Re: [PATCH] drm/i915/ttm: consider all placements for the page alignment

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 6/22/21 11:58 AM, Matthew Auld wrote:
> Just checking the current region is not enough, if we later migrate the
> object somewhere else. For example if the placements are {SMEM, LMEM},
> then we might get this wrong. Another idea might be to make the
> page_alignment part of the ttm_place, instead of the BO.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 21 ++++++++++++++++++++-
>   1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index c5deb8b7227c..5d894bba6430 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -753,6 +753,25 @@ void i915_ttm_bo_destroy(struct ttm_buffer_object *bo)
>   		call_rcu(&obj->rcu, __i915_gem_free_object_rcu);
>   }
>   
> +static u64 i915_gem_object_page_size(struct drm_i915_gem_object *obj)
> +{
> +	u64 page_size;
> +	int i;
> +
> +	if (!obj->mm.n_placements)
> +		return obj->mm.region->min_page_size;
> +
> +	page_size = 0;
> +	for (i = 0; i < obj->mm.n_placements; i++) {
> +		struct intel_memory_region *mr = obj->mm.placements[i];
> +
> +		page_size = max_t(u64, mr->min_page_size, page_size);
> +	}
> +
> +	GEM_BUG_ON(!page_size);
> +	return page_size;
> +}
> +
>   /**
>    * __i915_gem_ttm_object_init - Initialize a ttm-backed i915 gem object
>    * @mem: The initial memory region for the object.
> @@ -793,7 +812,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
>   	obj->base.vma_node.driver_private = i915_gem_to_ttm(obj);
>   	ret = ttm_bo_init(&i915->bdev, i915_gem_to_ttm(obj), size,
>   			  bo_type, &i915_sys_placement,
> -			  mem->min_page_size >> PAGE_SHIFT,
> +			  i915_gem_object_page_size(obj) >> PAGE_SHIFT,

Hmm, can't we just have the buddy manager silently enforce its 
min_page_size?

/Thomas