Re: [PATCH v3 01/21] drm/ttm: Allow TTM LRU list nodes of different types

[Matthew Brost <matthew.brost@intel.com>]

On Tue, May 21, 2024 at 09:16:19AM +0200, Thomas Hellström wrote:
> To be able to handle list unlocking while traversing the LRU
> list, we want the iterators not only to point to the next
> position of the list traversal, but to insert themselves as
> list nodes at that point to work around the fact that the
> next node might otherwise disappear from the list while
> the iterator is pointing to it.
> 
> These list nodes need to be easily distinguishable from other
> list nodes so that others traversing the list can skip
> over them.
> 
> So declare a struct ttm_lru_item, with a struct list_head member
> and a type enum. This will slightly increase the size of a
> struct ttm_resource.
> 
> Changes in previous series:
> - Update enum ttm_lru_item_type documentation.
> v3:
> - Introduce ttm_lru_first_res_or_null()
>   (Christian König, Thomas Hellström)
> 
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Cc: <dri-devel@lists.freedesktop.org>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/ttm/ttm_device.c   |  4 +-
>  drivers/gpu/drm/ttm/ttm_resource.c | 89 +++++++++++++++++++++++-------
>  include/drm/ttm/ttm_resource.h     | 54 +++++++++++++++++-
>  3 files changed, 125 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 434cf0258000..09411978a13a 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -274,14 +274,14 @@ static void ttm_device_clear_lru_dma_mappings(struct ttm_device *bdev,
>  	struct ttm_resource *res;
>  
>  	spin_lock(&bdev->lru_lock);
> -	while ((res = list_first_entry_or_null(list, typeof(*res), lru))) {
> +	while ((res = ttm_lru_first_res_or_null(list))) {
>  		struct ttm_buffer_object *bo = res->bo;
>  
>  		/* Take ref against racing releases once lru_lock is unlocked */
>  		if (!ttm_bo_get_unless_zero(bo))
>  			continue;
>  
> -		list_del_init(&res->lru);
> +		list_del_init(&bo->resource->lru.link);
>  		spin_unlock(&bdev->lru_lock);
>  
>  		if (bo->ttm)
> diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
> index 4a66b851b67d..db9a7a3717c4 100644
> --- a/drivers/gpu/drm/ttm/ttm_resource.c
> +++ b/drivers/gpu/drm/ttm/ttm_resource.c
> @@ -70,8 +70,8 @@ void ttm_lru_bulk_move_tail(struct ttm_lru_bulk_move *bulk)
>  			dma_resv_assert_held(pos->last->bo->base.resv);
>  
>  			man = ttm_manager_type(pos->first->bo->bdev, i);
> -			list_bulk_move_tail(&man->lru[j], &pos->first->lru,
> -					    &pos->last->lru);
> +			list_bulk_move_tail(&man->lru[j], &pos->first->lru.link,
> +					    &pos->last->lru.link);
>  		}
>  	}
>  }
> @@ -84,14 +84,38 @@ ttm_lru_bulk_move_pos(struct ttm_lru_bulk_move *bulk, struct ttm_resource *res)
>  	return &bulk->pos[res->mem_type][res->bo->priority];
>  }
>  
> +/* Return the previous resource on the list (skip over non-resource list items) */
> +static struct ttm_resource *ttm_lru_prev_res(struct ttm_resource *cur)
> +{
> +	struct ttm_lru_item *lru = &cur->lru;
> +
> +	do {
> +		lru = list_prev_entry(lru, link);
> +	} while (!ttm_lru_item_is_res(lru));
> +
> +	return ttm_lru_item_to_res(lru);
> +}
> +
> +/* Return the next resource on the list (skip over non-resource list items) */
> +static struct ttm_resource *ttm_lru_next_res(struct ttm_resource *cur)
> +{
> +	struct ttm_lru_item *lru = &cur->lru;
> +
> +	do {
> +		lru = list_next_entry(lru, link);
> +	} while (!ttm_lru_item_is_res(lru));
> +
> +	return ttm_lru_item_to_res(lru);
> +}
> +
>  /* Move the resource to the tail of the bulk move range */
>  static void ttm_lru_bulk_move_pos_tail(struct ttm_lru_bulk_move_pos *pos,
>  				       struct ttm_resource *res)
>  {
>  	if (pos->last != res) {
>  		if (pos->first == res)
