linux-kernel - [BUG] [PATCH v2] Make setup_zone_migrate_reserve() aware of overlapping nodes

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Date:	Wed, 20 Aug 2008 14:55:52 -0500
From:	Adam Litke <agl@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	nacc <nacc@...ux.vnet.ibm.com>, mel@....ul.ie,
	apw <apw@...dowen.org>, agl <agl@...ux.vnet.ibm.com>
Subject: [BUG] [PATCH v2] Make setup_zone_migrate_reserve() aware of
	overlapping nodes

    Changes since V1
     - Fix build for !NUMA
     - Add VM_BUG_ON() to catch this problem at the source
    
    I have gotten to the root cause of the hugetlb badness I reported back on
    August 15th.  My system has the following memory topology (note the
    overlapping node):
    
            Node 0 Memory: 0x8000000-0x44000000
            Node 1 Memory: 0x0-0x8000000 0x44000000-0x80000000
    
    setup_zone_migrate_reserve() scans the address range 0x0-0x8000000 looking
    for a pageblock to move onto the MIGRATE_RESERVE list.  Finding no
    candidates, it happily continues the scan into 0x8000000-0x44000000.  When
    a pageblock is found, the pages are moved to the MIGRATE_RESERVE list on
    the wrong zone.  Oops.
    
    (Andrew: once the proper fix is agreed upon, this should also be a
    candidate for -stable.)
    
    setup_zone_migrate_reserve() should skip pageblocks in overlapping nodes.
    
    Signed-off-by: Adam Litke <agl@...ibm.com>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index af982f7..feb7916 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -694,6 +694,9 @@ static 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;
@@ -2516,6 +2519,10 @@ static void setup_zone_migrate_reserve(struct zone *zone)
 			continue;
 		page = pfn_to_page(pfn);
 
+		/* Watch out for overlapping nodes */
+		if (page_to_nid(page) != zone_to_nid(zone))
+			continue;
+
 		/* Blocks with reserved pages will never free, skip them. */
 		if (PageReserved(page))
 			continue;

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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