f2fs: do not issue small discard commands during checkpoint

If there're huge # of small discards, this will increase checkpoint latency
insanely. Let's issue small discards only by trim.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -2193,7 +2193,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
 			len = next_pos - cur_pos;
 
 			if (f2fs_sb_has_blkzoned(sbi) ||
-			    (force && len < cpc->trim_minlen))
+					!force || len < cpc->trim_minlen)
 				goto skip;
 
 			f2fs_issue_discard(sbi, entry->start_blkaddr + cur_pos,