---

yaml
---
r: 145179
b: refs/heads/master
c: eb33575
h: refs/heads/master
i:
  145177: 9782d5f
  145175: 2bff2c5
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: e1342f1da06d39b3bbd530e9306347c4438bc6e5
+refs/heads/master: eb33575cf67d3f35fa2510210ef92631266e2465

trunk/arch/arm/Kconfig

@@ -273,6 +273,7 @@ config ARCH_EP93XX
 	select HAVE_CLK
 	select COMMON_CLKDEV
 	select ARCH_REQUIRE_GPIOLIB
+	select ARCH_HAS_HOLES_MEMORYMODEL
 	help
 	  This enables support for the Cirrus EP93xx series of CPUs.
 
@@ -976,10 +977,9 @@ config OABI_COMPAT
 	  UNPREDICTABLE (in fact it can be predicted that it won't work
 	  at all). If in doubt say Y.
 
-config ARCH_FLATMEM_HAS_HOLES
+config ARCH_HAS_HOLES_MEMORYMODEL
 	bool
-	default y
-	depends on FLATMEM
+	default n
 
 # Discontigmem is deprecated
 config ARCH_DISCONTIGMEM_ENABLE

trunk/include/linux/mmzone.h

@@ -1097,6 +1097,32 @@ unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long);
 #define pfn_valid_within(pfn) (1)
 #endif
 
+#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
+/*
+ * pfn_valid() is meant to be able to tell if a given PFN has valid memmap
+ * associated with it or not. In FLATMEM, it is expected that holes always
+ * have valid memmap as long as there is valid PFNs either side of the hole.
+ * In SPARSEMEM, it is assumed that a valid section has a memmap for the
+ * entire section.
+ *
+ * However, an ARM, and maybe other embedded architectures in the future
+ * free memmap backing holes to save memory on the assumption the memmap is
+ * never used. The page_zone linkages are then broken even though pfn_valid()
+ * returns true. A walker of the full memmap must then do this additional
+ * check to ensure the memmap they are looking at is sane by making sure
+ * the zone and PFN linkages are still valid. This is expensive, but walkers
+ * of the full memmap are extremely rare.
+ */
+int memmap_valid_within(unsigned long pfn,
+					struct page *page, struct zone *zone);
+#else
+static inline int memmap_valid_within(unsigned long pfn,
+					struct page *page, struct zone *zone)
+{
+	return 1;
+}
+#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
+
 #endif /* !__GENERATING_BOUNDS.H */
 #endif /* !__ASSEMBLY__ */
 #endif /* _LINUX_MMZONE_H */

trunk/mm/mmzone.c

@@ -6,6 +6,7 @@
 
 
 #include <linux/stddef.h>
+#include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/module.h>
 
@@ -72,3 +73,17 @@ struct zoneref *next_zones_zonelist(struct zoneref *z,
 	*zone = zonelist_zone(z);
 	return z;
 }
+
+#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
+int memmap_valid_within(unsigned long pfn,
+					struct page *page, struct zone *zone)
+{
+	if (page_to_pfn(page) != pfn)
+		return 0;
+
+	if (page_zone(page) != zone)
+		return 0;
+
+	return 1;
+}
+#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */

trunk/mm/vmstat.c

@@ -509,22 +509,11 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
 			continue;
 
 		page = pfn_to_page(pfn);
-#ifdef CONFIG_ARCH_FLATMEM_HAS_HOLES
-		/*
-		 * Ordinarily, memory holes in flatmem still have a valid
-		 * memmap for the PFN range. However, an architecture for
-		 * embedded systems (e.g. ARM) can free up the memmap backing
-		 * holes to save memory on the assumption the memmap is
-		 * never used. The page_zone linkages are then broken even
-		 * though pfn_valid() returns true. Skip the page if the
-		 * linkages are broken. Even if this test passed, the impact
-		 * is that the counters for the movable type are off but
-		 * fragmentation monitoring is likely meaningless on small
-		 * systems.
-		 */
-		if (page_zone(page) != zone)
+
+		/* Watch for unexpected holes punched in the memmap */
+		if (!memmap_valid_within(pfn, page, zone))
 			continue;
-#endif
+
 		mtype = get_pageblock_migratetype(page);
 
 		if (mtype < MIGRATE_TYPES)