Define MADV_FREE on our own when needed.

On x86 Linux, we define our own MADV_FREE if madvise(2) is available, but no
MADV_FREE is detected.  This allows the feature to be built in and enabled with
runtime detection.

configure.ac

@@ -1824,6 +1824,15 @@ if test "x${je_cv_madvise}" = "xyes" ; then
 ], [je_cv_madv_free])
   if test "x${je_cv_madv_free}" = "xyes" ; then
     AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
+  elif test "x${je_cv_madvise}" = "xyes" ; then
+    case "${host_cpu}" in i686|x86_64)
+        case "${host}" in *-*-linux*)
+            AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
+            AC_DEFINE([JEMALLOC_DEFINE_MADVISE_FREE], [ ])
+	    ;;
+        esac
+        ;;
+    esac
   fi
 
   dnl Check for madvise(..., MADV_DONTNEED).

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -285,6 +285,9 @@
 #undef JEMALLOC_PURGE_MADVISE_DONTNEED
 #undef JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS
 
+/* Defined if madvise(2) is available but MADV_FREE is not (x86 Linux only). */
+#undef JEMALLOC_DEFINE_MADVISE_FREE
+
 /*
  * Defined if transparent huge pages (THPs) are supported via the
  * MADV_[NO]HUGEPAGE arguments to madvise(2), and THP support is enabled.

include/jemalloc/internal/jemalloc_preamble.h.in

@@ -47,6 +47,10 @@
 #endif
 #include "jemalloc/internal/hooks.h"
 
+#ifdef JEMALLOC_DEFINE_MADVISE_FREE
+#  define JEMALLOC_MADV_FREE 8
+#endif
+
 static const bool config_debug =
 #ifdef JEMALLOC_DEBUG
     true

src/pages.c

@@ -269,7 +269,13 @@ pages_purge_lazy(void *addr, size_t size) {
 	VirtualAlloc(addr, size, MEM_RESET, PAGE_READWRITE);
 	return false;
 #elif defined(JEMALLOC_PURGE_MADVISE_FREE)
-	return (madvise(addr, size, MADV_FREE) != 0);
+	return (madvise(addr, size,
+#  ifdef MADV_FREE
+	    MADV_FREE
+#  else
+	    JEMALLOC_MADV_FREE
+#  endif
+	    ) != 0);
 #elif defined(JEMALLOC_PURGE_MADVISE_DONTNEED) && \
     !defined(JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS)
 	return (madvise(addr, size, MADV_DONTNEED) != 0);