[PATCH v6 4/6] drm: implement a method to free unused pages

[Arunpravin <Arunpravin.PaneerSelvam@amd.com>]

On contiguous allocation, we round up the size
to the *next* power of 2, implement a function
to free the unused pages after the newly allocate block.

v2(Matthew Auld):
  - replace function name 'drm_buddy_free_unused_pages' with
    drm_buddy_block_trim
  - replace input argument name 'actual_size' with 'new_size'
  - add more validation checks for input arguments
  - add overlaps check to avoid needless searching and splitting
  - merged the below patch to see the feature in action
     - add free unused pages support to i915 driver
  - lock drm_buddy_block_trim() function as it calls mark_free/mark_split
    are all globally visible

v3(Matthew Auld):
  - remove trim method error handling as we address the failure case
    at drm_buddy_block_trim() function

v4:
  - in case of trim, at __alloc_range() split_block failure path
    marks the block as free and removes it from the original list,
    potentially also freeing it, to overcome this problem, we turn
    the drm_buddy_block_trim() input node into a temporary node to
    prevent recursively freeing itself, but still retain the
    un-splitting/freeing of the other nodes(Matthew Auld)

  - modify the drm_buddy_block_trim() function return type

Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
---
 drivers/gpu/drm/drm_buddy.c                   | 61 +++++++++++++++++++
 drivers/gpu/drm/i915/i915_ttm_buddy_manager.c |  8 +++
 include/drm/drm_buddy.h                       |  4 ++
 3 files changed, 73 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index eddc1eeda02e..855afcaf7edd 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -538,6 +538,67 @@ static int __drm_buddy_alloc_range(struct drm_buddy_mm *mm,
 	return __alloc_range(mm, &dfs, start, size, blocks);
 }
 
+/**
+ * drm_buddy_block_trim - free unused pages
+ *
+ * @mm: DRM buddy manager
+ * @new_size: original size requested
+ * @blocks: output list head to add allocated blocks
+ *
+ * For contiguous allocation, we round up the size to the nearest
+ * power of two value, drivers consume *actual* size, so remaining
+ * portions are unused and it can be freed.
+ */
+void drm_buddy_block_trim(struct drm_buddy_mm *mm,
+			  u64 new_size,
+			  struct list_head *blocks)
+{
+	struct drm_buddy_block *parent;
+	struct drm_buddy_block *block;
+	LIST_HEAD(dfs);
+	u64 new_start;
+	int err;
+
+	if (!list_is_singular(blocks))
+		return;
+
+	block = list_first_entry(blocks,
+				 struct drm_buddy_block,
+				 link);
+
+	if (!drm_buddy_block_is_allocated(block))
+		return;
+
+	if (new_size > drm_buddy_block_size(mm, block))
+		return;
+
+	if (!new_size && !IS_ALIGNED(new_size, mm->chunk_size))
+		return;
+
+	if (new_size == drm_buddy_block_size(mm, block))
+		return;
+
+	list_del(&block->link);
+	mark_free(mm, block);
+	mm->avail += drm_buddy_block_size(mm, block);
+
+	/* Prevent recursively freeing this node */
+	parent = block->parent;
+	block->parent = NULL;
+
+	new_start = drm_buddy_block_offset(block);
+	list_add(&block->tmp_link, &dfs);
+	err =  __alloc_range(mm, &dfs, new_start, new_size, blocks);
+	if (err) {
+		mark_allocated(block);
+		mm->avail -= drm_buddy_block_size(mm, block);
+		list_add(&block->link, blocks);
+	}
+
+	block->parent = parent;
+}
+EXPORT_SYMBOL(drm_buddy_block_trim);
+
 /**
  * drm_buddy_alloc - allocate power-of-two blocks
  *
diff --git a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
index 7c58efb60dba..05f924f32e96 100644
--- a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
+++ b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
@@ -97,6 +97,14 @@ static int i915_ttm_buddy_man_alloc(struct ttm_resource_manager *man,
 	if (unlikely(err))
 		goto err_free_blocks;
 
+	if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
+		mutex_lock(&bman->lock);
+		drm_buddy_block_trim(mm,
+				(u64)n_pages << PAGE_SHIFT,
+				&bman_res->blocks);
+		mutex_unlock(&bman->lock);
+	}
+
 	*res = &bman_res->base;
 	return 0;
 
diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
index f573b02304f4..703866a87939 100644
--- a/include/drm/drm_buddy.h
+++ b/include/drm/drm_buddy.h
@@ -146,6 +146,10 @@ int drm_buddy_alloc(struct drm_buddy_mm *mm,
 		    struct list_head *blocks,
 		    unsigned long flags);
 
+void drm_buddy_block_trim(struct drm_buddy_mm *mm,
+			  u64 new_size,
+			  struct list_head *blocks);
+
 void drm_buddy_free(struct drm_buddy_mm *mm, struct drm_buddy_block *block);
 
 void drm_buddy_free_list(struct drm_buddy_mm *mm, struct list_head *objects);
-- 
2.25.1