quoted

+/*
+ * VIRTIO_BALLOON_PFNS_LIMIT is used to limit the size of page bitmap
+ * to prevent a very large page bitmap, there are two reasons for this:
+ * 1) to save memory.
+ * 2) allocate a large bitmap may fail.
+ *
+ * The actual limit of pfn is determined by:
+ * pfn_limit = min(max_pfn, VIRTIO_BALLOON_PFNS_LIMIT);
+ *
+ * If system has more pages than VIRTIO_BALLOON_PFNS_LIMIT, we will
+scan
+ * the page list and send the PFNs with several times. To reduce the
+ * overhead of scanning the page list. VIRTIO_BALLOON_PFNS_LIMIT
+should
+ * be set with a value which can cover most cases.
+ */
+#define VIRTIO_BALLOON_PFNS_LIMIT ((32 * (1ULL << 30)) >>

PAGE_SHIFT)

quoted

+/* 32GB */
+
 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");

+extern unsigned long get_max_pfn(void);
+

Please just include the correct header. No need for this hackery.

Will change. Thanks!

Liang