> What's not helping the situation is the fact that the kernel has no good page allocation API that differentiates between reserving and committing memory.

mmap with PROT_NONE is such a reservation and doesn't count towards the commit limit. A later mmap with MAP_FIXED and PROT_READ | PROT_WRITE can commit parts of the reserved region, and mmap calls with PROT_NONE and MAP_FIXED will decommit.