linux - missing disk space on ext4

I have a case like this.
One partition 7.7GB, And I cannot where this space was used.

/# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            488M     0  488M   0% /dev
tmpfs           100M   11M   89M  11% /run
/dev/xvda1      7.7G  7.7G   32M 100% /
tmpfs           496M     0  496M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           496M     0  496M   0% /sys/fs/cgroup
tmpfs           100M     0  100M   0% /run/user/1000

Then i check all dirs strtging from /

/# ls -c1 |xargs du -sh
120K    tmp
644M    boot
0   initrd.img
0   initrd.img.old
0   vmlinuz
0   vmlinuz.old
0   sys
11M run
5.8M    etc
16M bin
14M sbin
8.0K    snap
36K root
1.3G    lib
4.0K    lib64
268M    home
0   dev
0   proc
884M    var
4.6G    usr
4.0K    srv
4.0K    media
4.0K    mnt
4.0K    opt
16K lost+found

And root directory doesn't contain any big files

/# ls -Shsr
total 96K
   0 sys      0 vmlinuz.old     0 initrd.img.old     0 run  4.0K var  4.0K tmp  4.0K snap  4.0K opt  4.0K media  4.0K lib   4.0K etc   12K sbin   16K lost+found
   0 proc     0 vmlinuz         0 initrd.img         0 dev  4.0K usr  4.0K srv  4.0K root  4.0K mnt  4.0K lib64  4.0K home  4.0K bin   12K boot

Where could be this space use ?

This is ext4 filesystem
/dev/xvda1 / ext4 rw,relatime,discard,data=ordered 0 0