Re: [PATCH 5/8] drm: Implement method to free unused pages

On 25/10/2021 14:00, Arunpravin wrote:

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.

Signed-off-by: Arunpravin Arunpravin.PaneerSelvam@amd.com

Ideally this gets added with some user, so we can see it in action? Maybe squash the next patch here?

---

drivers/gpu/drm/drm_buddy.c | 103 ++++++++++++++++++++++++++++++++++++ include/drm/drm_buddy.h | 4 ++ 2 files changed, 107 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c index 9d3547bcc5da..0da8510736eb 100644 --- a/drivers/gpu/drm/drm_buddy.c +++ b/drivers/gpu/drm/drm_buddy.c @@ -284,6 +284,109 @@ static inline bool contains(u64 s1, u64 e1, u64 s2, u64 e2) return s1 <= s2 && e1 >= e2; }

+/**

• • drm_buddy_free_unused_pages - free unused pages
• • @mm: DRM buddy manager
• • @actual_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.
• • Returns:
• • 0 on success, error code on failure.
• */

+int drm_buddy_free_unused_pages(struct drm_buddy_mm *mm,

drm_buddy_block_trim?

• 		u64 actual_size,
  

new_size?

• 		struct list_head *blocks)
  

+{

• struct drm_buddy_block *block;
• struct drm_buddy_block *buddy;
• u64 actual_start;
• u64 actual_end;
• LIST_HEAD(dfs);
• u64 count = 0;
• int err;
• if (!list_is_singular(blocks))

• return -EINVAL;
  

• block = list_first_entry_or_null(blocks,

• 			 struct drm_buddy_block,
  

• 			 link);
  

• if (!block)

• return -EINVAL;
  

list_is_singular() already ensures that I guess?

• if (actual_size > drm_buddy_block_size(mm, block))

• return -EINVAL;
  

• if (actual_size == drm_buddy_block_size(mm, block))

• return 0;
  

Probably need to check the alignment of the actual_size, and also check that it is non-zero?

• list_del(&block->link);
• actual_start = drm_buddy_block_offset(block);
• actual_end = actual_start + actual_size - 1;
• if (drm_buddy_block_is_allocated(block))

That should rather be a programmer error.

• mark_free(mm, block);
  

• list_add(&block->tmp_link, &dfs);
• while (1) {

• block = list_first_entry_or_null(&dfs,
  

• 				 struct drm_buddy_block,
  

• 				 tmp_link);
  

• if (!block)
  

• 	break;
  

• list_del(&block->tmp_link);
  

• if (count == actual_size)
  

• 	return 0;
  

Check for overlaps somewhere here to avoid needless searching and splitting?

• if (contains(actual_start, actual_end, drm_buddy_block_offset(block),
  

• 	(drm_buddy_block_offset(block) + drm_buddy_block_size(mm, block) - 1))) {
  

Could maybe record the start/end for better readability?

• 	BUG_ON(!drm_buddy_block_is_free(block));
  

• 	/* Allocate only required blocks */
  

• 	mark_allocated(block);
  

• 	mm->avail -= drm_buddy_block_size(mm, block);
  

• 	list_add_tail(&block->link, blocks);
  

• 	count += drm_buddy_block_size(mm, block);
  

• 	continue;
  

• }
  

• if (drm_buddy_block_order(block) == 0)
  

• 	continue;
  

Should be impossible with overlaps check added.

• if (!drm_buddy_block_is_split(block)) {
  

That should always be true.

• 	err = split_block(mm, block);
  

• 	if (unlikely(err))
  

• 		goto err_undo;
  

• }
  

• list_add(&block->right->tmp_link, &dfs);
  

• list_add(&block->left->tmp_link, &dfs);
  

• }
• return -ENOSPC;

Would it make sense to factor out part of the alloc_range for this? It looks roughly the same.

+err_undo:

• buddy = get_buddy(block);
• if (buddy &&

•    (drm_buddy_block_is_free(block) &&
  

•     drm_buddy_block_is_free(buddy)))
  

• __drm_buddy_free(mm, block);
  

• return err;

Where do we add the block back to the original list? Did we not just leak it?

+} +EXPORT_SYMBOL(drm_buddy_free_unused_pages);

• static struct drm_buddy_block * alloc_range(struct drm_buddy_mm *mm, u64 start, u64 end,

diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h index cd8021d2d6e7..1dfc80c88e1f 100644 --- a/include/drm/drm_buddy.h +++ b/include/drm/drm_buddy.h @@ -145,6 +145,10 @@ int drm_buddy_alloc(struct drm_buddy_mm *mm, struct list_head *blocks, unsigned long flags);

+int drm_buddy_free_unused_pages(struct drm_buddy_mm *mm,

• 		u64 actual_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);