Re: [patch 20/25] debugobjects: Prepare kmem_cache allocations for batching

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2024/10/8 0:50, Thomas Gleixner wrote:
> Allocate a batch and then push it into the pool. Utilize the
> debug_obj::last_node pointer for keeping track of the batch boundary.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  lib/debugobjects.c |   80 ++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 49 insertions(+), 31 deletions(-)
> 
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -164,6 +164,22 @@ static bool pool_move_batch(struct obj_p
>  	return true;
>  }
>  
> +static bool pool_push_batch(struct obj_pool *dst, struct hlist_head *head)
> +{
> +	struct hlist_node *last;
> +	struct debug_obj *obj;
> +
> +	if (dst->cnt >= dst->max_cnt)
> +		return false;
> +
> +	obj = hlist_entry(head->first, typeof(*obj), node);
> +	last = obj->batch_last;
> +
> +	hlist_splice_init(head, last, &dst->objects);
> +	WRITE_ONCE(dst->cnt, dst->cnt + ODEBUG_BATCH_SIZE);
> +	return true;
> +}
> +
>  static bool pool_pop_batch(struct hlist_head *head, struct obj_pool *src)
>  {
>  	if (!src->cnt)
> @@ -288,6 +304,28 @@ static void fill_pool_from_freelist(void
>  	clear_bit(0, &state);
>  }
>  
> +static bool kmem_alloc_batch(struct hlist_head *head, struct kmem_cache *cache, gfp_t gfp)
> +{
> +	struct hlist_node *last = NULL;
> +	struct debug_obj *obj;
> +
> +	for (int cnt = 0; cnt < ODEBUG_BATCH_SIZE; cnt++) {
> +		obj = kmem_cache_zalloc(cache, gfp);
> +		if (!obj) {
> +			free_object_list(head);
> +			return false;
> +		}
> +		debug_objects_allocated++;
> +
> +		if (!last)
> +			last = &obj->node;
> +		obj->batch_last = last;
> +
> +		hlist_add_head(&obj->node, head);

There seems to be a need to use hlist_splice_init() outside the loop like patch 2/25.
Prepare the local list first, if all ODEBUG_BATCH_SIZE is successfully allocated,
attach it to 'head' at a time, including account debug_objects_allocated. Then back
to patch 8/25, keep debug_objects_freed still in lock protection and do not move it
into free_object_list(). Seems like it should be.

> +	}
> +	return true;
> +}
> +
>  static void fill_pool(void)
>  {
>  	static atomic_t cpus_allocating;
> @@ -302,25 +340,14 @@ static void fill_pool(void)
>  
>  	atomic_inc(&cpus_allocating);
>  	while (pool_should_refill(&pool_global)) {
> -		struct debug_obj *new, *last = NULL;
>  		HLIST_HEAD(head);
> -		int cnt;
>  
> -		for (cnt = 0; cnt < ODEBUG_BATCH_SIZE; cnt++) {
> -			new = kmem_cache_zalloc(obj_cache, __GFP_HIGH | __GFP_NOWARN);
> -			if (!new)
> -				break;
> -			hlist_add_head(&new->node, &head);
> -			if (!last)
> -				last = new;
> -		}
> -		if (!cnt)
> +		if (!kmem_alloc_batch(&head, obj_cache, __GFP_HIGH | __GFP_NOWARN))
>  			break;
>  
>  		guard(raw_spinlock_irqsave)(&pool_lock);
> -		hlist_splice_init(&head, &last->node, &pool_global.objects);
> -		debug_objects_allocated += cnt;
> -		WRITE_ONCE(pool_global.cnt, pool_global.cnt + cnt);
> +		if (!pool_push_batch(&pool_global, &head))
> +			pool_push_batch(&pool_to_free, &head);
>  	}
>  	atomic_dec(&cpus_allocating);
>  }
> @@ -1302,26 +1329,18 @@ void __init debug_objects_early_init(voi
>  static bool __init debug_objects_replace_static_objects(struct kmem_cache *cache)
>  {
>  	struct debug_bucket *db = obj_hash;
> -	struct debug_obj *obj, *new;
>  	struct hlist_node *tmp;
> +	struct debug_obj *obj;
>  	HLIST_HEAD(objects);
>  	int i;
>  
> -	for (i = 0; i < ODEBUG_POOL_SIZE; i++) {
> -		obj = kmem_cache_zalloc(cache, GFP_KERNEL);
> -		if (!obj)
> +	for (i = 0; i < ODEBUG_POOL_SIZE; i += ODEBUG_BATCH_SIZE) {
> +		if (!kmem_alloc_batch(&objects, cache, GFP_KERNEL))
>  			goto free;
> -		hlist_add_head(&obj->node, &objects);
> +		pool_push_batch(&pool_global, &objects);
>  	}
>  
> -	debug_objects_allocated = ODEBUG_POOL_SIZE;
> -	pool_global.cnt = ODEBUG_POOL_SIZE;
> -
> -	/*
> -	 * Move the allocated objects to the global pool and disconnect the
> -	 * boot pool.
> -	 */
> -	hlist_move_list(&objects, &pool_global.objects);
> +	/* Disconnect the boot pool. */
>  	pool_boot.first = NULL;
>  
>  	/* Replace the active object references */
> @@ -1329,9 +1348,8 @@ static bool __init debug_objects_replace
>  		hlist_move_list(&db->list, &objects);
>  
>  		hlist_for_each_entry(obj, &objects, node) {
> -			new = hlist_entry(pool_global.objects.first, typeof(*obj), node);
> -			hlist_del(&new->node);
> -			pool_global.cnt--;
> +			struct debug_obj *new = pcpu_alloc();
> +
>  			/* copy object data */
>  			*new = *obj;
>  			hlist_add_head(&new->node, &db->list);
> @@ -1340,7 +1358,7 @@ static bool __init debug_objects_replace
>  	return true;
>  free:
>  	/* Can't use free_object_list() as the cache is not populated yet */
> -	hlist_for_each_entry_safe(obj, tmp, &objects, node) {
> +	hlist_for_each_entry_safe(obj, tmp, &pool_global.objects, node) {
>  		hlist_del(&obj->node);
>  		kmem_cache_free(cache, obj);
>  	}
> 
> .
> 

-- 
Regards,
  Zhen Lei