Return free memory more aggressively.

Have free(3) call sbrk(2) when there's 4 MB to free (default on Linux
seems to be 128).

Patch by Fabian Mauchle.

configure.ac

@@ -1,12 +1,14 @@
 dnl Copyright (c) 2006-2010, UNINETT AS
-dnl Copyright (c) 2010-2012, NORDUnet A/S
+dnl Copyright (c) 2010-2013, NORDUnet A/S
 dnl See LICENSE for licensing information.
 
 AC_INIT(radsecproxy, 1.7-dev, radsecproxy@uninett.no)
 AC_CANONICAL_TARGET
 AM_INIT_AUTOMAKE
 AC_PROG_CC
 AC_PROG_RANLIB
+AC_CHECK_FUNCS([mallopt])
+
 udp=yes
 AC_ARG_ENABLE(udp,
   [  --enable-udp whether to enable UDP transport: yes/no; default yes ],

radsecproxy.c

@@ -39,6 +39,9 @@
 #include <string.h>
 #include <unistd.h>
 #include <limits.h>
+#if defined(HAVE_MALLOPT)
+#include <malloc.h>
+#endif
 #ifdef SYS_SOLARIS9
 #include <fcntl.h>
 #endif
@@ -3335,6 +3338,10 @@ int radsecproxy_main(int argc, char **argv) {
 	debugx(1, DBG_ERR, "pthread_attr_init failed");
     if (pthread_attr_setstacksize(&pthread_attr, PTHREAD_STACK_SIZE))
 	debugx(1, DBG_ERR, "pthread_attr_setstacksize failed");
+#if defined(HAVE_MALLOPT)
+    if (mallopt(M_TRIM_THRESHOLD, 4 * 1024) != 1)
+	debugx(1, DBG_ERR, "mallopt failed");
+#endif
 
     for (i = 0; i < RAD_PROTOCOUNT; i++)
 	protodefs[i] = protoinits[i](i);