This is experimental clone() (vs. fork()) patch for mpm-itk apache 2.2.
Really I see no perfomance benefits, but only little RAM. But using
CLONE_VFORK must relax scheduling in theory.

Primary - for experiments with LXC.

(c) Denis Kaganovich, <mahatma@eu.by>
Licensed under the same terms as the rest of Apache (or Anarchy license).

First I remove vfork by default die to segfaults. But then I back to vfork
on my servers, keepend defaults. So, to use vfork add "CloneFlags 16384" in
mpm_itk config section.

--- a/server/mpm/experimental/itk/itk.c	2014-02-28 11:04:38.000000000 +0300
+++ b/server/mpm/experimental/itk/itk.c	2014-02-28 11:37:45.292890651 +0300
@@ -104,6 +104,19 @@
 #define HARD_THREAD_LIMIT 1
 #endif
 
+#ifdef __linux__
+#include <syscall.h>
+#include <linux/version.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,5,49) && defined(CLONE_FS)
+#define ITK_USE_CLONE 1
+static int clone_flags1 = 0, clone_flags2 = 0;
+#else
+#define ITK_USE_CLONE 0
+#endif
+#else
+#define ITK_USE_CLONE 0
+#endif
+
 /* config globals */
 
 int ap_threads_per_child=0;         /* Worker threads per child */
@@ -713,7 +726,11 @@ static void child_main(int child_num_arg
          */
 
         {
+#if ITK_USE_CLONE
+            pid_t pid = syscall(SYS_clone, clone_flags1, 0, NULL, NULL), child_pid;
+#else
             pid_t pid = fork(), child_pid;
+#endif
             int status;
             switch (pid) {
             case -1:
@@ -728,6 +745,12 @@ static void child_main(int child_num_arg
                 }
                 exit(0);
             default: /* parent; just wait for child to be done */
+#if ITK_USE_CLONE
+                if (clone_flags1 & CLONE_VFORK) {
+                    /* pid always done, ignore interrupts (die means die) */
+                    child_pid = waitpid(pid, &status, WNOHANG);
+                } else
+#endif
                 do {
                     child_pid = waitpid(pid, &status, 0);
                 } while (child_pid == -1 && errno == EINTR);
@@ -804,6 +827,8 @@ static int make_child(server_rec *s, int
     if ((pid = os_fork(unixd_config.user_name)) == -1) {
 #elif defined(TPF)
     if ((pid = os_fork(s, slot)) == -1) {
+#elif ITK_USE_CLONE
+    if ((pid = syscall(SYS_clone, clone_flags2, 0, NULL, NULL)) == -1) {
 #else
     if ((pid = fork()) == -1) {
 #endif
@@ -1426,6 +1451,10 @@ static int itk_pre_config(apr_pool_t *p,
 #ifdef AP_MPM_WANT_SET_MAX_MEM_FREE
     ap_max_mem_free = APR_ALLOCATOR_MAX_FREE_UNLIMITED;
 #endif
+#if ITK_USE_CLONE
+    clone_flags1 = SIGCHLD;
+    clone_flags2 = SIGCHLD | CLONE_FS;
+#endif
 
     apr_cpystrn(ap_coredump_dir, ap_server_root, sizeof(ap_coredump_dir));
 
@@ -1678,6 +1707,19 @@ static const char *set_nice_value (cmd_p
     return NULL;
 }
 
+#if ITK_USE_CLONE
+static const char *set_clone_flags(cmd_parms *cmd, void *dummy, const char *flags1,  const char *flags2)
+{
+    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
+    if (err != NULL)
+        return err;
+
+    clone_flags1 = (SIGCHLD) ^ atoi(flags1);
+    clone_flags2 = (SIGCHLD | CLONE_FS) ^ (flags2 ? atoi(flags2) : 0);
+    return NULL;
+}
+#endif
+
 static const command_rec itk_cmds[] = {
 UNIX_DAEMON_COMMANDS,
 LISTEN_COMMANDS,
@@ -1697,6 +1739,10 @@ AP_INIT_TAKE1("MaxClientsVHost", set_max
               "Maximum number of children alive at the same time for this virtual host."),
 AP_INIT_TAKE1("NiceValue", set_nice_value, NULL, RSRC_CONF|ACCESS_CONF,
               "Set nice value for the given vhost, from -20 (highest priority) to 19 (lowest priority)."),
+#if ITK_USE_CLONE
+AP_INIT_TAKE12("CloneFlags", set_clone_flags, NULL, RSRC_CONF,
+              "XOR to default (SIGCHLD, SIGCHLD|CLONE_FS) clone flags. See /usr/include/{linux,bits}/sched.h or 'man 2 clone'"),
+#endif
 AP_GRACEFUL_SHUTDOWN_TIMEOUT_COMMAND,
 { NULL }
 };