path: root/drivers/virtio/virtio_balloon.c
diff options
authorAmit Shah <amit.shah@redhat.com>2011-12-22 16:58:35 +0530
committerRusty Russell <rusty@rustcorp.com.au>2012-01-12 15:44:47 +1030
commite562966dbaf49e7804097cd991e5d3a8934fc148 (patch)
tree08d1b0bda7ddf76d9cce26c1a340ac86de541033 /drivers/virtio/virtio_balloon.c
parentbe91c33dd15eff6b0dffc60cee4c8042e75493d2 (diff)
virtio: balloon: Add freeze, restore handlers to support S4
Handling balloon hibernate / restore is tricky. If the balloon was inflated before going into the hibernation state, upon resume, the host will not have any memory of that. Any pages that were passed on to the host earlier would most likely be invalid, and the host will have to re-balloon to the previous value to get in the pre-hibernate state. So the only sane thing for the guest to do here is to discard all the pages that were put in the balloon. When to discard the pages is the next question. One solution is to deflate the balloon just before writing the image to the disk (in the freeze() PM callback). However, asking for pages from the host just to discard them immediately after seems wasteful of resources. Hence, it makes sense to do this by just fudging our counters soon after wakeup. This means we don't deflate the balloon before sleep, and also don't put unnecessary pressure on the host. This also helps in the thaw case: if the freeze fails for whatever reason, the balloon should continue to remain in the inflated state. This was tested by issuing 'swapoff -a' and trying to go into the S4 state. That fails, and the balloon stays inflated, as expected. Both the host and the guest are happy. Finally, in the restore() callback, we empty the list of pages that were previously given off to the host, add the appropriate number of pages to the totalram_pages counter, reset the num_pages counter to 0, and all is fine. As a last step, delete the vqs on the freeze callback to prepare for hibernation, and re-create them in the restore and thaw callbacks to resume normal operation. The kthread doesn't race with any operations here, since it's frozen before the freeze() call and is thawed after the thaw() and restore() callbacks, so we're safe with that. Signed-off-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'drivers/virtio/virtio_balloon.c')
1 files changed, 47 insertions, 0 deletions
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 3368cb6ef19..95aeedf198f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -364,6 +364,48 @@ static void __devexit virtballoon_remove(struct virtio_device *vdev)
+#ifdef CONFIG_PM
+static int virtballoon_freeze(struct virtio_device *vdev)
+ /*
+ * The kthread is already frozen by the PM core before this
+ * function is called.
+ */
+ /* Ensure we don't get any more requests from the host */
+ vdev->config->reset(vdev);
+ vdev->config->del_vqs(vdev);
+ return 0;
+static int virtballoon_thaw(struct virtio_device *vdev)
+ return init_vqs(vdev->priv);
+static int virtballoon_restore(struct virtio_device *vdev)
+ struct virtio_balloon *vb = vdev->priv;
+ struct page *page, *page2;
+ /* We're starting from a clean slate */
+ vb->num_pages = 0;
+ /*
+ * If a request wasn't complete at the time of freezing, this
+ * could have been set.
+ */
+ vb->need_stats_update = 0;
+ /* We don't have these pages in the balloon anymore! */
+ list_for_each_entry_safe(page, page2, &vb->pages, lru) {
+ list_del(&page->lru);
+ totalram_pages++;
+ }
+ return init_vqs(vdev->priv);
static unsigned int features[] = {
@@ -378,6 +420,11 @@ static struct virtio_driver virtio_balloon_driver = {
.probe = virtballoon_probe,
.remove = __devexit_p(virtballoon_remove),
.config_changed = virtballoon_changed,
+#ifdef CONFIG_PM
+ .freeze = virtballoon_freeze,
+ .restore = virtballoon_restore,
+ .thaw = virtballoon_thaw,
static int __init init(void)