During defragment, we missed to trigger fragmented blocks migration
for below condition:
In defragment region:
- total number of valid blocks is smaller than 512;
- the tail part of the region are all holes;
In addtion, return zero to user via range->len if there is no
fragmented blocks.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>