2 files changed, 53 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index ff71fdcf3345..50c5f42d7a9f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/balloon_compaction.h>
+#include <linux/oom.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -36,6 +37,12 @@
  */
 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
+#define OOM_VBALLOON_DEFAULT_PAGES 256
+#define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
+
+static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
+module_param(oom_pages, int, S_IRUSR | S_IWUSR);
+MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
 
 struct virtio_balloon
 {
@@ -71,6 +78,9 @@ struct virtio_balloon
         /* Memory statistics */
         int need_stats_update;
         struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
+
+        /* To register callback in oom notifier call chain */
+        struct notifier_block nb;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -290,6 +300,38 @@ static void update_balloon_size(struct virtio_balloon *vb)
                       &actual);
 }
 
+/*
+ * virtballoon_oom_notify - release pages when system is under severe
+ *                          memory pressure (called from out_of_memory())
+ * @self : notifier block struct
+ * @dummy: not used
+ * @parm : returned - number of freed pages
+ *
+ * The balancing of memory by use of the virtio balloon should not cause
+ * the termination of processes while there are pages in the balloon.
+ * If virtio balloon manages to release some memory, it will make the
+ * system return and retry the allocation that forced the OOM killer
+ * to run.
+ */
+static int virtballoon_oom_notify(struct notifier_block *self,
+                                  unsigned long dummy, void *parm)
+{
+        struct virtio_balloon *vb;
+        unsigned long *freed;
+        unsigned num_freed_pages;
+
+        vb = container_of(self, struct virtio_balloon, nb);
+        if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+                return NOTIFY_OK;
+
+        freed = parm;
+        num_freed_pages = leak_balloon(vb, oom_pages);
+        update_balloon_size(vb);
+        *freed += num_freed_pages;
+
+        return NOTIFY_OK;
+}
+
 static int balloon(void *_vballoon)
 {
         struct virtio_balloon *vb = _vballoon;
@@ -446,6 +488,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
         if (err)
                 goto out_free_vb;
 
+        vb->nb.notifier_call = virtballoon_oom_notify;
+        vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
+        err = register_oom_notifier(&vb->nb);
+        if (err < 0)
+                goto out_oom_notify;
+
         vb->thread = kthread_run(balloon, vb, "vballoon");
         if (IS_ERR(vb->thread)) {
                 err = PTR_ERR(vb->thread);
@@ -455,6 +503,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
         return 0;
 
 out_del_vqs:
+        unregister_oom_notifier(&vb->nb);
+out_oom_notify:
         vdev->config->del_vqs(vdev);
 out_free_vb:
         kfree(vb);
@@ -479,6 +529,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
 {
         struct virtio_balloon *vb = vdev->priv;
 
+        unregister_oom_notifier(&vb->nb);
         kthread_stop(vb->thread);
         remove_common(vb);
         kfree(vb);
@@ -518,6 +569,7 @@ static int virtballoon_restore(struct virtio_device *vdev)
 static unsigned int features[] = {
         VIRTIO_BALLOON_F_MUST_TELL_HOST,
         VIRTIO_BALLOON_F_STATS_VQ,
+        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index 5e26f61b5df5..be40f7059e93 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -31,6 +31,7 @@
 /* The feature bitmap for virtio balloon */
 #define VIRTIO_BALLOON_F_MUST_TELL_HOST 0 /* Tell before reclaiming pages */
 #define VIRTIO_BALLOON_F_STATS_VQ       1 /* Memory Stats virtqueue */
+#define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12