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.
Change-Id: I5de91fc8d9792cb339b87fe9ef058143cde5995a
Reported-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 60177d31d215bc2b4c5a7aa6f742800e04fa0a92
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
diff --git a/mm/compaction.c b/mm/compaction.c
index 195e9be..b3acc10 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -710,7 +710,15 @@
/* 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;