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Date: Thu, 9 Mar 2023 14:33:05 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Kirill Tkhai <tkhai@...ru>, 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
On 2023/3/9 06:13, Kirill Tkhai wrote:
> 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?
Yeah, will change to it.
>
> 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,
>
--
Thanks,
Qi
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