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    SubjectRe: [PATCH] Cpuset: rcu optimization of page alloc hook
    Paul Jackson <pj@sgi.com> wrote:
    >
    > > Please do use __read_mostly for new kmem_cache :
    > >
    > > static kmem_cache_t *cpuset_cache __read_mostly;
    >
    > Is there any downside to this? I ask because accesses through
    > this 'cpuset_cache' pointer are rather infrequent - only when
    > the sysadmin or the batch scheduler is creating or removing
    > cpusets, which for the purposes of 'back of the envelope'
    > estimates, might be once a minute or less. Further, it is
    > not at all a performance critical path.
    >
    > So I really don't give a dang if it takes a few milliseconds
    > to pick up this pointer, at least so far as cpusets matters.

    There's no downside, really. It just places the storage into a different
    section. There's a small downside to having __read_mostly at all: up to a
    page more memory used. But once it's there, adding to it is just moving
    things around in memory.

    __read_mostly is simply a new (page-aligned) section into we put things
    which are considered to not be written to very often.

    > That said, would you still advise marking this __read_mostly?

    Not at this stage - it'd be better if someone did a big sweep and changed
    all kmem_cache_t's in one hit.

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