[Intel-gfx] [PATCH 3/4] drm/i915: Add support for stealing purgable stolen pages

[Chris Wilson]

On Tue, Sep 15, 2015 at 02:03:26PM +0530, ankitprasad.r.sharma at intel.com wrote:
> -struct drm_i915_gem_object *
> -i915_gem_object_create_stolen(struct drm_device *dev, u64 size)
> +static bool mark_free(struct drm_i915_gem_object *obj, struct list_head *unwind)
> +{
> +	if (obj->stolen == NULL)
> +		return false;

BUG_ON(obj->stolen == NULL);

> +
> +	if (obj->madv != I915_MADV_DONTNEED)
> +		return false;
> +
> +	if (obj->pin_display)
> +		return false;
> +
> +	if (I915_BO_IS_ACTIVE(obj))
> +		return false;

We want to add both active/inactive objects (ordering by the caller to
prioritise inactive objects).

> +	list_add(&obj->tmp_link, unwind);
> +	return drm_mm_scan_add_block(&obj->stolen->base);
> +}
> +
> +static int
> +stolen_evict(struct drm_i915_private *dev_priv, u64 size)
>  {
> -	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_i915_gem_object *obj;
> -	struct drm_mm_node *stolen;
> +	struct list_head unwind, evict;
> +	struct i915_stolen_node *iter;
>  	int ret;
>  
> -	if (!drm_mm_initialized(&dev_priv->mm.stolen))
> -		return NULL;
> +	drm_mm_init_scan(&dev_priv->mm.stolen, size, 0, 0);
> +	INIT_LIST_HEAD(&unwind);
> +
> +	list_for_each_entry(iter, &dev_priv->mm.stolen_list, mm_link) {
> +		if (I915_BO_IS_ACTIVE(iter->obj))
> +			continue;
> +
> +		if (mark_free(iter->obj, &unwind))
> +			goto found;
> +	}
> +
> +	list_for_each_entry(iter, &dev_priv->mm.stolen_list, mm_link) {
> +		if (!I915_BO_IS_ACTIVE(iter->obj))
> +			continue;
> +
> +		if (mark_free(iter->obj, &unwind))
> +			goto found;
> +	}

If I have my micro-optimising hat on, I would actually rewrite this as
soemthing like:

for (int phase = 0; phase <= 1; phase++) {
	list_for_each_entry(iter, &dev_priv->mm.stolen_list, mm_link) {
		if (I915_BO_IS_ACTIVE(iter->obj) != phase)
			continue;

		if (mark_free(iter->obj, &unwind))
			goto found;
	}
}

as the compiler will find that easier to perform magic with. We also
probably want to do i915_gem_retire_requests() first (so that any
recently idle objects are moved to the front queue).

> +found:
> +	INIT_LIST_HEAD(&evict);
> +	while (!list_empty(&unwind)) {
> +		obj = list_first_entry(&unwind,
> +				       struct drm_i915_gem_object,
> +				       tmp_link);
> +		list_del_init(&obj->tmp_link);

The fun thing with tmp_link is that we don't need to set it to clear
(either here or during object construction).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre