jun@jun-VirtualBox:~/workdir/b6ce39eeb6de8887e66a$ filefrag -b -v /mnt/large-disk/faketmpfs/disk.img 
filefrag: -b needs a blocksize option, assuming 1024-byte blocks.
Filesystem type is: ef53
File size of /mnt/large-disk/faketmpfs/disk.img is 268435456 (262144 blocks of 1024 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:
   0:        0..     131:   14942208..  14942339:    132:            
   1:      136..    2047:   14942344..  14944255:   1912:   14942340:
   2:     4100..    4103:   14946308..  14946311:      4:   14944256:
   3:     4108..    4115:   14944256..  14944263:      8:   14946312:
   4:     4124..    4127:   14944272..  14944275:      4:   14944264:
   5:     4132..    4135:   14946340..  14946343:      4:   14944276:
   6:     4152..    4155:   14944296..  14944299:      4:   14946344:
   7:     4180..    4187:   14944324..  14944331:      8:   14944300:
   8:     9020..    9023:   15606588..  15606591:      4:   14944332:
   9:    45056..   65535:   15568896..  15589375:  20480:   15606592:
  10:    65536..   65539:   14950400..  14950403:      4:   15589376:
  11:   118784..  122879:   14970880..  14974975:   4096:   14950404:
  12:   260096..  262143:   14964736..  14966783:   2048:   14974976: eof
/mnt/large-disk/faketmpfs/disk.img: 13 extents found
jun@jun-VirtualBox:~/workdir/b6ce39eeb6de8887e66a$ ls -lsh /mnt/large-disk/faketmpfs/disk.img 
29M -rw-r--r-- 1 root root 256M Aug 26 10:53 /mnt/large-disk/faketmpfs/disk.img