MDEV-5746: Slow file extend when innodb_use_fallocate=1 and SSD

file storage.

Analysis: posix_fallocate was called using 0 as offset and len as
desired size. This is not optimal for SSDs.

Fix: Call posix_fallocate with correct offset i.e. current file size
and extend the file from there len bytes.

storage/innobase/fil/fil0fil.c

@@ -4110,12 +4110,22 @@ fil_extend_space_to_desired_size(
 
 #ifdef HAVE_POSIX_FALLOCATE
 	if (srv_use_posix_fallocate) {
-		offset_high = size_after_extend * page_size / (4ULL*1024*1024*1024);
-		offset_low = size_after_extend * page_size % (4ULL*1024*1024*1024);
+		ib_int64_t start_offset = start_page_no * page_size;
+		ib_int64_t end_offset   = (size_after_extend - start_page_no) * page_size;
+		ib_int64_t desired_size = size_after_extend*page_size;
 
 		mutex_exit(&fil_system->mutex);
-		success = os_file_set_size(node->name, node->handle,
-				offset_low, offset_high);
+
+		if (posix_fallocate(node->handle, start_offset, end_offset) == -1) {
+			fprintf(stderr, "InnoDB: Error: preallocating file "
+				"space for file \'%s\' failed. Current size "
+				" %lld, len %lld, desired size %lld\n",
+				node->name, start_offset, end_offset, desired_size);
+			success = FALSE;
+		} else {
+			success = TRUE;
+		}
+
 		mutex_enter(&fil_system->mutex);
 
 		if (success) {

storage/xtradb/fil/fil0fil.c

@@ -4953,12 +4953,22 @@ fil_extend_space_to_desired_size(
 
 #ifdef HAVE_POSIX_FALLOCATE
 	if (srv_use_posix_fallocate) {
-		offset_high = size_after_extend * page_size / (4ULL*1024*1024*1024);
-		offset_low = size_after_extend * page_size % (4ULL*1024*1024*1024);
+		ib_int64_t start_offset = start_page_no * page_size;
+		ib_int64_t end_offset   = (size_after_extend - start_page_no) * page_size;
+		ib_int64_t desired_size = size_after_extend*page_size;
 
 		mutex_exit(&fil_system->mutex);
-		success = os_file_set_size(node->name, node->handle,
-					   offset_low, offset_high);
+
+		if (posix_fallocate(node->handle, start_offset, end_offset) == -1) {
+			fprintf(stderr, "InnoDB: Error: preallocating file "
+				"space for file \'%s\' failed. Current size "
+				" %lld, len %lld, desired size %lld\n",
+				node->name, start_offset, end_offset, desired_size);
+			success = FALSE;
+		} else {
+			success = TRUE;
+		}
+
 		mutex_enter(&fil_system->mutex);
 
 		if (success) {