virtio-balloon: Revert "virtio-balloon: Switch back to OOM handler for...

virtio-balloon: Revert "virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM"

This reverts commit 5a6b4cc5.

It has been queued properly in the akpm tree, this version is just
creating conflicts.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_balloon.c

@@ -14,7 +14,6 @@
 #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>
@@ -28,9 +27,7 @@
  */
 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
-/* 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 VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
 
 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
 					     __GFP_NOMEMALLOC)
@@ -115,11 +112,8 @@ struct virtio_balloon {
 	/* Memory statistics */
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 
-	/* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */
+	/* To register a shrinker to shrink memory upon memory pressure */
 	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[] = {
@@ -794,13 +788,50 @@ static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 	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);
 
-	return shrink_free_pages(vb, sc->nr_to_scan);
+	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;
 }
 
 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
@@ -808,22 +839,26 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 {
 	struct virtio_balloon *vb = container_of(shrinker,
 					struct virtio_balloon, shrinker);
+	unsigned long count;
 
-	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
+	count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
+	count += vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
+
+	return count;
 }
 
-static int virtio_balloon_oom_notify(struct notifier_block *nb,
-				     unsigned long dummy, void *parm)
+static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 {
-	struct virtio_balloon *vb = container_of(nb,
-						 struct virtio_balloon, oom_nb);
-	unsigned long *freed = parm;
+	unregister_shrinker(&vb->shrinker);
+}
 
-	*freed += leak_balloon(vb, VIRTIO_BALLOON_OOM_NR_PAGES) /
-		  VIRTIO_BALLOON_PAGES_PER_PAGE;
-	update_balloon_size(vb);
+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;
 
-	return NOTIFY_OK;
+	return register_shrinker(&vb->shrinker);
 }
 
 static int virtballoon_probe(struct virtio_device *vdev)
@@ -900,35 +935,22 @@ static int virtballoon_probe(struct virtio_device *vdev)
 			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 				      poison_val, &poison_val);
 		}
-
+	}
 	/*
-		 * We're allowed to reuse any free pages, even if they are
-		 * still to be processed by the host.
+	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
+	 * shrinker needs to be registered to relieve memory pressure.
 	 */
-		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 (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
+		err = virtio_balloon_register_shrinker(vb);
 		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);
@@ -967,11 +989,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;
 
-	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);
-
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		virtio_balloon_unregister_shrinker(vb);
 	spin_lock_irq(&vb->stop_update_lock);
 	vb->stop_update = true;
 	spin_unlock_irq(&vb->stop_update_lock);