[RFC PATCH 04/15] mm: prevent pageblock size being larger than section size.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

Only physical pages from a section can be guaranteed to be contiguous
and so far a pageblock can only group contiguous physical pages by
design. Set pageblock_order properly to prevent pageblock going beyond
section size.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/pageblock-flags.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 973fd731a520..4277b4267767 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -44,8 +44,11 @@ extern unsigned int pageblock_order;
 
 #else /* CONFIG_HUGETLB_PAGE */
 
-/* If huge pages are not used, group by MAX_ORDER_NR_PAGES */
-#define pageblock_order		(MAX_ORDER-1)
+/*
+ * If huge pages are not used, group by MAX_ORDER_NR_PAGES or
+ * PAGES_PER_SECTION when MAX_ORDER_NR_PAGES is larger.
+ */
+#define pageblock_order		(min(PFN_SECTION_SHIFT, MAX_ORDER-1))
 
 #endif /* CONFIG_HUGETLB_PAGE */
 
-- 
2.30.2