Re: [PATCH v2] drm/xe: Use DRM_BUDDY_CONTIGUOUS_ALLOCATION for contiguous allocations

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Dec 09, 2025 at 10:59:20PM +0530, Sanjay Yadav wrote:
> The VRAM/stolen memory managers do not currently set
> DRM_BUDDY_CONTIGUOUS_ALLOCATION for contiguous allocations. Enabling
> this flag activates the buddy allocator's try_harder path, which helps
> handle fragmented memory scenarios.
> 
> This enables the __alloc_contig_try_harder fallback in the buddy
> allocator, allowing contiguous allocation requests to succeed even when
> memory is fragmented by combining allocations from both(RHS and LHS)
> sides of a large free block.
> 
> v2: (Matt B)
> - Remove redundant logic for rounding allocation size and trimming when
>   TTM_PL_FLAG_CONTIGUOUS is set, since drm_buddy now handles this when
>   DRM_BUDDY_CONTIGUOUS_ALLOCATION is enabled
> 
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6713
> Suggested-by: Matthew Auld <matthew.auld@intel.com>
> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

But also please double check with Auld that this looks good to him.

Matt

> ---
>  drivers/gpu/drm/xe/xe_ttm_vram_mgr.c | 16 +++-------------
>  1 file changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> index 9f70802fce92..1a819b627afe 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> @@ -82,6 +82,9 @@ static int xe_ttm_vram_mgr_new(struct ttm_resource_manager *man,
>  	if (place->flags & TTM_PL_FLAG_TOPDOWN)
>  		vres->flags |= DRM_BUDDY_TOPDOWN_ALLOCATION;
>  
> +	if (place->flags & TTM_PL_FLAG_CONTIGUOUS)
> +		vres->flags |= DRM_BUDDY_CONTIGUOUS_ALLOCATION;
> +
>  	if (place->fpfn || lpfn != man->size >> PAGE_SHIFT)
>  		vres->flags |= DRM_BUDDY_RANGE_ALLOCATION;
>  
> @@ -111,25 +114,12 @@ static int xe_ttm_vram_mgr_new(struct ttm_resource_manager *man,
>  		goto error_unlock;
>  	}
>  
> -	if (place->fpfn + (size >> PAGE_SHIFT) != lpfn &&
> -	    place->flags & TTM_PL_FLAG_CONTIGUOUS) {
> -		size = roundup_pow_of_two(size);
> -		min_page_size = size;
> -
> -		lpfn = max_t(unsigned long, place->fpfn + (size >> PAGE_SHIFT), lpfn);
> -	}
> -
>  	err = drm_buddy_alloc_blocks(mm, (u64)place->fpfn << PAGE_SHIFT,
>  				     (u64)lpfn << PAGE_SHIFT, size,
>  				     min_page_size, &vres->blocks, vres->flags);
>  	if (err)
>  		goto error_unlock;
>  
> -	if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
> -		if (!drm_buddy_block_trim(mm, NULL, vres->base.size, &vres->blocks))
> -			size = vres->base.size;
> -	}
> -
>  	if (lpfn <= mgr->visible_size >> PAGE_SHIFT) {
>  		vres->used_visible_size = size;
>  	} else {
> -- 
> 2.52.0
>