lkml.org 
[lkml]   [2023]   [Feb]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2 1/7] mm: vmscan: add a map_nr_max field to shrinker_info
From


On 2023/2/25 23:14, Kirill Tkhai wrote:
> Hi Qi,
>
> On 25.02.2023 11:18, Qi Zheng wrote:
>>
>>
>> On 2023/2/23 21:27, 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.
>>>
>>> No functional changes.
>>>
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> I missed Suggested-by here, hi Kirill, can I add it?
>>
>> Suggested-by: Kirill Tkhai <tkhai@ya.ru>
>
> Yes, feel free to add this tag.
>
> There is a comment below.
>
>>> ---
>>>   include/linux/memcontrol.h |  1 +
>>>   mm/vmscan.c                | 29 ++++++++++++++++++-----------
>>>   2 files changed, 19 insertions(+), 11 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 9c1c5e8b24b8..9f895ca6216c 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 +247,16 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>>>           if (!old)
>>>               return 0;
>>>   +        if (!need_expand(new_nr_max, old->map_nr_max))
>>> +            return 0;
>>> +
>>>           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 +306,7 @@ 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);
>>> @@ -302,12 +314,6 @@ 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;
>>> @@ -316,7 +322,7 @@ static int expand_shrinker_info(int new_id)
>>>       int old_map_size, old_defer_size = 0;
>>>       struct mem_cgroup *memcg;
>>>   -    if (!need_expand(new_nr_max))
>>> +    if (!need_expand(new_nr_max, shrinker_nr_max))
>>>           goto out;
>>>         if (!root_mem_cgroup)
>>> @@ -332,7 +338,8 @@ 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;
>>> @@ -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,
>
> The patch as whole thing won't work as expected. It won't ever call shrinker with ids from [round_down(shrinker_nr_max, sizeof(unsigned long)) + 1, shrinker_nr_max - 1]
>
> Just replay the sequence we add new shrinkers:
>
> 1)We add shrinker #0:
> shrinker_nr_max = 0;
>
> prealloc_memcg_shrinker()
> id = 0;
> expand_shrinker_info(0)
> new_nr_max = 1;
> expand_one_shrinker_info(new_nr_max = 1)
> new->map_nr_max = 1;
> shrinker_nr_max = 1;
>
> 2)We add shrinker #1:
> prealloc_memcg_shrinker()
> id = 1;
> expand_shrinker_info(1)
> new_nr_max = 2;
> need_expand(2, 1) => false => ignore expand
> shrinker_nr_max = 2;
>
> 3)Then we call shrinker:
> shrink_slab_memcg()
> for_each_set_bit(i, info->map, 1/* info->map_nr_max */ ) {
> } => ignore shrinker #1
>
> I'd fixed this patch by something like the below:
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9f895ca6216c..bb617a3871f1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -224,12 +224,6 @@ 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,
> @@ -247,9 +241,6 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
> if (!old)
> return 0;
>
> - if (!need_expand(new_nr_max, old->map_nr_max))
> - return 0;
> -

Maybe we can keep this. For example, when we failed to allocate memory
by calling kvmalloc_node() last time, some shrinker_info may have been
expanded, and these shrinker_info do not need to be expanded again.

> new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
> if (!new)
> return -ENOMEM;
> @@ -317,14 +308,11 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
> 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, shrinker_nr_max))
> - goto out;
> -
> if (!root_mem_cgroup)
> goto out;
>
> @@ -359,9 +347,11 @@ 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();
> }
> }
>
> (I also added a new check into set_shrinker_bit() for safety).
>
> Kirill

--
Thanks,
Qi

\
 
 \ /
  Last update: 2023-03-27 00:35    [W:0.169 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site