diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 3e02dce..2a923d3 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -451,8 +451,27 @@ pg_flush_data(int fd, off_t offset, off_t nbytes)
 		 * We map the file (mmap()), tell the kernel to sync back the contents
 		 * (msync()), and then remove the mapping again (munmap()).
 		 */
+
+		/* mmap() need exact length when we want to map whole file */
+		if ((offset == 0) && (nbytes == 0))
+		{
+			int pagesize = sysconf(_SC_PAGESIZE);
+
+			nbytes = lseek(fd, 0, SEEK_END);
+			if (nbytes < 0)
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not determine dirty data size: %m")));
+
+			/* aling to pagesize with underestimation */
+			nbytes = (nbytes/pagesize)*pagesize;
+
+			if (nbytes == 0)
+				return;
+		}
+
 		p = mmap(NULL, nbytes,
-				 PROT_READ | PROT_WRITE, MAP_SHARED,
+				 PROT_READ, MAP_SHARED,
 				 fd, offset);
 		if (p == MAP_FAILED)
 		{
@@ -2920,7 +2939,8 @@ pre_sync_fname(const char *fname, bool isdir, int elevel)
 	 * pg_flush_data() ignores errors, which is ok because this is only a
 	 * hint.
 	 */
-	pg_flush_data(fd, 0, 0);
+	if (!isdir)
+		pg_flush_data(fd, 0, 0);
 
 	(void) CloseTransientFile(fd);
 }