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SubjectRe: remove zero_page (was Re: -mm merge plans for 2.6.24)

On Wed, 3 Oct 2007, Nick Piggin wrote:
> I don't know if Linus actually disliked the patch itself, or disliked
> my (maybe confusingly worded) rationale?

Yes. I'd happily accept the patch, but I'd want it clarified and made
obvious what the problem was - and it wasn't the zero page itself, it was
a regression in the VM that made it less palatable.

I also thought that there were potentially better solutions, namely to
simply avoid the VM regression, but I also acknowledge that they may not
be worth it - I just want them to be on the table.

In short: the real cost of the zero page was the reference counting on the
page that we do these days. For example, I really do believe that the
problem could fairly easily be fixed by simply not considering zero_page
to be a "vm_normal_page()". We already *do* have support for pages not
getting ref-counted (since we need it for other things), and I think that
zero_page very naturally falls into exactly that situation.

So in many ways, I would think that turning zero-page into a nonrefcounted
page (the same way we really do have to do for other things anyway) would
be the much more *direct* solution, and in many ways the obvious one.

HOWEVER - if people think that it's easier to remove zero_page, and want
to do it for other reasons, *AND* can hopefully even back up the claim
that it never matters with numbers (ie that the extra pagefaults just make
the whole zero-page thing pointless), then I'd certainly accept the patch.

I'd just want the patch *description* to then also be correct, and blame
the right situation, instead of blaming zero-page itself.

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