ext4: don't use CR_BEST_AVAIL_LEN for non-regular files

Using CR_BEST_AVAIL_LEN only make sense for regular files, as for
non-regular files we never normalize the allocation request length i.e.
goal len is same as original length (ac_g_ex.fe_len == ac_o_ex.fe_len).

Hence there is no scope of trimming the goal length to make it
satisfy original request len. Thus this patch avoids using
CR_BEST_AVAIL_LEN criteria for non-regular files request.

Cc: [email protected]
Fixes: 33122aa ("ext4: Add allocation criteria 1.5 (CR1_5)")
Reported-by: Eric Whitney <[email protected]>
Signed-off-by: Ritesh Harjani (IBM) <[email protected]>
Tested-by: Eric Whitney <[email protected]>
Link: https://lore.kernel.org/r/2a694c748ff8b8c4b416995a24f06f07b55047a8.1689516047.git.ritesh.list@gmail.com
Signed-off-by: Theodore Ts'o <[email protected]>

Author: riteshharjani

fs/ext4/mballoc.c

@@ -966,7 +966,18 @@ static void ext4_mb_choose_next_group_goal_fast(struct ext4_allocation_context *
 		}
 	}
 
-	*new_cr = CR_BEST_AVAIL_LEN;
+	/*
+	 * CR_BEST_AVAIL_LEN works based on the concept that we have
+	 * a larger normalized goal len request which can be trimmed to
+	 * a smaller goal len such that it can still satisfy original
+	 * request len. However, allocation request for non-regular
+	 * files never gets normalized.
+	 * See function ext4_mb_normalize_request() (EXT4_MB_HINT_DATA).
+	 */
+	if (ac->ac_flags & EXT4_MB_HINT_DATA)
+		*new_cr = CR_BEST_AVAIL_LEN;
+	else
+		*new_cr = CR_GOAL_LEN_SLOW;
 }
 
 /*