> The seemingly critical parallel job performance issue sounds like it can and should be handled transparently by the OS when multiple pages are involved,

A thread can only fault on one page at a time, and only sequential access patterns can benefit from the OS bringing in multiple pages per fault. Having all of your CPU cores busy handling page faults and context switches to threads that are about to trigger another page fault is only going to generate enough read traffic to keep a few SSDs busy, not a full shelf of 24+ drives. mmap() and synchronous IO don't scale well enough for today's SSDs.