From: Byungki Lee <dominicus79@xxxxxxxxx>
If there's not enough free sections each of which consistis of large segments,
we can hit no free section for upcoming section allocation. Let's reclaim some
prefree segments by writing checkpoints.
Signed-off-by: Byungki Lee <dominicus79@xxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>