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

    On Tue, 9 Oct 2007, Nick Piggin wrote:
    > I gave 2 other numbers. After that, it really doesn't matter if I give
    > you 2 numbers or 200, because it wouldn't change the fact that there
    > are 3 programs using the ZERO_PAGE that we'll never know about.

    You gave me no timings what-so-ever. Yes, you said "1000 page faults", but
    no, I have yet to see a *single* actual performance number.

    Maybe I missed it? Or maybe you just never did them.

    Was it really so non-obvious that I actually wanted *performance* numbers,
    not just some random numbers about how many page faults you have? Or did
    you post them somewhere else? I don't have any memory of having seen any
    performance numbers what-so-ever, but I admittedly get too much email.

    Here's three numbers of my own: 8, 17 and 975.

    So I gave you "numbers", but what do they _mean_?

    So let me try one more time:

    - I don't want any excuses about how bad PAGE_ZERO is. You made it bad,
    it wasn't bad before.
    - I want numbers. I want the commit message to tell us *why* this is
    done. The numbers I want is performance numbers, not handwave numbers.
    Both for the bad case that it's supposed to fix, *and* for "normal
    - I want you to just say that if it turns out that there are people who
    use ZERO_PAGE, you stop calling them crazy, and promise to look at the

    How much clearer can I be? I have said several times that I think this
    patch is kind of sad, and the reason I think it's sad is that you (and
    Hugh) convinced me to take the patch that made it sad in the first place.
    It didn't *use* to be bad. And I've use ZERO_PAGE myself for timing, I've
    had nice test-programs that knew that it could ignore cache effects and
    get pure TLB effects when it just allocated memory and didn't write to it.

    That's why I don't like the lack of numbers. That's why I didn't like the
    original commit message that tried to blame the wrong part. That's why I
    didn't like this patch to begin with.

    But I'm perfectly ready to take it, and see if anybody complains.
    Hopefully nobody ever will.

    But by now I absolutely *detest* this patch because of its history, and
    how I *told* you guys what the reserved bit did, and how you totally
    ignored it, and then tried to blame ZERO_PAGE for that. So yes, I want the
    patch to be accompanied by an explanation, which includes the performance
    side of why it is wanted/needed in the first place.

    If this patch didn't have that kind of history, I wouldn't give a flying f
    about it. As it is, this whole thing has a background.

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