posixfs: use fadvise "dontneed"? #150
Description
If a store user reads or writes a lot of data, caching might not be beneficial.
E.g. if a backup tool like borgbackup does a backup and writes huge amounts packs/<content-hash-of-pack>, it is rather unlikely that it will read the packs again soon afterwards.
Similar for a restore: if it reads packs, it will often not need to read the same data from the packs again (some exceptions like the all-zero chunk will likely be cached in the backup program).