How common is it for operating systems to do anything other than this: 1. Initially map the not-yet-written page to a read-only page full of zeros (the same on

How common is it for operating systems to do anything other than this: 1. Initially map the not-yet-written page to a read-only page full of zeros (the same one for all allocations: only one exists in the whole system). 2. When a write takes place, copy-on-write clone that page to a newly allocated zero-filled-page, then allow the write to proceed.