In general, don't worry about it. Unlike MacOS HFS, the ext2fs is designed
to automatically reduce fragmentation. Read about its design in the
Linux System Administrator's Guide, at:

  http://linuxwww.db.erau.edu/SAG/ 

If you're just dying to defragment, you can compile the linux filesystem
defragmenter. But it may need to be ported to overcome endian issues.
(MkLinux still uses a big-endian version of e2fs, linux-pmac offers
both, intel uses little-endian, and of course intel and PPC have opposite
CPU endianness.) If you do port and test it, be sure to upload it to
MkArchive! (And update this FAQ.)

  ftp://sunsite.unc.edu/pub/Linux/system/Filesystems/defrag-0.6.tar.gz 

Allen Briggs points out that you can also simply backup your filesystem,
mkfs it (write a new filesystem to the partition), and restore the
old data.

jonh@cs.dartmouth.edu