Use mlock2() instead of mlock() on Linux and use mlockall(MCL_FUTURE).

Use mlock2() instead of mlock() on Linux:
  - mlock2() allows a third argument MLOCK_ONFAULT, which allow to
    lock the pages in a range before touching them, so mlock2()
    can be called before touching all pages instead of after.
  - "vmtouch -t -l" some_file would not keep the pages in cache
    after touching them, so at the lock() step they needed to
    be read again from disk. After this patch files are cached
    twice as fast on this system.

Use mlockall(MCL_FUTURE) instead of mlockall(MCL_CURRENT):
  - Set mlockall(MCL_FUTURE) before touching pages to have similar
    behaviour as the mlock2() approach above.

vmtouch.c

@@ -169,7 +169,11 @@ void usage() {
   printf("Usage: vmtouch [OPTIONS] ... FILES OR DIRECTORIES ...\n\nOptions:\n");
   printf("  -t touch pages into memory\n");
   printf("  -e evict pages from memory\n");
+#if defined(__linux__)
+  printf("  -l lock pages in physical memory with mlock2(2)\n");
+#else
   printf("  -l lock pages in physical memory with mlock(2)\n");
+#endif
   printf("  -L lock pages in physical memory with mlockall(2)\n");
   printf("  -d daemon mode\n");
   printf("  -m <size> max file size to touch\n");
@@ -614,6 +618,13 @@ void vmtouch_file(char *path) {
     char *mincore_array = malloc(pages_in_range);
     if (mincore_array == NULL) fatal("Failed to allocate memory for mincore array (%s)", strerror(errno));
 
+#if defined(__linux__)
+    if (o_lock) {
+      if (mlock2(mem, len_of_range, MLOCK_ONFAULT))
+        fatal("mlock2: %s (%s)", path, strerror(errno));
+    }
+#endif
+
     // 3rd arg to mincore is char* on BSD and unsigned char* on linux
     if (mincore(mem, len_of_range, (void*)mincore_array)) fatal("mincore %s (%s)", path, strerror(errno));
     for (i=0; i<pages_in_range; i++) {
@@ -657,10 +668,12 @@ void vmtouch_file(char *path) {
     free(mincore_array);
   }
 
+#ifndef __linux__
   if (o_lock) {
     if (mlock(mem, len_of_range))
       fatal("mlock: %s (%s)", path, strerror(errno));
   }
+#endif
 
   bail:
 
@@ -1028,6 +1041,18 @@ int main(int argc, char **argv) {
 
   gettimeofday(&start_time, NULL);
 
+  if (o_lock || o_lockall) {
+    if (o_lockall) {
+      if (mlockall(MCL_FUTURE))
+        fatal("unable to mlockall (%s)", strerror(errno));
+    }
+
+    if (o_pidfile) {
+      register_signals_for_pidfile();
+      write_pidfile();
+    }
+  }
+
   if (o_batch) {
       vmtouch_batch_crawl(o_batch);
   }
@@ -1042,16 +1067,6 @@ int main(int argc, char **argv) {
   double  elapsed                  = (end_time.tv_sec - start_time.tv_sec) + (double)(end_time.tv_usec - start_time.tv_usec)/1000000.0;
 
   if (o_lock || o_lockall) {
-    if (o_lockall) {
-      if (mlockall(MCL_CURRENT))
-        fatal("unable to mlockall (%s)", strerror(errno));
-    }
-
-    if (o_pidfile) {
-      register_signals_for_pidfile();
-      write_pidfile();
-    }
-
     if (!o_quiet) printf("LOCKED %" PRId64 " pages (%s)\n", total_pages, pretty_print_size(total_pages_size));
 
     if (o_wait) reopen_all();