> -			pos->first = list_next_entry(res, lru);
> -		list_move(&res->lru, &pos->last->lru);
> +			pos->first = ttm_lru_next_res(res);
> +		list_move(&res->lru.link, &pos->last->lru.link);
>  		pos->last = res;
>  	}
>  }
> @@ -122,11 +146,11 @@ static void ttm_lru_bulk_move_del(struct ttm_lru_bulk_move *bulk,
>  		pos->first = NULL;
>  		pos->last = NULL;
>  	} else if (pos->first == res) {
> -		pos->first = list_next_entry(res, lru);
> +		pos->first = ttm_lru_next_res(res);
>  	} else if (pos->last == res) {
> -		pos->last = list_prev_entry(res, lru);
> +		pos->last = ttm_lru_prev_res(res);
>  	} else {
> -		list_move(&res->lru, &pos->last->lru);
> +		list_move(&res->lru.link, &pos->last->lru.link);
>  	}
>  }
>  
> @@ -155,7 +179,7 @@ void ttm_resource_move_to_lru_tail(struct ttm_resource *res)
>  	lockdep_assert_held(&bo->bdev->lru_lock);
>  
>  	if (bo->pin_count) {
> -		list_move_tail(&res->lru, &bdev->pinned);
> +		list_move_tail(&res->lru.link, &bdev->pinned);
>  
>  	} else	if (bo->bulk_move) {
>  		struct ttm_lru_bulk_move_pos *pos =
> @@ -166,7 +190,7 @@ void ttm_resource_move_to_lru_tail(struct ttm_resource *res)
>  		struct ttm_resource_manager *man;
>  
>  		man = ttm_manager_type(bdev, res->mem_type);
> -		list_move_tail(&res->lru, &man->lru[bo->priority]);
> +		list_move_tail(&res->lru.link, &man->lru[bo->priority]);
>  	}
>  }
>  
> @@ -197,9 +221,9 @@ void ttm_resource_init(struct ttm_buffer_object *bo,
>  	man = ttm_manager_type(bo->bdev, place->mem_type);
>  	spin_lock(&bo->bdev->lru_lock);
>  	if (bo->pin_count)
> -		list_add_tail(&res->lru, &bo->bdev->pinned);
> +		list_add_tail(&res->lru.link, &bo->bdev->pinned);
>  	else
> -		list_add_tail(&res->lru, &man->lru[bo->priority]);
> +		list_add_tail(&res->lru.link, &man->lru[bo->priority]);
>  	man->usage += res->size;
>  	spin_unlock(&bo->bdev->lru_lock);
>  }
> @@ -221,7 +245,7 @@ void ttm_resource_fini(struct ttm_resource_manager *man,
>  	struct ttm_device *bdev = man->bdev;
>  
>  	spin_lock(&bdev->lru_lock);
> -	list_del_init(&res->lru);
> +	list_del_init(&res->lru.link);
>  	man->usage -= res->size;
>  	spin_unlock(&bdev->lru_lock);
>  }
> @@ -472,14 +496,16 @@ struct ttm_resource *
>  ttm_resource_manager_first(struct ttm_resource_manager *man,
>  			   struct ttm_resource_cursor *cursor)
>  {
> -	struct ttm_resource *res;
> +	struct ttm_lru_item *lru;
>  
>  	lockdep_assert_held(&man->bdev->lru_lock);
>  
>  	for (cursor->priority = 0; cursor->priority < TTM_MAX_BO_PRIORITY;
>  	     ++cursor->priority)
> -		list_for_each_entry(res, &man->lru[cursor->priority], lru)
> -			return res;
> +		list_for_each_entry(lru, &man->lru[cursor->priority], link) {
> +			if (ttm_lru_item_is_res(lru))
> +				return ttm_lru_item_to_res(lru);
> +		}
>  
>  	return NULL;
>  }
> @@ -498,15 +524,40 @@ ttm_resource_manager_next(struct ttm_resource_manager *man,
>  			  struct ttm_resource_cursor *cursor,
>  			  struct ttm_resource *res)
>  {
> +	struct ttm_lru_item *lru = &res->lru;
> +
>  	lockdep_assert_held(&man->bdev->lru_lock);
>  
> -	list_for_each_entry_continue(res, &man->lru[cursor->priority], lru)
> -		return res;
> +	list_for_each_entry_continue(lru, &man->lru[cursor->priority], link) {
> +		if (ttm_lru_item_is_res(lru))
> +			return ttm_lru_item_to_res(lru);
> +	}
>  
>  	for (++cursor->priority; cursor->priority < TTM_MAX_BO_PRIORITY;
>  	     ++cursor->priority)
> -		list_for_each_entry(res, &man->lru[cursor->priority], lru)
> -			return res;
> +		list_for_each_entry(lru, &man->lru[cursor->priority], link) {
> +			if (ttm_lru_item_is_res(lru))
> +				ttm_lru_item_to_res(lru);
> +		}
> +
> +	return NULL;
> +}
> +
> +/**
> + * ttm_lru_first_res_or_null() - Return the first resource on an lru list
> + * @head: The list head of the lru list.
