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

[Arunpravin]

> -----Original Message-----
> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Matthew Auld
> Sent: Thursday, January 20, 2022 11:05 PM
> To: Paneer Selvam, Arunpravin <Arunpravin.PaneerSelvam at amd.com>; dri-devel at lists.freedesktop.org; intel-gfx at lists.freedesktop.org; amd-gfx at lists.freedesktop.org
> Cc: Deucher, Alexander <Alexander.Deucher at amd.com>; tzimmermann at suse.de; jani.nikula at linux.intel.com; Koenig, Christian <Christian.Koenig at amd.com>; daniel at ffwll.ch
> Subject: 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 at intel.com>
>>
>> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam at 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,

Good to hear its running on DG1, all changes are added to v10. working
on moving i915 buddy selftests into drm selftest folder, I will add a
new unit test case for trim function
> Reviewed-by: Matthew Auld <matthew.auld at 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);
>>