or you can just have memory fragmentation

compaction doesn't require a lot of memory but it's slow and intrusive; it has to know where all your buffer pointers are

Obviously permanently wasting memory on fragmentation is not an option on a device that typically has 24kb memory. Especially not just so you can specify long filenames for the shell, when the filesystem doesn’t even support those filenames.

the alternative they chose was to permanently waste memory on fixed-size struct fields, so i guess it was actually an option

malloc on the pdp-11 never compacted of course

the filesystem supported 14 characters for the basename, but evidently we're talking about code with a 14-character limit on the pathname, not the basename

You don’t need compaction to reuse fixed size structures. I presume their priorities were with creating a working system, not one that answers to the ‘requirements’ of 50 years into the future.

you don't need compaction to reuse heap-allocated memory either

wasted memory due to heap fragmentation is very similar to wasted memory due to slack space in fixed-size structure fields