[PATCH] drm: round_up the size to the alignment value

[Arunpravin Paneer Selvam]

On 30/03/22 2:42 pm, Christian König wrote:
> Am 30.03.22 um 11:20 schrieb Arunpravin Paneer Selvam:
>>
>> On 30/03/22 2:37 pm, Christian König wrote:
>>> Am 30.03.22 um 11:04 schrieb Arunpravin Paneer Selvam:
>>>> Round up the size value to the min_page_size and trim the last block to
>>>> the required size.
>>>>
>>>> This solves a bug detected when size is not aligned with the min_page_size.
>>>> Unigine Heaven has allocation requests for example required pages are 257
>>>> and alignment request is 256. To allocate the left over 1 page, continues
>>>> the iteration to find the order value which is 0 and when it compares with
>>>> min_order = 8, triggers the BUG_ON(order < min_order). To avoid this issue
>>>> we round_up the size value to the min_page_size and trim the last block to
>>>> the computed required size value.
>>> Well, Matthew and you convinced me to *not* do it like this.
>>>
>>> Has that conclusion changed somehow?
>>>
>> Yes, now he is ok to handle rounding + trimming in drm buddy
> 
> Yeah, but I'm no longer :)
> 
> How do we then handle the detection of contiguous allocation?
> 
> As I said we can do that like:
> 1. alloc
> 2. check if we only have a single node
I think verifying the list is a single node would allow all the power of
2 requests(1 page, 2 pages, 4 pages etc..) single node and CONTIGUOUS
flag not enabled cases entering into the trim function and simply return
since the original size == roundup_pow_of_2 size.

can we handle all the situation (alignment rounding trimming +
contiguous trimming) in a single if condition like below,

if (cur_size != (pages << PAGE_SHIFT))

where cur_size = stores the size value before round_up(alignment
rounding up) or round_pow_of_2 (contiguous rounding up)

pages = stores the size value after round_up(alignment rounding up) or
round_pow_of_2 (contiguous rounding up)

if there is a difference b/w these 2 numbers, we enter the trim block -
- For a single node, we pass the original size (contiguous trimming)
- For multiple node, we fetch the last block and trim the computed size
(alignment rounding trimming)


> 3. trim
> 
> But if we include the trim here we can't do it any more.
> 
> Only alternative would then be to inspect each node and see if it 
> follows directly behind the predecessor.
> 

ok. Therefore, we handle both contiguous allocation trimming and
alignment rounding up trimming (only last block) in amdgpu and i915 driver.

And, in drm buddy we just have a check to return -EINVAL if size is not
aligned to min_page_size.

If yes to above statements, I included alignment rounding up trimming
(only last block) in the same place where currently we trim for the
contiguous allocation. I will send the patch for review.
> Regards,
> Christian.
> 
>>
>>> Regards,
>>> Christian.
>>>
>>>> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
>>>> ---
>>>>    drivers/gpu/drm/drm_buddy.c | 31 +++++++++++++++++++++++++++++++
>>>>    1 file changed, 31 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>>>> index 72f52f293249..98d7ec359b08 100644
>>>> --- a/drivers/gpu/drm/drm_buddy.c
>>>> +++ b/drivers/gpu/drm/drm_buddy.c
>>>> @@ -641,6 +641,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>>>>    	unsigned int min_order, order;
>>>>    	unsigned long pages;
>>>>    	LIST_HEAD(allocated);
>>>> +	u64 cur_size;
>>>>    	int err;
>>>>    
>>>>    	if (size < mm->chunk_size)
>>>> @@ -665,6 +666,11 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>>>>    	if (start + size == end)
>>>>    		return __drm_buddy_alloc_range(mm, start, size, blocks);
>>>>    
>>>> +	cur_size = size;
>>>> +
>>>> +	if (!IS_ALIGNED(size, min_page_size))
>>>> +		size = round_up(size, min_page_size);
>>>> +
>>>>    	pages = size >> ilog2(mm->chunk_size);
>>>>    	order = fls(pages) - 1;
>>>>    	min_order = ilog2(min_page_size) - ilog2(mm->chunk_size);
>>>> @@ -702,6 +708,31 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>>>>    			break;
>>>>    	} while (1);
>>>>    
>>>> +
>>>> +	/*
>>>> +	 * If size value rounded up to min_page_size, trim the last block
>>>> +	 * to the required size
>>>> +	 */
>>>> +	if (cur_size != size) {
>>>> +		struct drm_buddy_block *trim_block;
>>>> +		LIST_HEAD(trim_list);
>>>> +		u64 required_size;
>>>> +
>>>> +		trim_block = list_last_entry(&allocated, typeof(*trim_block), link);
>>>> +		list_move_tail(&trim_block->link, &trim_list);
>>>> +		/*
>>>> +		 * Compute the required_size value by subtracting the last block size
>>>> +		 * with (aligned size - original size)
>>>> +		 */
>>>> +		required_size = drm_buddy_block_size(mm, trim_block) - (size - cur_size);
>>>> +
>>>> +		drm_buddy_block_trim(mm,
>>>> +				     required_size,
>>>> +				     &trim_list);
>>>> +
>>>> +		list_splice_tail(&trim_list, &allocated);
>>>> +	}
>>>> +
>>>>    	list_splice_tail(&allocated, blocks);
>>>>    	return 0;
>>>>    
>>>>
>>>> base-commit: ec57376fba5abc0e571617ff88e2ade7970c2e4b
>