A page-table entry (PTE) is relatively small, requiring just eight bytes to refer to a
4096-byte page on most systems. It thus does not seem like a worrisome
level of overhead, and little effort has been made over the kernel’s
history to reduce page-table memory consumption. Those eight bytes can
hurt, though, if they are replicated across a sufficiently large set of
processes. The msharefs
patch set from Khalid Aziz is a revised attempt to address that
problem, but it is proving to be a hard sell in the memory-management
community.

Source: LWN.net – [$] Sharing page tables with msharefs