Apart from that, it's also not really a bad idea to write your own virtual memory management layer if you know you can do a better job than the OS because you k

Apart from that, it's also not really a bad idea to write your own virtual memory management layer if you know you can do a better job than the OS because you know much more about the expected access patterns, or because you know that the OS does a really bad job in some common cases. Sometimes, the OS is unable to handle large virtual memory areas (think OpenVZ/Virtuozzo VPS with 256MB RAM = virtual memory and 50GB of storage that now cannot be used in this way). Perhaps Squid didn't do such a good job, but just leaving everything to an idealized OS is short-sighted (as proven by the more recent Varnish code).