virtio: Fix GFP flags passed from the virtio balloon driver

The virtio balloon driver can dig into the reservation pools of the OS
to satisfy a balloon request.  This is not advisable and other balloon
drivers (drivers/xen/balloon.c) avoid this as well.

The patch also adds changes to avoid printing a warning if allocation
fails, since we retry after sometime anyway.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: kvm <kvm@vger.kernel.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/virtio/virtio_balloon.c

@@ -103,7 +103,8 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
 	num = min(num, ARRAY_SIZE(vb->pfns));
 
 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
-		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
+		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
+					__GFP_NOMEMALLOC | __GFP_NOWARN);
 		if (!page) {
 			if (printk_ratelimit())
 				dev_printk(KERN_INFO, &vb->vdev->dev,