f2fs: correct search area in get_new_segment

get_new_segment starts from current segment position, tries to search a
free segment among its right neighbors locate in same section.

But previously our search area was set as [current segment, max segment],
which means we have to search to more bits in free_segmap bitmap for some
worse cases. So here we correct the search area to [current segment, last
segment in section] to avoid unnecessary searching.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -874,9 +874,8 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 
 	if (!new_sec && ((*newseg + 1) % sbi->segs_per_sec)) {
 		segno = find_next_zero_bit(free_i->free_segmap,
-					MAIN_SEGS(sbi), *newseg + 1);
-		if (segno - *newseg < sbi->segs_per_sec -
-					(*newseg % sbi->segs_per_sec))
+				(hint + 1) * sbi->segs_per_sec, *newseg + 1);
+		if (segno < (hint + 1) * sbi->segs_per_sec)
 			goto got_it;
 	}
 find_other_zone: