Re: [PATCH RFC 2/6] mm, slab: always maintain per-node slab and object count

[Vlastimil Babka]

On 7/22/24 4:16 PM, Xiongwei Song wrote:
> Don't we need the following changes for this patch?

Yes thanks, will fix!

> diff --git a/mm/slub.c b/mm/slub.c
> index c1222467c346..e6beb6743342 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4967,9 +4967,9 @@ init_kmem_cache_node(struct kmem_cache_node *n)
>         n->nr_partial = 0;
>         spin_lock_init(&n->list_lock);
>         INIT_LIST_HEAD(&n->partial);
> -#ifdef CONFIG_SLUB_DEBUG
>         atomic_long_set(&n->nr_slabs, 0);
>         atomic_long_set(&n->total_objects, 0);
> +#ifdef CONFIG_SLUB_DEBUG
>         INIT_LIST_HEAD(&n->full);
>  #endif
>  }
> 
> Thanks,
> Xiongwei
> 
> 
> On Tue, Jul 16, 2024 at 4:29 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>>
>> Currently SLUB counts per-node slabs and total objects only with
>> CONFIG_SLUB_DEBUG, in order to minimize overhead. However, the detection
>> in __kmem_cache_shutdown() whether there are no outstanding object
>> relies on the per-node slab count (node_nr_slabs()) so it may be
>> unreliable without CONFIG_SLUB_DEBUG. Thus we might be failing to warn
>> about such situations, and instead destroy a cache while leaving its
>> slab(s) around (due to a buggy slab user creating such a scenario, not
>> in normal operation).
>>
>> We will also need node_nr_slabs() to be reliable in the following work
>> to gracefully handle kmem_cache_destroy() with kfree_rcu() objects in
>> flight. Thus make the counting of per-node slabs and objects
>> unconditional.
>>
>> Note that CONFIG_SLUB_DEBUG is the default anyway, and the counting is
>> done only when allocating or freeing a slab page, so even in
>> !CONFIG_SLUB_DEBUG configs the overhead should be negligible.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>> ---
>>  mm/slub.c | 49 +++++++++++++++++++++----------------------------
>>  1 file changed, 21 insertions(+), 28 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 829a1f08e8a2..aa4d80109c49 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -426,9 +426,9 @@ struct kmem_cache_node {
>>         spinlock_t list_lock;
>>         unsigned long nr_partial;
>>         struct list_head partial;
>> -#ifdef CONFIG_SLUB_DEBUG
>>         atomic_long_t nr_slabs;
>>         atomic_long_t total_objects;
>> +#ifdef CONFIG_SLUB_DEBUG
>>         struct list_head full;
>>  #endif
>>  };
>> @@ -438,6 +438,26 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
>>         return s->node[node];
>>  }
>>
>> +static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
>> +{
>> +       return atomic_long_read(&n->nr_slabs);
>> +}
>> +
>> +static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects)
>> +{
>> +       struct kmem_cache_node *n = get_node(s, node);
>> +
>> +       atomic_long_inc(&n->nr_slabs);
>> +       atomic_long_add(objects, &n->total_objects);
>> +}
>> +static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects)
>> +{
>> +       struct kmem_cache_node *n = get_node(s, node);
>> +
>> +       atomic_long_dec(&n->nr_slabs);
>> +       atomic_long_sub(objects, &n->total_objects);
>> +}
>> +
>>  /*
>>   * Iterator over all nodes. The body will be executed for each node that has
>>   * a kmem_cache_node structure allocated (which is true for all online nodes)
>> @@ -1511,26 +1531,6 @@ static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct
>>         list_del(&slab->slab_list);
>>  }
>>
>> -static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
>> -{
>> -       return atomic_long_read(&n->nr_slabs);
>> -}
>> -
>> -static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects)
>> -{
>> -       struct kmem_cache_node *n = get_node(s, node);
>> -
>> -       atomic_long_inc(&n->nr_slabs);
>> -       atomic_long_add(objects, &n->total_objects);
>> -}
>> -static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects)
>> -{
>> -       struct kmem_cache_node *n = get_node(s, node);
>> -
>> -       atomic_long_dec(&n->nr_slabs);
>> -       atomic_long_sub(objects, &n->total_objects);
>> -}
>> -
>>  /* Object debug checks for alloc/free paths */
>>  static void setup_object_debug(struct kmem_cache *s, void *object)
>>  {
>> @@ -1871,13 +1871,6 @@ slab_flags_t kmem_cache_flags(slab_flags_t flags, const char *name)
>>
>>  #define disable_higher_order_debug 0
>>
>> -static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
>> -                                                       { return 0; }
>> -static inline void inc_slabs_node(struct kmem_cache *s, int node,
>> -                                                       int objects) {}
>> -static inline void dec_slabs_node(struct kmem_cache *s, int node,
>> -                                                       int objects) {}
>> -
>>  #ifndef CONFIG_SLUB_TINY
>>  static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
>>                                void **freelist, void *nextfree)
>>
>> --
>> 2.45.2
>>
>>
>