xen/balloon: don't use PV mode extra memory for zone device allocations

When running as a Xen PV guest use the extra memory (memory which isn't
allocated for the guest at boot time) only for ballooning purposes and
not for zone device allocations. This will remove some code without any
lack of functionality.

While at it move some code to get rid of another #ifdef.

Remove a comment which is stale since some time now.

Signed-off-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220407093857.1485-1-jgross@suse.com
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Author: jgross1

drivers/xen/balloon.c

@@ -689,29 +689,34 @@ void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL(xen_free_ballooned_pages);
 
-#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC)
-static void __init balloon_add_region(unsigned long start_pfn,
-				      unsigned long pages)
+static void __init balloon_add_regions(void)
 {
+#if defined(CONFIG_XEN_PV)
+	unsigned long start_pfn, pages;
 	unsigned long pfn, extra_pfn_end;
+	unsigned int i;
 
-	/*
-	 * If the amount of usable memory has been limited (e.g., with
-	 * the 'mem' command line parameter), don't add pages beyond
-	 * this limit.
-	 */
-	extra_pfn_end = min(max_pfn, start_pfn + pages);
+	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
+		pages = xen_extra_mem[i].n_pfns;
+		if (!pages)
+			continue;
 
-	for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
-		/* totalram_pages and totalhigh_pages do not
-		   include the boot-time balloon extension, so
-		   don't subtract from it. */
-		balloon_append(pfn_to_page(pfn));
-	}
+		start_pfn = xen_extra_mem[i].start_pfn;
 
-	balloon_stats.total_pages += extra_pfn_end - start_pfn;
-}
+		/*
+		 * If the amount of usable memory has been limited (e.g., with
+		 * the 'mem' command line parameter), don't add pages beyond
+		 * this limit.
+		 */
+		extra_pfn_end = min(max_pfn, start_pfn + pages);
+
+		for (pfn = start_pfn; pfn < extra_pfn_end; pfn++)
+			balloon_append(pfn_to_page(pfn));
+
+		balloon_stats.total_pages += extra_pfn_end - start_pfn;
+	}
 #endif
+}
 
 static int __init balloon_init(void)
 {
@@ -745,20 +750,7 @@ static int __init balloon_init(void)
 	register_sysctl_table(xen_root);
 #endif
 
-#if defined(CONFIG_XEN_PV) && !defined(CONFIG_XEN_UNPOPULATED_ALLOC)
-	{
-		int i;
-
-		/*
-		 * Initialize the balloon with pages from the extra memory
-		 * regions (see arch/x86/xen/setup.c).
-		 */
-		for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
-			if (xen_extra_mem[i].n_pfns)
-				balloon_add_region(xen_extra_mem[i].start_pfn,
-						   xen_extra_mem[i].n_pfns);
-	}
-#endif
+	balloon_add_regions();
 
 	task = kthread_run(balloon_thread, NULL, "xen-balloon");
 	if (IS_ERR(task)) {

drivers/xen/unpopulated-alloc.c

@@ -230,39 +230,6 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL(xen_free_unpopulated_pages);
 
-#ifdef CONFIG_XEN_PV
-static int __init init(void)
-{
-	unsigned int i;
-
-	if (!xen_domain())
-		return -ENODEV;
-
-	if (!xen_pv_domain())
-		return 0;
-
-	/*
-	 * Initialize with pages from the extra memory regions (see
-	 * arch/x86/xen/setup.c).
-	 */
-	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
-		unsigned int j;
-
-		for (j = 0; j < xen_extra_mem[i].n_pfns; j++) {
-			struct page *pg =
-				pfn_to_page(xen_extra_mem[i].start_pfn + j);
-
-			pg->zone_device_data = page_list;
-			page_list = pg;
-			list_count++;
-		}
-	}
-
-	return 0;
-}
-subsys_initcall(init);
-#endif
-
 static int __init unpopulated_init(void)
 {
 	int ret;