Re: [patch 15/25] debugobjects: Rework object allocation

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

On 2024/10/8 0:50, Thomas Gleixner wrote:
> The current allocation scheme tries to allocate from the per CPU pool
> first. If that fails it allocates one object from the global pool and then
> refills the per CPU pool from the global pool.
> 
> That is in the way of switching the pool management to batch mode as the
> global pool needs to be a strict stack of batches, which does not allow
> to allocate single objects.
> 
> Rework the code to refill the per CPU pool first and then allocate the
> object from the refilled batch. Also try to allocate from the to free pool
> first to avoid freeing and reallocating objects.

Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>

> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  lib/debugobjects.c |  144 +++++++++++++++++++++++++----------------------------
>  1 file changed, 69 insertions(+), 75 deletions(-)
> 
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -141,6 +141,64 @@ static __always_inline bool pool_must_re
>  	return pool_count(pool) < pool->min_cnt / 2;
>  }
>  
> +static bool pool_move_batch(struct obj_pool *dst, struct obj_pool *src)
> +{
> +	if (dst->cnt + ODEBUG_BATCH_SIZE > dst->max_cnt || !src->cnt)
> +		return false;
> +
> +	for (int i = 0; i < ODEBUG_BATCH_SIZE && src->cnt; i++) {
> +		struct hlist_node *node = src->objects.first;
> +
> +		WRITE_ONCE(src->cnt, src->cnt - 1);
> +		WRITE_ONCE(dst->cnt, dst->cnt + 1);
> +
> +		hlist_del(node);
> +		hlist_add_head(node, &dst->objects);
> +	}
> +	return true;
> +}
> +
> +static struct debug_obj *__alloc_object(struct hlist_head *list)
> +{
> +	struct debug_obj *obj;
> +
> +	if (unlikely(!list->first))
> +		return NULL;
> +
> +	obj = hlist_entry(list->first, typeof(*obj), node);
> +	hlist_del(&obj->node);
> +	return obj;
> +}
> +
> +static struct debug_obj *pcpu_alloc(void)
> +{
> +	struct obj_pool *pcp = this_cpu_ptr(&pool_pcpu);
> +
> +	lockdep_assert_irqs_disabled();
> +
> +	for (;;) {
> +		struct debug_obj *obj = __alloc_object(&pcp->objects);
> +
> +		if (likely(obj)) {
> +			pcp->cnt--;
> +			return obj;
> +		}
> +
> +		guard(raw_spinlock)(&pool_lock);
> +		if (!pool_move_batch(pcp, &pool_to_free)) {
> +			if (!pool_move_batch(pcp, &pool_global))
> +				return NULL;
> +		}
> +		obj_pool_used += pcp->cnt;
> +
> +		if (obj_pool_used > obj_pool_max_used)
> +			obj_pool_max_used = obj_pool_used;
> +
> +		if (pool_global.cnt < obj_pool_min_free)
> +			obj_pool_min_free = pool_global.cnt;
> +	}
> +}
> +
>  static void free_object_list(struct hlist_head *head)
>  {
>  	struct hlist_node *tmp;
> @@ -158,7 +216,6 @@ static void free_object_list(struct hlis
>  static void fill_pool_from_freelist(void)
>  {
>  	static unsigned long state;
> -	struct debug_obj *obj;
>  
>  	/*
>  	 * Reuse objs from the global obj_to_free list; they will be
> @@ -180,17 +237,11 @@ static void fill_pool_from_freelist(void
>  	if (test_bit(0, &state) || test_and_set_bit(0, &state))
>  		return;
>  
> -	guard(raw_spinlock)(&pool_lock);
> -	/*
> -	 * Recheck with the lock held as the worker thread might have
> -	 * won the race and freed the global free list already.
> -	 */
> -	while (pool_to_free.cnt && (pool_global.cnt < pool_global.min_cnt)) {
> -		obj = hlist_entry(pool_to_free.objects.first, typeof(*obj), node);
> -		hlist_del(&obj->node);
> -		WRITE_ONCE(pool_to_free.cnt, pool_to_free.cnt - 1);
> -		hlist_add_head(&obj->node, &pool_global.objects);
> -		WRITE_ONCE(pool_global.cnt, pool_global.cnt + 1);
> +	/* Avoid taking the lock when there is no work to do */
> +	while (pool_should_refill(&pool_global) && pool_count(&pool_to_free)) {
> +		guard(raw_spinlock)(&pool_lock);
> +		/* Move a batch if possible */
> +		pool_move_batch(&pool_global, &pool_to_free);
>  	}
>  	clear_bit(0, &state);
>  }
> @@ -251,74 +302,17 @@ static struct debug_obj *lookup_object(v
>  	return NULL;
>  }
>  
> -/*
> - * Allocate a new object from the hlist
> - */
> -static struct debug_obj *__alloc_object(struct hlist_head *list)
> +static struct debug_obj *alloc_object(void *addr, struct debug_bucket *b,
> +				      const struct debug_obj_descr *descr)
>  {
> -	struct debug_obj *obj = NULL;
> -
> -	if (list->first) {
> -		obj = hlist_entry(list->first, typeof(*obj), node);
> -		hlist_del(&obj->node);
> -	}
> -
> -	return obj;
> -}
> -
> -static struct debug_obj *
> -alloc_object(void *addr, struct debug_bucket *b, const struct debug_obj_descr *descr)
> -{
> -	struct obj_pool *percpu_pool = this_cpu_ptr(&pool_pcpu);
>  	struct debug_obj *obj;
>  
> -	if (likely(obj_cache)) {
> -		obj = __alloc_object(&percpu_pool->objects);
> -		if (obj) {
> -			percpu_pool->cnt--;
> -			goto init_obj;
> -		}
> -	} else {
> +	if (likely(obj_cache))
> +		obj = pcpu_alloc();
> +	else
>  		obj = __alloc_object(&pool_boot);
> -		goto init_obj;
> -	}
> -
> -	raw_spin_lock(&pool_lock);
> -	obj = __alloc_object(&pool_global.objects);
> -	if (obj) {
> -		obj_pool_used++;
> -		WRITE_ONCE(pool_global.cnt, pool_global.cnt - 1);
> -
> -		/*
> -		 * Looking ahead, allocate one batch of debug objects and
> -		 * put them into the percpu free pool.
> -		 */
> -		if (likely(obj_cache)) {
> -			int i;
> -
> -			for (i = 0; i < ODEBUG_BATCH_SIZE; i++) {
> -				struct debug_obj *obj2;
> -
> -				obj2 = __alloc_object(&pool_global.objects);
> -				if (!obj2)
> -					break;
> -				hlist_add_head(&obj2->node, &percpu_pool->objects);
> -				percpu_pool->cnt++;
> -				obj_pool_used++;
> -				WRITE_ONCE(pool_global.cnt, pool_global.cnt - 1);
> -			}
> -		}
> -
> -		if (obj_pool_used > obj_pool_max_used)
> -			obj_pool_max_used = obj_pool_used;
> -
> -		if (pool_global.cnt < obj_pool_min_free)
> -			obj_pool_min_free = pool_global.cnt;
> -	}
> -	raw_spin_unlock(&pool_lock);
>  
> -init_obj:
> -	if (obj) {
> +	if (likely(obj)) {
>  		obj->object = addr;
>  		obj->descr  = descr;
>  		obj->state  = ODEBUG_STATE_NONE;
> 
> .
> 

-- 
Regards,
  Zhen Lei