> I disagree with this ... why shouldn't zero filled memory be backed with
> just *one* by all processes shared R/O page when it faults for reading that
> uses copy-on-write to get a private one if something changed ?

If you want to investigate this, you really need to measure the result
on real workloads.

My gut feel here is that you'll discover that, in practice, most ZFOD
pages are written shortly after they are touched for the first time,
and this "optimization" would save very little memory and consume lots
of extra cpu; the "COW" fault would also require a TLB shootdown on
multiprocessor systems whereas touching an previously unmapped page
does not require TLB invalidation (since there can't be a previous
live TLB entry).

					- Bill