O pacote readahead está disponível apenas para o debian Wheezy e Jessie. Também foi removido do systemd.
systemd's readahead implementation has been removed. In many circumstances it didn't give expected benefits even for rotational disk drives and was becoming less relevant in the age of SSDs. As none of the developers has been using rotating media anymore, and nobody stepped up to actively maintain this component of systemd it has now been removed.
Freedesktop-systemd-line # n950
In Linux distributions that use systemd, readahead binary (as part of the boot sequence) was replaced by systemd-readahead.[4][5] However, support for readahead was removed from systemd in its version 217, being described as unmaintained and unable to provide expected performance benefits
Should I install it from a previous debian version?
A instalação de um pacote a partir de uma distribuição anterior da Debian é possível usando a forma de fixar, mas isso não é recomendado.