I always read (from sources like LKML, not random blog posts) that defrag on SSD is simply useless because you never know the actual physical placement of your

I always read (from sources like LKML, not random blog posts) that defrag on SSD is simply useless because you never know the actual physical placement of your blocks. You can write a sequential 512 MB chunk of data in a single file and have it exploded in 500k+ 4k blocks in different locations (or vice versa — a bunch of random writes to different sectors can be compacted into a single linear block). If you really need to defrag SSD (which somewhat helps IME if it was heavily used up to 100% capacity), copy everything to other storage, wipe it (preferably with NVMe/SATA commands, or at least do a full TRIM), and then copy everything back.