This is the output from btrfs check --repair /dev/xvdc2

enabling repair mode
Checking filesystem on /dev/xvdc2
UUID: c88dbf5b-3513-4966-b3d6-5bb6c9b7717e
checking extents
Fixed 0 roots.
checking free space cache
cache and super generation don't match, space cache will be invalidated
checking fs roots
checking csums
checking root refs
found 9380937728 bytes used err is 0
total csum bytes: 8061100
total tree bytes: 230670336
total fs tree bytes: 181600256
total extent tree bytes: 34013184
btree space waste bytes: 41120097
file data blocks allocated: 10417725440
referenced 8217731072


Then I get this:

Filesystem 1MB-blocks Used Available Use% Mounted on
/dev/xvda2 11249MB 9918MB 0MB 100% /