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    SubjectRe: [PATCH] only irq-safe atomic ops
    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.

    Steve



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