[RFC v2 12/13] vduse: Add memory shrinker to reclaim bounce pages

[Xie Yongji <xieyongji@xxxxxxxxxxxxx>]

Add a shrinker to reclaim several pages used by bounce buffer
in order to avoid memory pressures.

Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 51 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index c29b24a7e7e9..1bc2e627c476 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -1142,6 +1142,43 @@ static long vduse_ioctl(struct file *file, unsigned int cmd,
 	return ret;
 }
 
+static unsigned long vduse_shrink_scan(struct shrinker *shrinker,
+					struct shrink_control *sc)
+{
+	unsigned long freed = 0;
+	struct vduse_dev *dev;
+
+	if (!mutex_trylock(&vduse_lock))
+		return SHRINK_STOP;
+
+	list_for_each_entry(dev, &vduse_devs, list) {
+		if (!dev->domain)
+			continue;
+
+		freed = vduse_domain_reclaim(dev->domain);
+		if (!freed)
+			continue;
+
+		list_move_tail(&dev->list, &vduse_devs);
+		break;
+	}
+	mutex_unlock(&vduse_lock);
+
+	return freed ? freed : SHRINK_STOP;
+}
+
+static unsigned long vduse_shrink_count(struct shrinker *shrink,
+					struct shrink_control *sc)
+{
+	return percpu_counter_read_positive(&vduse_total_bounce_pages);
+}
+
+static struct shrinker vduse_bounce_pages_shrinker = {
+	.count_objects = vduse_shrink_count,
+	.scan_objects = vduse_shrink_scan,
+	.seeks = DEFAULT_SEEKS,
+};
+
 static const struct file_operations vduse_fops = {
 	.owner		= THIS_MODULE,
 	.unlocked_ioctl	= vduse_ioctl,
@@ -1292,12 +1329,24 @@ static int vduse_init(void)
 	if (ret)
 		goto err_irqfd;
 
+	ret = vduse_domain_init();
+	if (ret)
+		goto err_domain;
+
+	ret = register_shrinker(&vduse_bounce_pages_shrinker);
+	if (ret)
+		goto err_shrinker;
+
 	ret = vduse_parentdev_init();
 	if (ret)
 		goto err_parentdev;
 
 	return 0;
 err_parentdev:
+	unregister_shrinker(&vduse_bounce_pages_shrinker);
+err_shrinker:
+	vduse_domain_exit();
+err_domain:
 	vduse_virqfd_exit();
 err_irqfd:
 	destroy_workqueue(vduse_vdpa_wq);
@@ -1309,8 +1358,10 @@ module_init(vduse_init);
 
 static void vduse_exit(void)
 {
+	unregister_shrinker(&vduse_bounce_pages_shrinker);
 	misc_deregister(&vduse_misc);
 	destroy_workqueue(vduse_vdpa_wq);
+	vduse_domain_exit();
 	vduse_virqfd_exit();
 	vduse_parentdev_exit();
 }
-- 
2.11.0