mm/migrate: de-duplicate migrate_reason strings

In order to remove the need to manually keep three different files in
synch, provide a common definition of the mapping between enum
migrate_reason, and the associated strings for each enum item.

1. Use the tracing system's mapping of enums to strings, by redefining
   and reusing the MIGRATE_REASON and supporting macros, and using that
   to populate the string array in mm/debug.c.

2. Move enum migrate_reason to migrate_mode.h. This is not strictly
   necessary for this patch, but migrate mode and migrate reason go
   together, so this will slightly clarify things.

Link: https://lkml.kernel.org/r/20210922041755.141817-2-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Weizhao Ouyang <o451686892@gmail.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/migrate.h

@@ -19,24 +19,7 @@ struct migration_target_control;
  */
 #define MIGRATEPAGE_SUCCESS		0
 
-/*
- * Keep sync with:
- * - macro MIGRATE_REASON in include/trace/events/migrate.h
- * - migrate_reason_names[MR_TYPES] in mm/debug.c
- */
-enum migrate_reason {
-	MR_COMPACTION,
-	MR_MEMORY_FAILURE,
-	MR_MEMORY_HOTPLUG,
-	MR_SYSCALL,		/* also applies to cpusets */
-	MR_MEMPOLICY_MBIND,
-	MR_NUMA_MISPLACED,
-	MR_CONTIG_RANGE,
-	MR_LONGTERM_PIN,
-	MR_DEMOTION,
-	MR_TYPES
-};
-
+/* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
 #ifdef CONFIG_MIGRATION

include/linux/migrate_mode.h

@@ -19,4 +19,17 @@ enum migrate_mode {
 	MIGRATE_SYNC_NO_COPY,
 };
 
+enum migrate_reason {
+	MR_COMPACTION,
+	MR_MEMORY_FAILURE,
+	MR_MEMORY_HOTPLUG,
+	MR_SYSCALL,		/* also applies to cpusets */
+	MR_MEMPOLICY_MBIND,
+	MR_NUMA_MISPLACED,
+	MR_CONTIG_RANGE,
+	MR_LONGTERM_PIN,
+	MR_DEMOTION,
+	MR_TYPES
+};
+
 #endif		/* MIGRATE_MODE_H_INCLUDED */

mm/debug.c

@@ -16,17 +16,19 @@
 #include <linux/ctype.h>
 
 #include "internal.h"
+#include <trace/events/migrate.h>
+
+/*
+ * Define EM() and EMe() so that MIGRATE_REASON from trace/events/migrate.h can
+ * be used to populate migrate_reason_names[].
+ */
+#undef EM
+#undef EMe
+#define EM(a, b)	b,
+#define EMe(a, b)	b
 
 const char *migrate_reason_names[MR_TYPES] = {
-	"compaction",
-	"memory_failure",
-	"memory_hotplug",
-	"syscall_or_cpuset",
-	"mempolicy_mbind",
-	"numa_misplaced",
-	"contig_range",
-	"longterm_pin",
-	"demotion",
+	MIGRATE_REASON
 };
 
 const struct trace_print_flags pageflag_names[] = {