[RFC PATCH v3 09/31] page_alloc: in move_freepages(), skip pages instead of VM_BUG on node differences.

[Cody P Schafer <cody@linux.vnet.ibm.com>]

With dynamic numa, pages are going to be gradully moved from one node to
another, causing the page ranges that move_freepages() examines to
contain pages that actually belong to another node.

When dynamic numa is enabled, we skip these pages instead of VM_BUGing
out on them.

This additionally moves the VM_BUG_ON() (which detects a change in node)
so that it follows the pfn_valid_within() check.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 mm/page_alloc.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 739b405..657f773 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -958,6 +958,7 @@ int move_freepages(struct zone *zone,
 	struct page *page;
 	unsigned long order;
 	int pages_moved = 0;
+	int zone_nid = zone_to_nid(zone);
 
 #ifndef CONFIG_HOLES_IN_ZONE
 	/*
@@ -971,14 +972,24 @@ int move_freepages(struct zone *zone,
 #endif
 
 	for (page = start_page; page <= end_page;) {
-		/* Make sure we are not inadvertently changing nodes */
-		VM_BUG_ON(page_to_nid(page) != zone_to_nid(zone));
-
 		if (!pfn_valid_within(page_to_pfn(page))) {
 			page++;
 			continue;
 		}
 
+		if (page_to_nid(page) != zone_nid) {
+#ifndef CONFIG_DYNAMIC_NUMA
+			/*
+			 * In the normal case (without Dynamic NUMA), all pages
+			 * in a pageblock should belong to the same zone (and
+			 * as a result all have the same nid).
+			 */
+			VM_BUG_ON(page_to_nid(page) != zone_nid);
+#endif
+			page++;
+			continue;
+		}
+
 		if (!PageBuddy(page)) {
 			page++;
 			continue;
-- 
1.8.2.2