On 09/01/2016 02:40 AM, Andrew Morton wrote:

On Wed, 31 Aug 2016 08:55:49 +0530 Anshuman Khandual [off-list ref] wrote:

quoted

zone_names[] is used to identify any zone given it's index which
can be used in many other places. So moving the definition into
include/linux/mmzone.h for broader access.

...

--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -341,6 +341,23 @@ enum zone_type {
 
 };
 
+static char * const zone_names[__MAX_NR_ZONES] = {
+#ifdef CONFIG_ZONE_DMA
+	 "DMA",
+#endif
+#ifdef CONFIG_ZONE_DMA32
+	 "DMA32",
+#endif
+	 "Normal",
+#ifdef CONFIG_HIGHMEM
+	 "HighMem",
+#endif
+	 "Movable",
+#ifdef CONFIG_ZONE_DEVICE
+	 "Device",
+#endif
+};
+
 #ifndef __GENERATING_BOUNDS_H
 
 struct zone {

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3fbe73a..8e2261c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -207,23 +207,6 @@ int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
 
 EXPORT_SYMBOL(totalram_pages);
 
-static char * const zone_names[MAX_NR_ZONES] = {
-#ifdef CONFIG_ZONE_DMA
-	 "DMA",
-#endif
-#ifdef CONFIG_ZONE_DMA32
-	 "DMA32",
-#endif
-	 "Normal",
-#ifdef CONFIG_HIGHMEM
-	 "HighMem",
-#endif
-	 "Movable",
-#ifdef CONFIG_ZONE_DEVICE
-	 "Device",
-#endif
-};
-
 char * const migratetype_names[MIGRATE_TYPES] = {
 	"Unmovable",
 	"Movable",

This is worrisome.  On some (ancient) compilers, this will produce a
copy of that array into each compilation unit which includes mmzone.h.

On smarter compilers, it will produce a copy of the array in each
compilation unit which *uses* zone_names[].

On even smarter compilers (and linkers!), only one copy of zone_names[]
will exist in vmlinux.

I don't know if gcc is an "even smarter compiler" and I didn't check,
and I didn't check which gcc versions are even smarter.  I'd rather not
have to ;) It is risky.

So, let's just make it non-static and add a declaration into mmzone.h,
please.

I understand your concern, will change it.

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