I don't see how const would save memory, unless you have a separate ROM region that keeps that out of the main memory.

VMM. const memory can just be evicted and be swapped back in with zero cost. rw memory must be backed somehow, which us much more expensive.

I submitted a patch

Not true unless you actively modify it (or the page it was in). "RW" mapped memory that is not dirty is also discarded on memory pressure.