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Message-ID: <eab519de-1222-b097-9eb4-28a444458c28@ya.ru>
Date: Thu, 9 Mar 2023 01:13:46 +0300
From: Kirill Tkhai <tkhai@...ru>
To: Qi Zheng <zhengqi.arch@...edance.com>, akpm@...ux-foundation.org,
hannes@...xchg.org, shakeelb@...gle.com, mhocko@...nel.org,
roman.gushchin@...ux.dev, muchun.song@...ux.dev, david@...hat.com,
shy828301@...il.com, rppt@...nel.org
Cc: sultan@...neltoast.com, dave@...olabs.net,
penguin-kernel@...ove.SAKURA.ne.jp, paulmck@...nel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/8] mm: vmscan: add a map_nr_max field to
shrinker_info
Hi,
On 07.03.2023 09:55, Qi Zheng wrote:
> To prepare for the subsequent lockless memcg slab shrink,
> add a map_nr_max field to struct shrinker_info to records
> its own real shrinker_nr_max.
>
> Suggested-by: Kirill Tkhai <tkhai@...ru>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
> include/linux/memcontrol.h | 1 +
> mm/vmscan.c | 41 ++++++++++++++++++++++----------------
> 2 files changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index b6eda2ab205d..aa69ea98e2d8 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -97,6 +97,7 @@ struct shrinker_info {
> struct rcu_head rcu;
> atomic_long_t *nr_deferred;
> unsigned long *map;
> + int map_nr_max;
> };
>
> struct lruvec_stats_percpu {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9414226218f0..2dcc01682026 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -224,9 +224,16 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
> lockdep_is_held(&shrinker_rwsem));
> }
>
> +static inline bool need_expand(int new_nr_max, int old_nr_max)
> +{
> + return round_up(new_nr_max, BITS_PER_LONG) >
> + round_up(old_nr_max, BITS_PER_LONG);
> +}
> +
> static int expand_one_shrinker_info(struct mem_cgroup *memcg,
> int map_size, int defer_size,
> - int old_map_size, int old_defer_size)
> + int old_map_size, int old_defer_size,
> + int new_nr_max)
> {
> struct shrinker_info *new, *old;
> struct mem_cgroup_per_node *pn;
> @@ -240,12 +247,17 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
> if (!old)
> return 0;
>
> + /* Already expanded this shrinker_info */
> + if (!need_expand(new_nr_max, old->map_nr_max))
need_expand() looks confusing here. It's strange that we round_up(old->map_nr_max),
despite old->map never may exceed old->map_nr_max.
Won't plain
if (new_nr_max <= old->map_nr_max)
look clearer here?
The rest in patch looks OK for me.
> + continue;
> +
> new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
> if (!new)
> return -ENOMEM;
>
> new->nr_deferred = (atomic_long_t *)(new + 1);
> new->map = (void *)new->nr_deferred + defer_size;
> + new->map_nr_max = new_nr_max;
>
> /* map: set all old bits, clear all new bits */
> memset(new->map, (int)0xff, old_map_size);
> @@ -295,6 +307,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
> }
> info->nr_deferred = (atomic_long_t *)(info + 1);
> info->map = (void *)info->nr_deferred + defer_size;
> + info->map_nr_max = shrinker_nr_max;
> rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
> }
> up_write(&shrinker_rwsem);
> @@ -302,23 +315,14 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
> return ret;
> }
>
> -static inline bool need_expand(int nr_max)
> -{
> - return round_up(nr_max, BITS_PER_LONG) >
> - round_up(shrinker_nr_max, BITS_PER_LONG);
> -}
> -
> static int expand_shrinker_info(int new_id)
> {
> int ret = 0;
> - int new_nr_max = new_id + 1;
> + int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
> int map_size, defer_size = 0;
> int old_map_size, old_defer_size = 0;
> struct mem_cgroup *memcg;
>
> - if (!need_expand(new_nr_max))
> - goto out;
> -
> if (!root_mem_cgroup)
> goto out;
>
> @@ -332,7 +336,8 @@ static int expand_shrinker_info(int new_id)
> memcg = mem_cgroup_iter(NULL, NULL, NULL);
> do {
> ret = expand_one_shrinker_info(memcg, map_size, defer_size,
> - old_map_size, old_defer_size);
> + old_map_size, old_defer_size,
> + new_nr_max);
> if (ret) {
> mem_cgroup_iter_break(NULL, memcg);
> goto out;
> @@ -352,9 +357,11 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
>
> rcu_read_lock();
> info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
> - /* Pairs with smp mb in shrink_slab() */
> - smp_mb__before_atomic();
> - set_bit(shrinker_id, info->map);
> + if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
> + /* Pairs with smp mb in shrink_slab() */
> + smp_mb__before_atomic();
> + set_bit(shrinker_id, info->map);
> + }
> rcu_read_unlock();
> }
> }
> @@ -432,7 +439,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
> for_each_node(nid) {
> child_info = shrinker_info_protected(memcg, nid);
> parent_info = shrinker_info_protected(parent, nid);
> - for (i = 0; i < shrinker_nr_max; i++) {
> + for (i = 0; i < child_info->map_nr_max; i++) {
> nr = atomic_long_read(&child_info->nr_deferred[i]);
> atomic_long_add(nr, &parent_info->nr_deferred[i]);
> }
> @@ -899,7 +906,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> if (unlikely(!info))
> goto unlock;
>
> - for_each_set_bit(i, info->map, shrinker_nr_max) {
> + for_each_set_bit(i, info->map, info->map_nr_max) {
> struct shrink_control sc = {
> .gfp_mask = gfp_mask,
> .nid = nid,
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