has already been fixed in exactly the same fashion by Kirill (mmotm commit 8e7d1201ec71 "mm: make counting of list_lru_one::nr_items lockless"). Kirill is working on further optimizations right now, see https://lkml.kernel.org/r/152163840790.21546.980703278415599202.stgit@localhost.localdomain On Tue, Mar 27, 2018 at 10:15:46AM +0200, Michal Hocko wrote: > [CC Dave] > > On Tue 27-03-18 15:59:04, Li RongQing wrote: > > when reclaim memory, shink_slab will take lots of time even if > > no memory is reclaimed, since list_lru_count_one called by it > > needs to take a spinlock > > > > try to optimize it by replacing spinlock with RCU in > > __list_lru_count_one > > Isn't the RCU overkill here? Why cannot we simply do an optimistic > lockless check for nr_items? It would be racy but does it actually > matter? We should be able to tolerate occasional 0 to non-zero and vice > versa transitions AFAICS. > > > > > $dd if=aaa of=bbb bs=1k count=3886080 > > $rm -f bbb > > $time echo 100000000 >/cgroup/memory/test/memory.limit_in_bytes > > > > Before: 0m0.415s ===> after: 0m0.395s > > > > Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> > > --- > > include/linux/list_lru.h | 2 ++ > > mm/list_lru.c | 69 ++++++++++++++++++++++++++++++++++-------------- > > 2 files changed, 51 insertions(+), 20 deletions(-) > > > > diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h > > index bb8129a3474d..ae472538038e 100644 > > --- a/include/linux/list_lru.h > > +++ b/include/linux/list_lru.h > > @@ -29,6 +29,7 @@ struct list_lru_one { > > struct list_head list; > > /* may become negative during memcg reparenting */ > > long nr_items; > > + struct rcu_head rcu; > > }; > > > > struct list_lru_memcg { > > @@ -46,6 +47,7 @@ struct list_lru_node { > > struct list_lru_memcg *memcg_lrus; > > #endif > > long nr_items; > > + struct rcu_head rcu; > > } ____cacheline_aligned_in_smp; > > > > struct list_lru { > > diff --git a/mm/list_lru.c b/mm/list_lru.c > > index fd41e969ede5..4c58ed861729 100644 > > --- a/mm/list_lru.c > > +++ b/mm/list_lru.c > > @@ -52,13 +52,13 @@ static inline bool list_lru_memcg_aware(struct list_lru *lru) > > static inline struct list_lru_one * > > list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx) > > { > > - /* > > - * The lock protects the array of per cgroup lists from relocation > > - * (see memcg_update_list_lru_node). > > - */ > > - lockdep_assert_held(&nlru->lock); > > - if (nlru->memcg_lrus && idx >= 0) > > - return nlru->memcg_lrus->lru[idx]; > > + struct list_lru_memcg *tmp; > > + > > + WARN_ON_ONCE(!rcu_read_lock_held()); > > + > > + tmp = rcu_dereference(nlru->memcg_lrus); > > + if (tmp && idx >= 0) > > + return rcu_dereference(tmp->lru[idx]); > > > > return &nlru->lru; > > } > > @@ -113,14 +113,17 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item) > > struct list_lru_one *l; > > > > spin_lock(&nlru->lock); > > + rcu_read_lock(); > > if (list_empty(item)) { > > l = list_lru_from_kmem(nlru, item); > > list_add_tail(item, &l->list); > > l->nr_items++; > > nlru->nr_items++; > > + rcu_read_unlock(); > > spin_unlock(&nlru->lock); > > return true; > > } > > + rcu_read_unlock(); > > spin_unlock(&nlru->lock); > > return false; > > } > > @@ -133,14 +136,17 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item) > > struct list_lru_one *l; > > > > spin_lock(&nlru->lock); > > + rcu_read_lock(); > > if (!list_empty(item)) { > > l = list_lru_from_kmem(nlru, item); > > list_del_init(item); > > l->nr_items--; > > nlru->nr_items--; > > + rcu_read_unlock(); > > spin_unlock(&nlru->lock); > > return true; > > } > > + rcu_read_unlock(); > > spin_unlock(&nlru->lock); > > return false; > > } > > @@ -166,12 +172,13 @@ static unsigned long __list_lru_count_one(struct list_lru *lru, > > { > > struct list_lru_node *nlru = &lru->node[nid]; > > struct