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

Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> · Wed, 2 Feb 2022 13:04:16 +0000

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@xxxxxxxxxxxxxxx>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
  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)
   */






