Re: [PATCH v9 4/6] drm: implement a method to free unused pages

On 19/01/2022 11:37, 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.

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

v5(Matthew Auld):

• revert drm_buddy_block_trim() function return type changes in v4
• modify drm_buddy_block_trim() passing argument n_pages to original_size as n_pages has already been rounded up to the next power-of-two and passing n_pages results noop

v6:

• fix warnings reported by kernel test robot lkp@intel.com

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

drivers/gpu/drm/drm_buddy.c | 65 +++++++++++++++++++ drivers/gpu/drm/i915/i915_ttm_buddy_manager.c | 10 +++ include/drm/drm_buddy.h | 4 ++ 3 files changed, 79 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c index 6aa5c1ce25bf..c5902a81b8c5 100644 --- a/drivers/gpu/drm/drm_buddy.c +++ b/drivers/gpu/drm/drm_buddy.c @@ -546,6 +546,71 @@ static int __drm_buddy_alloc_range(struct drm_buddy *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

@blocks: Input and output list of allocated blocks. MUST contain single block as input to be trimmed. On success will contain the newly allocated blocks making up the @new_size. Blocks always appear in ascending order.

?

• • 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.

so remaining portions are unused and can be optionally freed with this function.

?

• • Returns:
• • 0 on success, error code on failure.
• */

+int drm_buddy_block_trim(struct drm_buddy *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 -EINVAL;
  

• block = list_first_entry(blocks,

• 		 struct drm_buddy_block,
  

• 		 link);
  

• if (!drm_buddy_block_is_allocated(block))

Maybe:

if (WARN_ON(!drm_buddy_block_is_allocated()))

AFAIK it should be normally impossible to be handed such non-allocated block, and so should be treated as a serious programmer error.

?

• return -EINVAL;
  

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

• return -EINVAL;
  

• if (!new_size && !IS_ALIGNED(new_size, mm->chunk_size))

• return -EINVAL;
  

I assume that's a typo:

if (!new_size || ...)

Otherwise I think looks good. Some unit tests for this would be nice, but not a blocker. And this does at least pass the igt_mock_contiguous selftest, and I didn't see anything nasty when running on DG1, which does make use of TTM_PL_FLAG_CONTIGUOUS, Reviewed-by: Matthew Auld matthew.auld@intel.com

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

• return 0;
  

• 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;
• return err;

+} +EXPORT_SYMBOL(drm_buddy_block_trim);

• /**
  • drm_buddy_alloc_blocks - 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 3662434b64bb..53eb100688a6 100644 --- a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c +++ b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c @@ -97,6 +97,16 @@ 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) {

• u64 original_size = (u64)bman_res->base.num_pages << PAGE_SHIFT;
  

• mutex_lock(&bman->lock);
  

• drm_buddy_block_trim(mm,
  

• 		     original_size,
  

• 		     &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 424fc443115e..17ca928fce8e 100644 --- a/include/drm/drm_buddy.h +++ b/include/drm/drm_buddy.h @@ -145,6 +145,10 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm, struct list_head *blocks, unsigned long flags);

+int drm_buddy_block_trim(struct drm_buddy *mm,

• 	 u64 new_size,
  

• 	 struct list_head *blocks);
  

• void drm_buddy_free_block(struct drm_buddy *mm, struct drm_buddy_block *block);

  void drm_buddy_free_list(struct drm_buddy *mm, struct list_head *objects);