drm/shmem: Add madvise state and purge helpers

Add support to the shmem GEM helpers for tracking madvise state and
purging pages. This is based on the msm implementation.

The BO provides a list_head, but the list management is handled outside
of the shmem helpers as there are different locking requirements.

Cc: Tomeu Vizoso <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Sean Paul <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Eric Anholt <[e-mail]>
Acked-by: Acked-by: Alyssa Rosenzweig <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_gem_shmem_helper.c

···
 	shmem = to_drm_gem_shmem_obj(obj);
 	mutex_init(&shmem->pages_lock);
 	mutex_init(&shmem->vmap_lock);
+	INIT_LIST_HEAD(&shmem->madv_list);
 
 	/*
 	 * Our buffers are kept pinned, so allocating them
···
 	return shmem;
 }
 EXPORT_SYMBOL(drm_gem_shmem_create_with_handle);
+
+/* Update madvise status, returns true if not purged, else
+ * false or -errno.
+ */
+int drm_gem_shmem_madvise(struct drm_gem_object *obj, int madv)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	mutex_lock(&shmem->pages_lock);
+
+	if (shmem->madv >= 0)
+		shmem->madv = madv;
+
+	madv = shmem->madv;
+
+	mutex_unlock(&shmem->pages_lock);
+
+	return (madv >= 0);
+}
+EXPORT_SYMBOL(drm_gem_shmem_madvise);
+
+void drm_gem_shmem_purge_locked(struct drm_gem_object *obj)
+{
+	struct drm_device *dev = obj->dev;
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
+
+	drm_gem_shmem_put_pages_locked(shmem);
+
+	shmem->madv = -1;
+
+	drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
+	drm_gem_free_mmap_offset(obj);
+
+	/* Our goal here is to return as much of the memory as
+	 * is possible back to the system as we are called from OOM.
+	 * To do this we must instruct the shmfs to drop all of its
+	 * backing pages, *now*.
+	 */
+	shmem_truncate_range(file_inode(obj->filp), 0, (loff_t)-1);
+
+	invalidate_mapping_pages(file_inode(obj->filp)->i_mapping,
+			0, (loff_t)-1);
+}
+EXPORT_SYMBOL(drm_gem_shmem_purge_locked);
+
+void drm_gem_shmem_purge(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	mutex_lock(&shmem->pages_lock);
+	drm_gem_shmem_purge_locked(obj);
+	mutex_unlock(&shmem->pages_lock);
+}
+EXPORT_SYMBOL(drm_gem_shmem_purge);
 
 /**
  * drm_gem_shmem_dumb_create - Create a dumb shmem buffer object

include/drm/drm_gem_shmem_helper.h

···
 	 */
 	unsigned int pages_use_count;
 
+	int madv;
+	struct list_head madv_list;
+
 	/**
 	 * @pages_mark_dirty_on_put:
 	 *
···
 void drm_gem_shmem_unpin(struct drm_gem_object *obj);
 void *drm_gem_shmem_vmap(struct drm_gem_object *obj);
 void drm_gem_shmem_vunmap(struct drm_gem_object *obj, void *vaddr);
+
+int drm_gem_shmem_madvise(struct drm_gem_object *obj, int madv);
+
+static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
+{
+	return (shmem->madv > 0) &&
+		!shmem->vmap_use_count && shmem->sgt &&
+		!shmem->base.dma_buf && !shmem->base.import_attach;
+}
+
+void drm_gem_shmem_purge_locked(struct drm_gem_object *obj);
+void drm_gem_shmem_purge(struct drm_gem_object *obj);
 
 struct drm_gem_shmem_object *
 drm_gem_shmem_create_with_handle(struct drm_file *file_priv,