[Intel-gfx] [PATCH 5/5] drm/i915: Use partial view in mmap fault handler

[Chris Wilson]

On Fri, Apr 24, 2015 at 03:10:20PM +0300, Joonas Lahtinen wrote:
> Use partial view for huge BOs (bigger than half the mappable aperture)
> in fault handler so that they can be accessed withough trying to make
> room for them by evicting other objects.
> 
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c |   67 ++++++++++++++++++++++++++-------------
>  1 file changed, 45 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index c2c1819..eb30cee 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1635,6 +1635,7 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  	struct drm_i915_gem_object *obj = to_intel_bo(vma->vm_private_data);
>  	struct drm_device *dev = obj->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct i915_ggtt_view view = i915_ggtt_view_normal;
>  	pgoff_t page_offset;
>  	unsigned long pfn;
>  	int ret = 0;
> @@ -1667,8 +1668,21 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  		goto unlock;
>  	}
>  
> -	/* Now bind it into the GTT if needed */
> -	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> +	/* Use a partial view if the object is bigger than half the aperture. */
> +	if (obj->base.size > dev_priv->gtt.mappable_end/2) {
> +		static const size_t chunk_size = 256; // 1 MiB
> +		memset(&view, 0, sizeof(view));
> +		view.type = I915_GGTT_VIEW_PARTIAL;
> +		view.params.partial.offset = rounddown(page_offset, chunk_size);
> +		view.params.partial.size =
> +			min_t(size_t,
> +			      chunk_size,
> +			      (vma->vm_end - vma->vm_start)/PAGE_SIZE -
> +			      view.params.partial.offset);

This isn't what I was imagining.

I was expecting to see error handling inside the fault path if we could
not pin the object. This way we could handle fragmentation or display
objects pinned outside the aperture.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre