4 files changed, 48 insertions, 18 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index e60ec54df334..9d02cdb15b23 100644
--- a/arch/arm/Kconfig
+++ b/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
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 186ec6ab334d..a47c879e1304 100644
--- a/include/linux/mmzone.h
+++ b/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 */
diff --git a/mm/mmzone.c b/mm/mmzone.c
index 16ce8b955dcf..f5b7d1760213 100644
--- a/mm/mmzone.c
+++ b/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 */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 66f6130976cb..74d66dba0cbe 100644
--- a/mm/vmstat.c
+++ b/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)