diff options
authorMel Gorman <>2012-12-06 19:01:14 +0000
committerLinus Torvalds <>2012-12-06 11:17:33 -0800
commit60177d31d215bc2b4c5a7aa6f742800e04fa0a92 (patch)
parent04c5decdc0aecde43bf44860484f26ee0691335f (diff)
mm: compaction: validate pfn range passed to isolate_freepages_block
Commit 0bf380bc70ec ("mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration") added a check for pfn_valid() when isolating pages for migration as the scanner does not necessarily start pageblock-aligned. Since commit c89511ab2f8f ("mm: compaction: Restart compaction from near where it left off"), the free scanner has the same problem. This patch makes sure that the pfn range passed to isolate_freepages_block() is within the same block so that pfn_valid() checks are unnecessary. In answer to Henrik's wondering why others have not reported this: reproducing this requires a large enough hole with the right aligment to have compaction walk into a PFN range with no memmap. Size and alignment depends in the memory model - 4M for FLATMEM and 128M for SPARSEMEM on x86. It needs a "lucky" machine. Reported-by: Henrik Rydberg <> Signed-off-by: Mel Gorman <> Signed-off-by: Linus Torvalds <>
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 9eef55838fca..694eaabaaebd 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -713,7 +713,15 @@ static void isolate_freepages(struct zone *zone,
/* Found a block suitable for isolating free pages from */
isolated = 0;
- end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
+ /*
+ * As pfn may not start aligned, pfn+pageblock_nr_page
+ * may cross a MAX_ORDER_NR_PAGES boundary and miss
+ * a pfn_valid check. Ensure isolate_freepages_block()
+ * only scans within a pageblock
+ */
+ end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
+ end_pfn = min(end_pfn, zone_end_pfn);
isolated = isolate_freepages_block(cc, pfn, end_pfn,
freelist, false);
nr_freepages += isolated;