Re: [PATCH 4/4] drm/i915: Invalidate our pages under memory pressure

[Robert Beckett <robert.beckett@intel.com>]

On 25/03/2014 13:23, Chris Wilson wrote:
> Try to flush out dirty pages into the swapcache (and from there into the
> swapfile) when under memory pressure and forced to drop GEM objects from
> memory. In effect, this should just allow us to discard unused pages for
> memory reclaim and to start writeback earlier.
>
> v2: Hugh Dickins warned that explicitly starting writeback from
> shrink_slab was prone to deadlocks within shmemfs.
>
> Cc: Hugh Dickins <hughd@google.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 38 +++++++++++++++++++++++++++-----------
>   1 file changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 135ee8bd55f6..8287fd6701c6 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -60,7 +60,6 @@ static unsigned long i915_gem_shrinker_scan(struct shrinker *shrinker,
>   					    struct shrink_control *sc);
>   static unsigned long i915_gem_purge(struct drm_i915_private *dev_priv, long target);
>   static unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv);
> -static void i915_gem_object_truncate(struct drm_i915_gem_object *obj);
>   static void i915_gem_retire_requests_ring(struct intel_ring_buffer *ring);
>
>   static bool cpu_cache_is_coherent(struct drm_device *dev,
> @@ -1685,12 +1684,16 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
>   	return i915_gem_mmap_gtt(file, dev, args->handle, &args->offset);
>   }
>
> +static inline int
> +i915_gem_object_is_purgeable(struct drm_i915_gem_object *obj)
> +{
> +	return obj->madv == I915_MADV_DONTNEED;
> +}
> +
>   /* Immediately discard the backing storage */
>   static void
>   i915_gem_object_truncate(struct drm_i915_gem_object *obj)
>   {
> -	struct inode *inode;
> -
>   	i915_gem_object_free_mmap_offset(obj);
>
>   	if (obj->base.filp == NULL)
> @@ -1701,16 +1704,28 @@ i915_gem_object_truncate(struct drm_i915_gem_object *obj)
>   	 * To do this we must instruct the shmfs to drop all of its
>   	 * backing pages, *now*.
>   	 */
> -	inode = file_inode(obj->base.filp);
> -	shmem_truncate_range(inode, 0, (loff_t)-1);
> -
> +	shmem_truncate_range(file_inode(obj->base.filp), 0, (loff_t)-1);
>   	obj->madv = __I915_MADV_PURGED;
>   }
>
> -static inline int
> -i915_gem_object_is_purgeable(struct drm_i915_gem_object *obj)
> +/* Try to discard unwanted pages */
> +static void
> +i915_gem_object_invalidate(struct drm_i915_gem_object *obj)
>   {
> -	return obj->madv == I915_MADV_DONTNEED;
> +	struct address_space *mapping;
> +
> +	switch (obj->madv) {
> +	case I915_MADV_DONTNEED:
> +		i915_gem_object_truncate(obj);
> +	case __I915_MADV_PURGED:
> +		return;
> +	}
> +
> +	if (obj->base.filp == NULL)
> +		return;
> +
> +	mapping = file_inode(obj->base.filp)->i_mapping,
> +	invalidate_mapping_pages(mapping, 0, (loff_t)-1);
>   }
>
>   static void
> @@ -1775,8 +1790,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
>   	ops->put_pages(obj);
>   	obj->pages = NULL;
>
> -	if (i915_gem_object_is_purgeable(obj))
> -		i915_gem_object_truncate(obj);
> +	i915_gem_object_invalidate(obj);
>
>   	return 0;
>   }
> @@ -4201,6 +4215,8 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
>
>   	if (WARN_ON(obj->pages_pin_count))
>   		obj->pages_pin_count = 0;
> +	if (obj->madv != __I915_MADV_PURGED)
> +		obj->madv = I915_MADV_DONTNEED;
>   	i915_gem_object_put_pages(obj);
>   	i915_gem_object_free_mmap_offset(obj);
>   	i915_gem_object_release_stolen(obj);
>

Functionally it looks good to me.

Though, you may want a /* fall-through */ comment (some people cant 
mentally parse fallthroughs without being prompted) and a default: 
break; (to avoid any static code analysis complaints) in the switch in 
i915_gem_object_invalidate.

Reviewed-by: Robert Beckett <robert.beckett@intel.com>