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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 09/15/2015 09:33 AM, ankitprasad.r.sharma@intel.com wrote:
> From: Chris Wilson <chris at chris-wilson.co.uk>
>
> If we run out of stolen memory when trying to allocate an object, see if
> we can reap enough purgeable objects to free up enough contiguous free
> space for the allocation. This is in principle very much like evicting
> objects to free up enough contiguous space in the vma when binding
> a new object - and you will be forgiven for thinking that the code looks
> very similar.
>
> At the moment, we do not allow userspace to allocate objects in stolen,
> so there is neither the memory pressure to trigger stolen eviction nor
> any purgeable objects inside the stolen arena. However, this will change
> in the near future, and so better management and defragmentation of
> stolen memory will become a real issue.
>
> v2: Remember to remove the drm_mm_node.
>
> v3: Rebased to the latest drm-intel-nightly (Ankit)
>
> v4: corrected if-else braces format (Tvrtko/kerneldoc)
>
> v5: Rebased to the latest drm-intel-nightly (Ankit)
> Added a seperate list to maintain purgable objects from stolen memory
> region (Chris/Daniel)
>
> Testcase: igt/gem_stolen
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c    |   4 +-
>   drivers/gpu/drm/i915/i915_drv.h        |  17 +++-
>   drivers/gpu/drm/i915/i915_gem.c        |  16 +++
>   drivers/gpu/drm/i915/i915_gem_stolen.c | 176 ++++++++++++++++++++++++++++-----
>   drivers/gpu/drm/i915/intel_pm.c        |   4 +-
>   5 files changed, 187 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 7a28de5..0db8c47 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -179,7 +179,7 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
>   			seq_puts(m, ")");
>   	}
>   	if (obj->stolen)
> -		seq_printf(m, " (stolen: %08llx)", obj->stolen->start);
> +		seq_printf(m, " (stolen: %08llx)", obj->stolen->base.start);
>   	if (obj->pin_display || obj->fault_mappable) {
>   		char s[3], *t = s;
>   		if (obj->pin_display)
> @@ -258,7 +258,7 @@ static int obj_rank_by_stolen(void *priv,
>   	struct drm_i915_gem_object *b =
>   		container_of(B, struct drm_i915_gem_object, obj_exec_link);
>
> -	return a->stolen->start - b->stolen->start;
> +	return a->stolen->base.start - b->stolen->base.start;
>   }
>
>   static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index e6ef083..37ee32d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -841,6 +841,12 @@ struct i915_ctx_hang_stats {
>   	bool banned;
>   };
>
> +struct i915_stolen_node {
> +	struct drm_mm_node base;
> +	struct list_head mm_link;
> +	struct drm_i915_gem_object *obj;
> +};
> +
>   /* This must match up with the value previously used for execbuf2.rsvd1. */
>   #define DEFAULT_CONTEXT_HANDLE 0
>
> @@ -1268,6 +1274,13 @@ struct i915_gem_mm {
>   	 */
>   	struct list_head unbound_list;
>
> +	/**
> +	 * List of stolen objects that have been marked as purgeable and
> +	 * thus available for reaping if we need more space for a new
> +	 * allocation. Ordered by time of marking purgeable.
> +	 */
> +	struct list_head stolen_list;
> +
>   	/** Usable portion of the GTT for GEM */
>   	unsigned long stolen_base; /* limited to low memory (32-bit) */
>
> @@ -2026,7 +2039,7 @@ struct drm_i915_gem_object {
>   	struct list_head vma_list;
>
>   	/** Stolen memory for this object, instead of being backed by shmem. */
> -	struct drm_mm_node *stolen;
> +	struct i915_stolen_node *stolen;
>   	struct list_head global_list;
>
>   	struct list_head ring_list[I915_NUM_RINGS];
> @@ -2034,6 +2047,7 @@ struct drm_i915_gem_object {
>   	struct list_head obj_exec_link;
>
>   	struct list_head batch_pool_link;
> +	struct list_head tmp_link;
>
>   	/**
>   	 * This is set if the object is on the active lists (has pending
> @@ -2150,6 +2164,7 @@ struct drm_i915_gem_object {
>   	};
>   };
>   #define to_intel_bo(x) container_of(x, struct drm_i915_gem_object, base)
> +#define I915_BO_IS_ACTIVE(__obj) (__obj->active)
>
>   void i915_gem_track_fb(struct drm_i915_gem_object *old,
>   		       struct drm_i915_gem_object *new,
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6568a7f..85025b1 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4228,6 +4228,20 @@ i915_gem_madvise_ioctl(struct drm_device *dev, void *data,
>   	if (obj->madv == I915_MADV_DONTNEED && obj->pages == NULL)
>   		i915_gem_object_truncate(obj);
>
> +	if (obj->stolen) {
> +		switch (obj->madv) {
> +		case I915_MADV_WILLNEED:
> +			list_del_init(&obj->stolen->mm_link);
> +			break;
> +		case I915_MADV_DONTNEED:
> +			list_move(&obj->stolen->mm_link,
> +				  &dev_priv->mm.stolen_list);
> +			break;
> +		default:
> +			break;
> +		}
> +	}
> +
>   	args->retained = obj->madv != __I915_MADV_PURGED;
>
>   out:
> @@ -4248,6 +4262,7 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
>   	INIT_LIST_HEAD(&obj->obj_exec_link);
>   	INIT_LIST_HEAD(&obj->vma_list);
>   	INIT_LIST_HEAD(&obj->batch_pool_link);
> +	INIT_LIST_HEAD(&obj->tmp_link);
>
>   	obj->ops = ops;
>
> @@ -4898,6 +4913,7 @@ i915_gem_load(struct drm_device *dev)
>   	INIT_LIST_HEAD(&dev_priv->context_list);
>   	INIT_LIST_HEAD(&dev_priv->mm.unbound_list);
>   	INIT_LIST_HEAD(&dev_priv->mm.bound_list);
> +	INIT_LIST_HEAD(&dev_priv->mm.stolen_list);
>   	INIT_LIST_HEAD(&dev_priv->mm.fence_list);
>   	for (i = 0; i < I915_NUM_RINGS; i++)
>   		init_ring_lists(&dev_priv->ring[i]);
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index 99f2bce..430e0b0 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -52,8 +52,8 @@ int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
>   		return -ENODEV;
>
>   	mutex_lock(&dev_priv->mm.stolen_lock);
> -	ret = drm_mm_insert_node(&dev_priv->mm.stolen, node, size, alignment,
> -				 DRM_MM_SEARCH_DEFAULT);
> +	ret = drm_mm_insert_node(&dev_priv->mm.stolen, node,
> +				 size, alignment, DRM_MM_SEARCH_DEFAULT);

