Refactor madvise(2) configuration.

Add feature tests for the MADV_FREE and MADV_DONTNEED flags to
madvise(2), so that MADV_FREE is detected and used for Linux kernel
versions 4.5 and newer.  Refactor pages_purge() so that on systems which
support both flags, MADV_FREE is preferred over MADV_DONTNEED.

This resolves #387.

3 files changed, 39 insertions, 30 deletions

diff --git a/configure.ac b/configure.ac
index 72021e0..15897be 100644
--- a/configure.ac
+++ b/configure.ac
@@ -354,7 +354,6 @@ maps_coalesce="1"
 case "${host}" in
   *-*-darwin* | *-*-ios*)
 	abi="macho"
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	RPATH=""
 	LD_PRELOAD_VAR="DYLD_INSERT_LIBRARIES"
 	so="dylib"
@@ -367,21 +366,17 @@ case "${host}" in
   *-*-freebsd*)
 	abi="elf"
 	AC_DEFINE([JEMALLOC_SYSCTL_VM_OVERCOMMIT], [ ])
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	force_lazy_lock="1"
 	;;
   *-*-dragonfly*)
 	abi="elf"
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	;;
   *-*-openbsd*)
 	abi="elf"
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	force_tls="0"
 	;;
   *-*-bitrig*)
 	abi="elf"
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	;;
   *-*-linux-android)
 	dnl syscall(2) and secure_getenv(3) are exposed by _GNU_SOURCE.
@@ -389,7 +384,6 @@ case "${host}" in
 	abi="elf"
 	AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
 	AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED], [ ])
 	AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
 	AC_DEFINE([JEMALLOC_C11ATOMICS])
 	force_tls="0"
@@ -401,7 +395,6 @@ case "${host}" in
 	abi="elf"
 	AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
 	AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED], [ ])
 	AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
 	AC_DEFINE([JEMALLOC_USE_CXX_THROW], [ ])
 	default_munmap="0"
@@ -418,11 +411,9 @@ case "${host}" in
                           [abi="elf"],
                           [abi="aout"])
 	AC_MSG_RESULT([$abi])
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	;;
   *-*-solaris2*)
 	abi="elf"
-	AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
 	RPATH='-Wl,-R,$(1)'
 	dnl Solaris needs this for sigwait().
 	CPPFLAGS="$CPPFLAGS -D_POSIX_PTHREAD_SEMANTICS"
@@ -1580,12 +1571,33 @@ dnl Check for madvise(2).
 JE_COMPILABLE([madvise(2)], [
 #include <sys/mman.h>
 ], [
-	{
-		madvise((void *)0, 0, 0);
-	}
+	madvise((void *)0, 0, 0);
 ], [je_cv_madvise])
 if test "x${je_cv_madvise}" = "xyes" ; then
-  AC_DEFINE([JEMALLOC_HAVE_MADVISE], [ ])
+  dnl Check for madvise(..., MADV_FREE).
+  JE_COMPILABLE([madvise(..., MADV_FREE)], [
+#include <sys/mman.h>
+], [
+	madvise((void *)0, 0, MADV_FREE);
+], [je_cv_madv_free])
+  if test "x${je_cv_madv_free}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
+  fi
+
+  dnl Check for madvise(..., MADV_DONTNEED).
+  JE_COMPILABLE([madvise(..., MADV_DONTNEED)], [
+#include <sys/mman.h>
+], [
+	madvise((void *)0, 0, MADV_DONTNEED);
+], [je_cv_madv_dontneed])
+  if test "x${je_cv_madv_dontneed}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED], [ ])
+  fi
+
+  if test "x${je_cv_madv_free}" = "xyes" \
+       -o "x${je_cv_madv_dontneed}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_HAVE_MADVISE], [ ])
+  fi
 fi
 
 dnl ============================================================================
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 4d2daea..baf12d4 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -56,11 +56,6 @@
 #undef JEMALLOC_HAVE_BUILTIN_CLZ
 
 /*
- * Defined if madvise(2) is available.
- */
-#undef JEMALLOC_HAVE_MADVISE
-
-/*
  * Defined if os_unfair_lock_*() functions are available, as provided by Darwin.
  */
 #undef JEMALLOC_OS_UNFAIR_LOCK
@@ -249,18 +244,20 @@
 #undef JEMALLOC_SYSCTL_VM_OVERCOMMIT
 #undef JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY
 
+/* Defined if madvise(2) is available. */
+#undef JEMALLOC_HAVE_MADVISE
+
 /*
  * Methods for purging unused pages differ between operating systems.
  *
- *   madvise(..., MADV_DONTNEED) : On Linux, this immediately discards pages,
- *                                 such that new pages will be demand-zeroed if
- *                                 the address region is later touched.
- *   madvise(..., MADV_FREE) : On FreeBSD and Darwin, this marks pages as being
- *                             unused, such that they will be discarded rather
- *                             than swapped out.
+ *   madvise(..., MADV_FREE) : This marks pages as being unused, such that they
+ *                             will be discarded rather than swapped out.
+ *   madvise(..., MADV_DONTNEED) : This immediately discards pages, such that
+ *                                 new pages will be demand-zeroed if the
+ *                                 address region is later touched.
  */
-#undef JEMALLOC_PURGE_MADVISE_DONTNEED
 #undef JEMALLOC_PURGE_MADVISE_FREE
+#undef JEMALLOC_PURGE_MADVISE_DONTNEED
 
 /* Define if operating system has alloca.h header. */
 #undef JEMALLOC_HAS_ALLOCA_H
diff --git a/src/pages.c b/src/pages.c
index 647952a..395ace9 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -171,14 +171,14 @@ pages_purge(void *addr, size_t size)
 	VirtualAlloc(addr, size, MEM_RESET, PAGE_READWRITE);
 	unzeroed = true;
 #elif defined(JEMALLOC_HAVE_MADVISE)
-#  ifdef JEMALLOC_PURGE_MADVISE_DONTNEED
-#    define JEMALLOC_MADV_PURGE MADV_DONTNEED
-#    define JEMALLOC_MADV_ZEROS true
-#  elif defined(JEMALLOC_PURGE_MADVISE_FREE)
+#  if defined(JEMALLOC_PURGE_MADVISE_FREE)
 #    define JEMALLOC_MADV_PURGE MADV_FREE
 #    define JEMALLOC_MADV_ZEROS false
+#  elif defined(JEMALLOC_PURGE_MADVISE_DONTNEED)
+#    define JEMALLOC_MADV_PURGE MADV_DONTNEED
+#    define JEMALLOC_MADV_ZEROS true
 #  else
-#    error "No madvise(2) flag defined for purging unused dirty pages."
+#    error No madvise(2) flag defined for purging unused dirty pages
 #  endif
 	int err = madvise(addr, size, JEMALLOC_MADV_PURGE);
 	unzeroed = (!JEMALLOC_MADV_ZEROS || err != 0);