fallocate.patch

diff --git a/configure b/configure
index 45c8eef..2772e2f 100755
--- a/configure
+++ b/configure
@@ -12473,7 +12473,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
+for ac_func in cbrt dlopen fallocate fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/configure.in b/configure.in
index c878b4e..685b6c5 100644
--- a/configure.in
+++ b/configure.in
@@ -1446,7 +1446,7 @@ PGAC_FUNC_WCSTOMBS_L
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
+AC_CHECK_FUNCS([cbrt dlopen fallocate fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 173b982..d27adf3 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -225,6 +225,46 @@ dsm_impl_can_resize(void)
 
 #ifdef USE_DSM_POSIX
 /*
+ * Set the size of a virtual memory region associate with a file descriptor.
+ * On Linux, also ensure that virtual memory is actually allocated by the
+ * operating system to avoid nasty surprises later.
+ *
+ * Returns non-zero if either truncation or allocation fails, and sets errno.
+ */
+static int
+dsm_impl_posix_resize(int fd, off_t size)
+{
+		int rc;
+
+		/* Truncate (or extend) the file to the requested size. */
+		rc = ftruncate(fd, size);
+
+#ifdef HAVE_FALLOCATE
+#ifdef __linux__
+		/*
+		 * On Linux, a shm_open fd is backed by a tmpfs file.  After resizing
+		 * with ftruncate it may contain a hole.  Accessing memory backed by a
+		 * hole causes tmpfs to allocate pages, which fails with SIGBUS if
+		 * there is no virtual memory available.  So we ask tmpfs to allocate
+		 * pages here, so we can fail gracefully with ENOSPC now rather than
+		 * risking SIGBUS later.
+		 */
+		if (rc == 0)
+		{
+			rc = fallocate(fd, 0, 0, size);
+			if (rc != 0 && errno == ENOSYS)
+			{
+				/* Kernel too old (< 2.6.23). */
+				rc = 0;
+			}
+		}
+#endif
+#endif
+
+		return rc;
+}
+
+/*
  * Operating system primitives to support POSIX shared memory.
  *
  * POSIX shared memory segments are created and attached using shm_open()
@@ -319,7 +359,8 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 		}
 		request_size = st.st_size;
 	}
-	else if (*mapped_size != request_size && ftruncate(fd, request_size))
+	else if (*mapped_size != request_size &&
+			 dsm_impl_posix_resize(fd, request_size) != 0)
 	{
 		int			save_errno;
 
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index b621ff2..2ed2b0d 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -149,6 +149,9 @@
 /* Define to 1 if you have the <editline/readline.h> header file. */
 #undef HAVE_EDITLINE_READLINE_H
 
+/* Define to 1 if you have the `fallocate' function. */
+#undef HAVE_FALLOCATE
+
 /* Define to 1 if you have the `fdatasync' function. */
 #undef HAVE_FDATASYNC