There is no change here.

>   	mutex_unlock(&dev_priv->mm.stolen_lock);
>
>   	return ret;
> @@ -407,18 +407,19 @@ static void i915_gem_object_put_pages_stolen(struct drm_i915_gem_object *obj)
>   	kfree(obj->pages);
>   }
>
> -
 >
>   static void
>   i915_gem_object_release_stolen(struct drm_i915_gem_object *obj)
>   {
>   	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
>
>   	if (obj->stolen) {
> -		i915_gem_stolen_remove_node(dev_priv, obj->stolen);
> +		list_del(&obj->stolen->mm_link);
> +		i915_gem_stolen_remove_node(dev_priv, &obj->stolen->base);
>   		kfree(obj->stolen);
>   		obj->stolen = NULL;
>   	}
>   }
> +
>   static const struct drm_i915_gem_object_ops i915_gem_object_stolen_ops = {
>   	.get_pages = i915_gem_object_get_pages_stolen,
>   	.put_pages = i915_gem_object_put_pages_stolen,
> @@ -427,7 +428,7 @@ static const struct drm_i915_gem_object_ops i915_gem_object_stolen_ops = {
>
>   static struct drm_i915_gem_object *
>   _i915_gem_object_create_stolen(struct drm_device *dev,
> -			       struct drm_mm_node *stolen)
> +			       struct i915_stolen_node *stolen)
>   {
>   	struct drm_i915_gem_object *obj;
>
> @@ -435,17 +436,21 @@ _i915_gem_object_create_stolen(struct drm_device *dev,
>   	if (obj == NULL)
>   		return NULL;
>
> -	drm_gem_private_object_init(dev, &obj->base, stolen->size);
> +	drm_gem_private_object_init(dev, &obj->base, stolen->base.size);
>   	i915_gem_object_init(obj, &i915_gem_object_stolen_ops);
>
>   	obj->pages = i915_pages_create_for_stolen(dev,
> -						  stolen->start, stolen->size);
> +						  stolen->base.start,
> +						  stolen->base.size);
>   	if (obj->pages == NULL)
>   		goto cleanup;
>
>   	i915_gem_object_pin_pages(obj);
>   	obj->stolen = stolen;
>
> +	stolen->obj = obj;
> +	INIT_LIST_HEAD(&stolen->mm_link);
> +
>   	obj->base.read_domains = I915_GEM_DOMAIN_CPU | I915_GEM_DOMAIN_GTT;
>   	obj->cache_level = HAS_LLC(dev) ? I915_CACHE_LLC : I915_CACHE_NONE;
>
> @@ -456,36 +461,157 @@ cleanup:
>   	return NULL;
>   }
>
> -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;

As Chris said, just WARN_ON instead of BUG_ON please.

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

Chris already spotted this will prevent callers from working as they expect.

> +	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;
> +	}
 > +
> +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);
> +
> +		if (drm_mm_scan_remove_block(&obj->stolen->base)) {
> +			list_add(&obj->tmp_link, &evict);
> +			drm_gem_object_reference(&obj->base);
> +		}

In what circumstances can drm_mm_scan_remove_block fail?

> +	}
> +
> +	ret = 0;
> +	while (!list_empty(&evict)) {
> +		obj = list_first_entry(&evict,
> +				       struct drm_i915_gem_object,
> +				       tmp_link);
> +		list_del_init(&obj->tmp_link);
> +
> +		if (ret == 0) {
> +			struct i915_vma *vma, *vma_next;
> +
> +			list_for_each_entry_safe(vma, vma_next,
> +						 &obj->vma_list,
> +						 vma_link)
> +				if (i915_vma_unbind(vma))
> +					break;

Because of VMA unbinding stolen creation now again needs struct_mutex. I 
think putting held assertion somewhere in the call chain is now appropriate.

The rest looked good to me.

Regards,

Tvrtko
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