Re: [PATCH 1/2] drm/mm: Add an iterator to optimally walk over holes for an allocation

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 02/02/2022 01:13, Vivek Kasireddy wrote:
> This iterator relies on drm_mm_first_hole() and drm_mm_next_hole()
> functions to identify suitable holes for an allocation of a given
> size by efficently traversing the rbtree associated with the given
> allocator.
> 
> It replaces the for loop in drm_mm_insert_node_in_range() and can
> also be used by drm drivers to quickly identify holes of a certain
> size within a given range.
> 
> Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>   drivers/gpu/drm/drm_mm.c | 28 ++++++++++++----------------
>   include/drm/drm_mm.h     | 32 ++++++++++++++++++++++++++++++++
>   2 files changed, 44 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> index 8257f9d4f619..416c849c10e5 100644
> --- a/drivers/gpu/drm/drm_mm.c
> +++ b/drivers/gpu/drm/drm_mm.c
> @@ -352,10 +352,10 @@ static struct drm_mm_node *find_hole_addr(struct drm_mm *mm, u64 addr, u64 size)
>   	return node;
>   }
>   
> -static struct drm_mm_node *
> -first_hole(struct drm_mm *mm,
> -	   u64 start, u64 end, u64 size,
> -	   enum drm_mm_insert_mode mode)
> +struct drm_mm_node *
> +drm_mm_first_hole(struct drm_mm *mm,
> +		  u64 start, u64 end, u64 size,
> +		  enum drm_mm_insert_mode mode)
>   {
>   	switch (mode) {
>   	default:
> @@ -374,6 +374,7 @@ first_hole(struct drm_mm *mm,
>   						hole_stack);
>   	}
>   }
> +EXPORT_SYMBOL(drm_mm_first_hole);
>   
>   /**
>    * DECLARE_NEXT_HOLE_ADDR - macro to declare next hole functions
> @@ -410,11 +411,11 @@ static struct drm_mm_node *name(struct drm_mm_node *entry, u64 size)	\
>   DECLARE_NEXT_HOLE_ADDR(next_hole_high_addr, rb_left, rb_right)
>   DECLARE_NEXT_HOLE_ADDR(next_hole_low_addr, rb_right, rb_left)
>   
> -static struct drm_mm_node *
> -next_hole(struct drm_mm *mm,
> -	  struct drm_mm_node *node,
> -	  u64 size,
> -	  enum drm_mm_insert_mode mode)
> +struct drm_mm_node *
> +drm_mm_next_hole(struct drm_mm *mm,
> +		 struct drm_mm_node *node,
> +		 u64 size,
> +		 enum drm_mm_insert_mode mode)
>   {
>   	switch (mode) {
>   	default:
> @@ -432,6 +433,7 @@ next_hole(struct drm_mm *mm,
>   		return &node->hole_stack == &mm->hole_stack ? NULL : node;
>   	}
>   }
> +EXPORT_SYMBOL(drm_mm_next_hole);

May need to add kerneldoc since first/next_hole are now exported, or 
perhaps double underscore them if DRM core allows that approach to kind 
of signify "it is exported by shouldn't really be used"? Question for 
dri-devel I guess.

>   
>   /**
>    * drm_mm_reserve_node - insert an pre-initialized node
> @@ -520,7 +522,6 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm,
>   {
>   	struct drm_mm_node *hole;
>   	u64 remainder_mask;
> -	bool once;
>   
>   	DRM_MM_BUG_ON(range_start > range_end);
>   
> @@ -533,13 +534,8 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm,
>   	if (alignment <= 1)
>   		alignment = 0;
>   
> -	once = mode & DRM_MM_INSERT_ONCE;
> -	mode &= ~DRM_MM_INSERT_ONCE;
> -
>   	remainder_mask = is_power_of_2(alignment) ? alignment - 1 : 0;
> -	for (hole = first_hole(mm, range_start, range_end, size, mode);
> -	     hole;
> -	     hole = once ? NULL : next_hole(mm, hole, size, mode)) {
> +	drm_mm_for_each_best_hole(hole, mm, range_start, range_end, size, mode) {
>   		u64 hole_start = __drm_mm_hole_node_start(hole);
>   		u64 hole_end = hole_start + hole->hole_size;
>   		u64 adj_start, adj_end;
> diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
> index ac33ba1b18bc..5055447697fa 100644
> --- a/include/drm/drm_mm.h
> +++ b/include/drm/drm_mm.h
> @@ -322,6 +322,17 @@ static inline u64 __drm_mm_hole_node_end(const struct drm_mm_node *hole_node)
>   	return list_next_entry(hole_node, node_list)->start;
>   }
>   
> +struct drm_mm_node *
> +drm_mm_first_hole(struct drm_mm *mm,
> +		  u64 start, u64 end, u64 size,
> +		  enum drm_mm_insert_mode mode);
> +
> +struct drm_mm_node *
> +drm_mm_next_hole(struct drm_mm *mm,
> +		 struct drm_mm_node *node,
> +		 u64 size,
> +		 enum drm_mm_insert_mode mode);
> +
>   /**
>    * drm_mm_hole_node_end - computes the end of the hole following @node
>    * @hole_node: drm_mm_node which implicitly tracks the following hole
> @@ -400,6 +411,27 @@ static inline u64 drm_mm_hole_node_end(const struct drm_mm_node *hole_node)
>   	     1 : 0; \
>   	     pos = list_next_entry(pos, hole_stack))
>   
> +/**
> + * drm_mm_for_each_best_hole - iterator to optimally walk over all holes >= @size
> + * @pos: &drm_mm_node used internally to track progress
> + * @mm: &drm_mm allocator to walk
> + * @range_start: start of the allowed range for the allocation
> + * @range_end: end of the allowed range for the allocation
> + * @size: size of the allocation
> + * @mode: fine-tune the allocation search
> + *
> + * This iterator walks over all holes suitable for the allocation of given
> + * @size in a very efficient manner. It is implemented by calling
> + * drm_mm_first_hole() and drm_mm_next_hole() which identify the
> + * appropriate holes within the given range by efficently traversing the
> + * rbtree associated with @mm.
> + */
> +#define drm_mm_for_each_best_hole(pos, mm, range_start, range_end, size, mode) \

Probably should not have "best" in the name since the mode is passed in 
by the caller.

> +	for (pos = drm_mm_first_hole(mm, range_start, range_end, size, mode); \
> +	     pos; \
> +	     pos = mode & DRM_MM_INSERT_ONCE ? \
> +	     NULL : drm_mm_next_hole(mm, hole, size, mode))

I think you would need to modify the first/next_hole to mask out 
DRM_MM_INSERT_ONCE, otherwise it probably does not work as it stands.

Regards,

Tvrtko

> +
>   /*
>    * Basic range manager support (drm_mm.c)
>    */