ext4: Fix hueristic which avoids group preallocation for closed files

The hueristic was designed to avoid using locality group preallocation
when writing the last segment of a closed file.  Fix it by move
setting size to the maximum of size and isize until after we check
whether size == isize.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4189,7 +4189,6 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
 	size = ac->ac_o_ex.fe_logical + ac->ac_o_ex.fe_len;
 	isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
 		>> bsbits;
-	size = max(size, isize);
 
 	if ((size == isize) &&
 	    !ext4_fs_is_busy(sbi) &&
@@ -4199,6 +4198,7 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
 	}
 
 	/* don't use group allocation for large files */
+	size = max(size, isize);
 	if (size >= sbi->s_mb_stream_request) {
 		ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
 		return;