Add MALLCTL_ARENAS_ALL.

Add the MALLCTL_ARENAS_ALL cpp macro as a fixed index for use
in accessing the arena.<i>.{purge,decay,dss} and stats.arenas.<i>.*
mallctls, and deprecate access via the arenas.narenas index (to be
removed in 6.0.0).

include/jemalloc/internal/util.h

@@ -54,6 +54,10 @@
  */
 #define	JEMALLOC_ARG_CONCAT(...) __VA_ARGS__
 
+/* cpp macro definition stringification. */
+#define	STRINGIFY_HELPER(x) #x
+#define	STRINGIFY(x) STRINGIFY_HELPER(x)
+
 /*
  * Silence compiler warnings due to uninitialized values.  This is used
  * wherever the compiler fails to recognize that the variable is never used

include/jemalloc/jemalloc_macros.h.in

@@ -31,6 +31,20 @@
  */
 #define	MALLOCX_ARENA(a)	((((int)(a))+1) << 20)
 
+/*
+ * Use as arena index in "arena.<i>.{purge,decay,dss}" and
+ * "stats.arenas.<i>.*" mallctl interfaces to select all arenas.  This
+ * definition is intentionally specified in raw decimal format to support
+ * cpp-based string concatenation, e.g.
+ *
+ *   #define STRINGIFY_HELPER(x) #x
+ *   #define STRINGIFY(x) STRINGIFY_HELPER(x)
+ *
+ *   mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".purge", NULL, NULL, NULL,
+ *       0);
+ */
+#define	MALLCTL_ARENAS_ALL	4096
+
 #if defined(__cplusplus) && defined(JEMALLOC_USE_CXX_THROW)
 #  define JEMALLOC_CXX_THROW throw()
 #else