$ mkdir test;ls -ld test;for((C=0;C<10000;C++))do>test/$C;done;rm -f test/*;ls -ld test
drwxr-xr-x 2 compis users 4096 2023-11-19 13:05 test
drwxr-xr-x 2 compis users 262144 2023-11-19 13:05 test

       -D     Optimize  directories in file system.  This option causes e2fsck
              to try to optimize all directories, either by  re-indexing  them
              if  the  file system supports directory indexing,  or by sorting
              and compressing directories for smaller directories, or for file
              systems using traditional linear directories.

              Even  without the -D option, e2fsck may sometimes optimize a few
              directories --- for example, if directory  indexing  is  enabled
              and  a directory is not indexed and would benefit from being in-
              dexed, or if the index structures are corrupted and need  to  be
              rebuilt.   The -D option forces all directories in the file sys-
              tem to be optimized.  This can  sometimes  make  them  a  little
              smaller  and  slightly  faster  to  search, but in practice, you
              should rarely need to use this option.

              The -D option will detect directory entries with duplicate names
              in  a  single  directory, which e2fsck normally does not enforce
              for performance reasons.