[PATCH 5.6 034/177] Revert "virtio-balloon: Revert "virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM""

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

This reverts commit 37681282be8e89ae8baf26753bf489837d74e08e which is
commit 835a6a649d0dd1b1f46759eb60fff2f63ed253a7 upstream.

Jiri and David agree that it is not needed in the 5.6.y tree, so revert
it.

Reported-by: Jiri Slaby <jslaby@xxxxxxx>
Reported-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_balloon.c |  107 ++++++++++++++++------------------------
 1 file changed, 44 insertions(+), 63 deletions(-)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/balloon_compaction.h>
+#include <linux/oom.h>
 #include <linux/wait.h>
 #include <linux/mm.h>
 #include <linux/mount.h>
@@ -27,7 +28,9 @@
  */
 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
-#define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
+/* Maximum number of (4k) pages to deflate on OOM notifications. */
+#define VIRTIO_BALLOON_OOM_NR_PAGES 256
+#define VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY 80
 
 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
 					     __GFP_NOMEMALLOC)
@@ -112,8 +115,11 @@ struct virtio_balloon {
 	/* Memory statistics */
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 
-	/* To register a shrinker to shrink memory upon memory pressure */
+	/* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */
 	struct shrinker shrinker;
+
+	/* OOM notifier to deflate on OOM - VIRTIO_BALLOON_F_DEFLATE_ON_OOM */
+	struct notifier_block oom_nb;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -788,50 +794,13 @@ static unsigned long shrink_free_pages(s
 	return blocks_freed * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
 }
 
-static unsigned long leak_balloon_pages(struct virtio_balloon *vb,
-                                          unsigned long pages_to_free)
-{
-	return leak_balloon(vb, pages_to_free * VIRTIO_BALLOON_PAGES_PER_PAGE) /
-		VIRTIO_BALLOON_PAGES_PER_PAGE;
-}
-
-static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
-					  unsigned long pages_to_free)
-{
-	unsigned long pages_freed = 0;
-
-	/*
-	 * One invocation of leak_balloon can deflate at most
-	 * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
-	 * multiple times to deflate pages till reaching pages_to_free.
-	 */
-	while (vb->num_pages && pages_freed < pages_to_free)
-		pages_freed += leak_balloon_pages(vb,
-						  pages_to_free - pages_freed);
-
-	update_balloon_size(vb);
-
-	return pages_freed;
-}
-
 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 						  struct shrink_control *sc)
 {
-	unsigned long pages_to_free, pages_freed = 0;
 	struct virtio_balloon *vb = container_of(shrinker,
 					struct virtio_balloon, shrinker);
 
-	pages_to_free = sc->nr_to_scan;
-
-	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
-		pages_freed = shrink_free_pages(vb, pages_to_free);
-
-	if (pages_freed >= pages_to_free)
-		return pages_freed;
-
-	pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
-
-	return pages_freed;
+	return shrink_free_pages(vb, sc->nr_to_scan);
 }
 
 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
@@ -839,26 +808,22 @@ static unsigned long virtio_balloon_shri
 {
 	struct virtio_balloon *vb = container_of(shrinker,
 					struct virtio_balloon, shrinker);
-	unsigned long count;
-
-	count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
-	count += vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
 
-	return count;
+	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
 }
 
-static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
+static int virtio_balloon_oom_notify(struct notifier_block *nb,
+				     unsigned long dummy, void *parm)
 {
-	unregister_shrinker(&vb->shrinker);
-}
+	struct virtio_balloon *vb = container_of(nb,
+						 struct virtio_balloon, oom_nb);
+	unsigned long *freed = parm;
 
-static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
-{
-	vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
-	vb->shrinker.count_objects = virtio_balloon_shrinker_count;
-	vb->shrinker.seeks = DEFAULT_SEEKS;
+	*freed += leak_balloon(vb, VIRTIO_BALLOON_OOM_NR_PAGES) /
+		  VIRTIO_BALLOON_PAGES_PER_PAGE;
+	update_balloon_size(vb);
 
-	return register_shrinker(&vb->shrinker);
+	return NOTIFY_OK;
 }
 
 static int virtballoon_probe(struct virtio_device *vdev)
@@ -935,22 +900,35 @@ static int virtballoon_probe(struct virt
 			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 				      poison_val, &poison_val);
 		}
-	}
-	/*
-	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
-	 * shrinker needs to be registered to relieve memory pressure.
-	 */
-	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
-		err = virtio_balloon_register_shrinker(vb);
+
+		/*
+		 * We're allowed to reuse any free pages, even if they are
+		 * still to be processed by the host.
+		 */
+		vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
+		vb->shrinker.count_objects = virtio_balloon_shrinker_count;
+		vb->shrinker.seeks = DEFAULT_SEEKS;
+		err = register_shrinker(&vb->shrinker);
 		if (err)
 			goto out_del_balloon_wq;
 	}
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
+		vb->oom_nb.notifier_call = virtio_balloon_oom_notify;
+		vb->oom_nb.priority = VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY;
+		err = register_oom_notifier(&vb->oom_nb);
+		if (err < 0)
+			goto out_unregister_shrinker;
+	}
+
 	virtio_device_ready(vdev);
 
 	if (towards_target(vb))
 		virtballoon_changed(vdev);
 	return 0;
 
+out_unregister_shrinker:
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		unregister_shrinker(&vb->shrinker);
 out_del_balloon_wq:
 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 		destroy_workqueue(vb->balloon_wq);
@@ -989,8 +967,11 @@ static void virtballoon_remove(struct vi
 {
 	struct virtio_balloon *vb = vdev->priv;
 
-	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
-		virtio_balloon_unregister_shrinker(vb);
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		unregister_oom_notifier(&vb->oom_nb);
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		unregister_shrinker(&vb->shrinker);
+
 	spin_lock_irq(&vb->stop_update_lock);
 	vb->stop_update = true;
 	spin_unlock_irq(&vb->stop_update_lock);