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

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

On Fri, Dec 05, 2025 at 08:41:13AM +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.
> 
> 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>
> ---
>  drivers/gpu/drm/xe/xe_ttm_vram_mgr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> index 9f70802fce92..ef6cfb8af0ac 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 we set this flag can we remove the logic which rounds the allocation
size to a pow2 and trims if TTM_PL_FLAG_CONTIGUOUS is set? From a quick
look it looks we can as drm_buddy has roundup / trim logic if
DRM_BUDDY_CONTIGUOUS_ALLOCATION is set.

Matt

> +
>  	if (place->fpfn || lpfn != man->size >> PAGE_SHIFT)
>  		vres->flags |= DRM_BUDDY_RANGE_ALLOCATION;
>  
> -- 
> 2.52.0
>