list_lru_one *l; > > - unsigned long count; > > + unsigned long count = 0; > > > > - spin_lock(&nlru->lock); > > + rcu_read_lock(); > > l = list_lru_from_memcg_idx(nlru, memcg_idx); > > - count = l->nr_items; > > - spin_unlock(&nlru->lock); > > + if (l) > > + count = l->nr_items; > > + rcu_read_unlock(); > > > > return count; > > } > > @@ -204,6 +211,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx, > > unsigned long isolated = 0; > > > > spin_lock(&nlru->lock); > > + rcu_read_lock(); > > l = list_lru_from_memcg_idx(nlru, memcg_idx); > > restart: > > list_for_each_safe(item, n, &l->list) { > > @@ -250,6 +258,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx, > > } > > } > > > > + rcu_read_unlock(); > > spin_unlock(&nlru->lock); > > return isolated; > > } > > @@ -296,9 +305,14 @@ static void __memcg_destroy_list_lru_node(struct list_lru_memcg *memcg_lrus, > > int begin, int end) > > { > > int i; > > + struct list_lru_one *tmp; > > > > - for (i = begin; i < end; i++) > > - kfree(memcg_lrus->lru[i]); > > + for (i = begin; i < end; i++) { > > + tmp = memcg_lrus->lru[i]; > > + rcu_assign_pointer(memcg_lrus->lru[i], NULL); > > + if (tmp) > > + kfree_rcu(tmp, rcu); > > + } > > } > > > > static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus, > > @@ -314,7 +328,7 @@ static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus, > > goto fail; > > > > init_one_lru(l); > > - memcg_lrus->lru[i] = l; > > + rcu_assign_pointer(memcg_lrus->lru[i], l); > > } > > return 0; > > fail: > > @@ -325,25 +339,37 @@ static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus, > > static int memcg_init_list_lru_node(struct list_lru_node *nlru) > > { > > int size = memcg_nr_cache_ids; > > + struct list_lru_memcg *tmp; > > > > - nlru->memcg_lrus = kvmalloc(size * sizeof(void *), GFP_KERNEL); > > - if (!nlru->memcg_lrus) > > + tmp = kvmalloc(size * sizeof(void *), GFP_KERNEL); > > + if (!tmp) > > return -ENOMEM; > > > > - if (__memcg_init_list_lru_node(nlru->memcg_lrus, 0, size)) { > > - kvfree(nlru->memcg_lrus); > > + if (__memcg_init_list_lru_node(tmp, 0, size)) { > > + kvfree(tmp); > > return -ENOMEM; > > } > > > > + rcu_assign_pointer(nlru->memcg_lrus, tmp); > > + > > return 0; > > } > > > > -static void memcg_destroy_list_lru_node(struct list_lru_node *nlru) > > +static void memcg_destroy_list_lru_node_rcu(struct rcu_head *rcu) > > { > > + struct list_lru_node *nlru; > > + > > + nlru = container_of(rcu, struct list_lru_node, rcu); > > + > > __memcg_destroy_list_lru_node(nlru->memcg_lrus, 0, memcg_nr_cache_ids); > > kvfree(nlru->memcg_lrus); > > } > > > > +static void memcg_destroy_list_lru_node(struct list_lru_node *nlru) > > +{ > > + call_rcu(&nlru->rcu, memcg_destroy_list_lru_node_rcu); > > +} > > + > > static int memcg_update_list_lru_node(struct list_lru_node *nlru, > > int old_size, int new_size) > > { > > @@ -371,9 +397,10 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru, > > * we have to use IRQ-safe primitives here to avoid deadlock. > > */ > > spin_lock_irq(&nlru->lock); > > - nlru->memcg_lrus = new; > > + rcu_assign_pointer(nlru->memcg_lrus, new); > > spin_unlock_irq(&nlru->lock); > > > > + synchronize_rcu(); > > kvfree(old); > > return 0; > > } > > @@ -487,6 +514,7 @@ static void memcg_drain_list_lru_node(struct list_lru_node *nlru, > > * we have to use IRQ-safe primitives here to avoid deadlock. > > */ > > spin_lock_irq(&nlru->lock); > > + rcu_read_lock(); > > > > src = list_lru_from_memcg_idx(nlru, src_idx); > > dst = list_lru_from_memcg_idx(nlru, dst_idx); > > @@ -495,6 +523,7 @@ static void memcg_drain_list_lru_node(struct list_lru_node *nlru, > > dst->nr_items += src->nr_items; > > src->nr_items = 0; > > > > + rcu_read_unlock(); > > spin_unlock_irq(&nlru->lock); > > } > > > > -- > > 2.11.0 > > -- > Michal Hocko > SUSE Labs >