> + *
> + * Return: Pointer to the first resource on the lru list or NULL if
> + * there is none.
> + */
> +struct ttm_resource *ttm_lru_first_res_or_null(struct list_head *head)
> +{
> +	struct ttm_lru_item *lru;
> +
> +	list_for_each_entry(lru, head, link) {
> +		if (ttm_lru_item_is_res(lru))
> +			return ttm_lru_item_to_res(lru);
> +	}
>  
>  	return NULL;
>  }
> diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
> index 69769355139f..1511d91e290d 100644
> --- a/include/drm/ttm/ttm_resource.h
> +++ b/include/drm/ttm/ttm_resource.h
> @@ -49,6 +49,43 @@ struct io_mapping;
>  struct sg_table;
>  struct scatterlist;
>  
> +/**
> + * enum ttm_lru_item_type - enumerate ttm_lru_item subclasses
> + */
> +enum ttm_lru_item_type {
> +	/** @TTM_LRU_RESOURCE: The resource subclass */
> +	TTM_LRU_RESOURCE,
> +	/** @TTM_LRU_HITCH: The iterator hitch subclass */
> +	TTM_LRU_HITCH
> +};
> +
> +/**
> + * struct ttm_lru_item - The TTM lru list node base class
> + * @link: The list link
> + * @type: The subclass type
> + */
> +struct ttm_lru_item {
> +	struct list_head link;
> +	enum ttm_lru_item_type type;
> +};
> +
> +/**
> + * ttm_lru_item_init() - initialize a struct ttm_lru_item
> + * @item: The item to initialize
> + * @type: The subclass type
> + */
> +static inline void ttm_lru_item_init(struct ttm_lru_item *item,
> +				     enum ttm_lru_item_type type)
> +{
> +	item->type = type;
> +	INIT_LIST_HEAD(&item->link);
> +}
> +
> +static inline bool ttm_lru_item_is_res(const struct ttm_lru_item *item)
> +{
> +	return item->type == TTM_LRU_RESOURCE;
> +}
> +
>  struct ttm_resource_manager_func {
>  	/**
>  	 * struct ttm_resource_manager_func member alloc
> @@ -217,9 +254,21 @@ struct ttm_resource {
>  	/**
>  	 * @lru: Least recently used list, see &ttm_resource_manager.lru
>  	 */
> -	struct list_head lru;
> +	struct ttm_lru_item lru;
>  };
>  
> +/**
> + * ttm_lru_item_to_res() - Downcast a struct ttm_lru_item to a struct ttm_resource
> + * @item: The struct ttm_lru_item to downcast
> + *
> + * Return: Pointer to the embedding struct ttm_resource
> + */
> +static inline struct ttm_resource *
> +ttm_lru_item_to_res(struct ttm_lru_item *item)
> +{
> +	return container_of(item, struct ttm_resource, lru);
> +}
> +
>  /**
>   * struct ttm_resource_cursor
>   *
> @@ -393,6 +442,9 @@ ttm_resource_manager_next(struct ttm_resource_manager *man,
>  			  struct ttm_resource_cursor *cursor,
>  			  struct ttm_resource *res);
>  
> +struct ttm_resource *
> +ttm_lru_first_res_or_null(struct list_head *head);
> +
>  /**
>   * ttm_resource_manager_for_each_res - iterate over all resources
>   * @man: the resource manager
> -- 
> 2.44.0
>