balloon: fix max voluntary size in bytes not pages

The maximum voluntary inflation size was previously specified in bytes,
but used as if it were a number of pages. Fix this by directly
specifying the maximum voluntary inflation size as a number of 4K pages.

Author: hcsch

src/drivers/balloon/mod.rs

@@ -33,10 +33,14 @@ pub mod oom;
 #[cfg(feature = "pci")]
 mod pci;
 
-const BALLOON_PAGE_SIZE: usize = 4096;
+const KIBI: u32 = 1024;
+const MEBI: u32 = 1024 * KIBI;
+const GIBI: u32 = 1024 * MEBI;
+
+const BALLOON_PAGE_SIZE: usize = 4 * KIBI as usize;
 
 const VOLUNTARY_INFLATE_INTERVAL_MICROS: u64 = 1_000_000;
-const VOLUNTARY_INFLATE_MAX_SIZE_BYTES: u32 = 1 << 31; // 2 GiB
+const VOLUNTARY_INFLATE_MAX_NUM_PAGES: u32 = 2 * GIBI / BALLOON_PAGE_SIZE as u32;
 
 // TODO: prevent possible deflate of not yet acknowledged inflated pages. See VIRTIO v1.2 5.5.6.1
 
@@ -362,7 +366,7 @@ impl VirtioBalloonDriver {
 			debug!("<balloon> Voluntarily inflating balloon as much as we can");
 			let num_inflated = self.inflate(
 				&mut ALLOCATOR.inner().lock(),
-				VOLUNTARY_INFLATE_MAX_SIZE_BYTES,
+				VOLUNTARY_INFLATE_MAX_NUM_PAGES,
 				true,
 			);
 			debug!(