On Tue, Apr 16, 2024 at 12:07:22PM +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.
>
Patch itself makes sense to me. One style question (or maybe
suggestion?) below.
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: Somalapuram Amaranath <Amaranath.Somalapuram@xxxxxxx>
> Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/ttm/ttm_device.c | 13 ++++--
> drivers/gpu/drm/ttm/ttm_resource.c | 70 ++++++++++++++++++++++--------
> include/drm/ttm/ttm_resource.h | 51 +++++++++++++++++++++-
> 3 files changed, 110 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 76027960054f..f27406e851e5 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -270,17 +270,22 @@ EXPORT_SYMBOL(ttm_device_fini);
> static void ttm_device_clear_lru_dma_mappings(struct ttm_device *bdev,
> struct list_head *list)
> {
> - struct ttm_resource *res;
> + struct ttm_lru_item *lru;
>
> spin_lock(&bdev->lru_lock);
> - while ((res = list_first_entry_or_null(list, typeof(*res), lru))) {
> - struct ttm_buffer_object *bo = res->bo;
> + while ((lru = list_first_entry_or_null(list, typeof(*lru), link))) {
> + struct ttm_buffer_object *bo;
> +
> + if (!ttm_lru_item_is_res(lru))
> + continue;
> +
> + bo = ttm_lru_item_to_res(lru)->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 be8d286513f9..7aa5ca5c0e33 100644
> --- a/drivers/gpu/drm/ttm/ttm_resource.c
> +++ b/drivers/gpu/drm/ttm/ttm_resource.c
> @@ -69,8 +69,8 @@ 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);
> }
> }
> }
> @@ -83,14 +83,38 @@ 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;
> }
> }
> @@ -121,11 +145,11 @@ 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);
> }
> }
>
> @@ -154,7 +178,7 @@ 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 =
> @@ -165,7 +189,7 @@ 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]);
> }
> }
>
> @@ -196,9 +220,9 @@ 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);
> }
> @@ -220,7 +244,7 @@ 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);
> }
> @@ -471,14 +495,16 @@ 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;
> }
> @@ -497,15 +523,21 @@ 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;
> }
> diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
> index 69769355139f..4babc4ff10b0 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)
Pretty much everywhere in this series we have the following coding
pattern:
if (ttm_lru_item_is_res(item))
do something with ttm_lru_item_to_res(item);
Would it make more sense to squash these functions together with only
ttm_lru_item_to_res which returns NULL if item is not TTM_LRU_RESOURCE?
The new pattern would be:
res = ttm_lru_item_is_res(item)
if (res)
do something with res
What do you think?
Matt
> +{
> + return container_of(item, struct ttm_resource, lru);
> +}
> +
> /**
> * struct ttm_resource_cursor
> *
> --
> 2.44.0
>
