[RFC IDEA v2 6/6] drivers/virtio/virtio_balloon: integrate ACMA and ballooning

[SeongJae Park <sj@kernel.org>]

Let the host effectively inflate the balloon in access/contiguity-aware
way when the guest kernel is compiled with specific kernel config.  When
the config is enabled and the host requests balloon size change,
virtio-balloon adjusts ACMA's max-mem parameter instead of allocating
guest pages and put it into the balloon.  As a result, the host can use
the requested amount of guest memory, so from the host's perspective,
the ballooning just works, but in transparent and
access/contiguity-aware way.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 drivers/virtio/virtio_balloon.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 1f5b3dd31fcf..a954d75789ae 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -472,6 +472,32 @@ static void virtballoon_changed(struct virtio_device *vdev)
 	struct virtio_balloon *vb = vdev->priv;
 	unsigned long flags;
 
+#ifdef CONFIG_ACMA_BALLOON
+	s64 target;
+	u32 num_pages;
+
+
+	/* Legacy balloon config space is LE, unlike all other devices. */
+	virtio_cread_le(vb->vdev, struct virtio_balloon_config, num_pages,
+			&num_pages);
+
+	/*
+	 * Aligned up to guest page size to avoid inflating and deflating
+	 * balloon endlessly.
+	 */
+	target = ALIGN(num_pages, VIRTIO_BALLOON_PAGES_PER_PAGE);
+
+	/*
+	 * If the given new max mem size is larger than current acma's max mem
+	 * size, same to normal max mem adjustment.
+	 * If the given new max mem size is smaller than current acma's max mem
+	 * size, strong aggressiveness is applied while memory for meeting the
+	 * new max mem is met is stolen.
+	 */
+	acma_set_max_mem_aggressive(totalram_pages() - target);
+	return;
+#endif
+
 	spin_lock_irqsave(&vb->stop_update_lock, flags);
 	if (!vb->stop_update) {
 		start_update_balloon_size(vb);
-- 
2.39.2