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    SubjectRe: [PATCH 06/43] mm: numa: Make pte_numa() and pmd_numa() a generic implementation
    On Fri, Nov 16, 2012 at 07:04:04PM +0100, Ingo Molnar wrote:
    >
    > * Mel Gorman <mgorman@suse.de> wrote:
    >
    > > That said, your approach just ends up being heavier. [...]
    >
    > Well, it's more fundamental than just whether to inline or not
    > (which I think should be a separate optimization and I won't
    > object to two-instruction variants the slightest) - but you
    > ended up open-coding change_protection()
    > via:
    >
    > change_prot_numa_range() et al
    >
    > which is a far bigger problem...
    >
    > Do you have valid technical arguments in favor of that
    > duplication?
    >

    No, I don't and I have not claimed that it *has* to exist. In fact I've
    said multiple times than I can convert to change_protection as long as
    _PAGE_NUMA == _PAGE_NONE. This initial step was to build the list
    of requirements without worrying about breaking existing users of
    change_protection. Now that I know what the requirements are, I can convert.

    > If you just embrace the PROT_NONE reuse approach of numa/core
    > then 90% of the differences in your tree will disappear and
    > you'll have a code base very close to where numa/core was 3
    > weeks ago already, modulo a handful of renames.
    >

    Pointed out the missing parts in another mail already -- MIGRATE_FAULT,
    pmd handling in batch, stats and a logical progression from a simple to
    a complex policy.

    > It's not like PROT_NONE will go away anytime soon.
    >
    > PROT_NONE is available on every architecture, and we use the
    > exact semantics of it in the scheduler, we just happen to drive
    > it from a special worklet instead of a syscall, and happen to
    > have a callback to the faults when they happen...
    >
    > Please stay open to that approach.
    >

    I will.

    If anything, me switching to prot_none would be a hell of a lot easier
    than you trying to pick up the bits you're missing. I'll take a look
    Monday and see what falls out.

    --
    Mel Gorman
    SUSE Labs


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