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    SubjectRe: [PATCH] only irq-safe atomic ops
    Stephen Lord wrote:
    >
    > Andrew Morton wrote:
    >
    > >Robert Love wrote:
    > >
    > >>...
    > >>
    > >>Question: if (from below) you are going to use atomic operations, why
    > >>make it per-CPU at all? Just have one counter and atomic_inc and
    > >>atomic_read it. You won't need a spin lock.
    > >>
    > >
    > >Oh that works fine. But then it's a global counter, so each time
    > >a CPU marks a page dirty, the counter needs to be pulled out of
    > >another CPU's cache. Which is not a thing I *need* to do.
    > >
    > >As I said, it's a micro-issue. But it's a requirement which
    > >may pop up elsewhere.
    > >
    > >
    > I can tell you that Irix has just such a global counter for the amount of
    > delayed allocate pages - and it gets to be a major point of cache contention
    > once you get to larger cpu counts. So avoiding that from the start would
    > be good.

    Ah, good info. Thanks. I'll fix it with a big "FIXME" comment for now,
    fix it for real when Rusty's per-CPU infrastructure appears.

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