If userspace issue a fstrim with a range not involve prefree segments,
it will reuse these segments without discard. This patch fix it.
Signed-off-by: NYunlei He <heyunlei@huawei.com>
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>