[core] periodically malloc_trim() to release mem (fixes #3084)

x-ref:
  "Memory fragmentation with HTTP/2 enabled"
  https://redmine.lighttpd.net/issues/3084

SConstruct

@@ -429,6 +429,7 @@ if 1:
 		'localtime_r',
 		'lstat',
 		'madvise',
+		'malloc_trim',
 		'mallopt',
 		'memcpy',
 		'mempcpy',

configure.ac

@@ -1500,6 +1500,7 @@ AC_CHECK_FUNCS([\
   localtime_r \
   lstat \
   madvise \
+  malloc_trim \
   mallopt \
   memcpy \
   mempcpy \

src/CMakeLists.txt

@@ -173,6 +173,7 @@ check_function_exists(kqueue HAVE_KQUEUE)
 check_function_exists(localtime_r HAVE_LOCALTIME_R)
 check_function_exists(lstat HAVE_LSTAT)
 check_function_exists(madvise HAVE_MADVISE)
+check_function_exists(malloc_trim HAVE_MALLOC_TRIM)
 check_function_exists(mallopt HAVE_MALLOPT)
 check_function_exists(memcpy HAVE_MEMCPY)
 check_function_exists(mempcpy HAVE_MEMPCPY)

src/config.h.cmake

@@ -127,6 +127,7 @@
 #cmakedefine  HAVE_LOCALTIME_R
 #cmakedefine  HAVE_LSTAT
 #cmakedefine  HAVE_MADVISE
+#cmakedefine  HAVE_MALLOC_TRIM
 #cmakedefine  HAVE_MALLOPT
 #cmakedefine  HAVE_MEMCPY
 #cmakedefine  HAVE_MEMPCPY

src/meson.build

@@ -125,6 +125,7 @@ conf_data.set('HAVE_KQUEUE', compiler.has_function('kqueue', args: defs))
 conf_data.set('HAVE_LOCALTIME_R', compiler.has_function('localtime_r', args: defs))
 conf_data.set('HAVE_LSTAT', compiler.has_function('lstat', args: defs))
 conf_data.set('HAVE_MADVISE', compiler.has_function('madvise', args: defs))
+conf_data.set('HAVE_MALLOC_TRIM', compiler.has_function('malloc_trim', args: defs))
 conf_data.set('HAVE_MALLOPT', compiler.has_function('mallopt', args: defs))
 conf_data.set('HAVE_MEMCPY', compiler.has_function('memcpy', args: defs))
 conf_data.set('HAVE_MEMPCPY', compiler.has_function('mempcpy', args: defs))

src/server.c

@@ -72,6 +72,10 @@ static const buffer default_server_tag = { CONST_STR_LEN(PACKAGE_DESC)+1, 0 };
 #endif
 #endif
 #include <malloc.h>
+#if defined(HAVE_MALLOC_TRIM)
+static int(*malloc_trim_fn)(size_t);
+static size_t malloc_top_pad;
+#endif
 #endif
 
 #include "sys-crypto.h"
@@ -1872,6 +1876,9 @@ static void server_handle_sigalrm (server * const srv, unix_time64_t mono_ts, un
 					/* clear request and connection pools every 64 secs */
 					request_pool_free();
 					connections_pool_clear(srv);
+				  #if defined(HAVE_MALLOC_TRIM)
+					if (malloc_trim_fn) malloc_trim_fn(malloc_top_pad);
+				  #endif
 					/* attempt to restart dead piped loggers every 64 secs */
 					if (0 == srv->srvconf.max_worker)
 						fdevent_restart_logger_pipes(mono_ts);
@@ -1997,6 +2004,23 @@ int main (int argc, char **argv) {
         if (mallopt_fn) mallopt_fn(M_ARENA_MAX, 2); /*(ignore error, if any)*/
     }
   #endif
+  #endif
+
+  #if defined(HAVE_MALLOC_TRIM)
+    malloc_top_pad = 524288;
+    {
+        const char * const top_pad_str = getenv("MALLOC_TOP_PAD_");
+        if (top_pad_str) {
+            unsigned long top_pad = strtoul(top_pad_str, NULL, 10);
+            if (top_pad != ULONG_MAX) malloc_top_pad = (size_t)top_pad;
+        }
+    }
+  #ifdef LIGHTTPD_STATIC
+    malloc_trim_fn = malloc_trim;
+  #else
+    malloc_trim_fn =
+      (int (*)(size_t))(intptr_t)dlsym(RTLD_DEFAULT,"malloc_trim");
+  #endif
   #endif
 
     /* for nice %b handling in strftime() */