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    SubjectRe: [PATCH UPDATED] percpu: use dynamic percpu allocator as the default percpu allocator
    On Thu, 2 Apr 2009, Ingo Molnar wrote:

    > to quote an earlier part of my mail:
    > > > We encourage kfree(NULL) and it triggers commonly in the kernel
    > > > today [on distro kernels we checked it can trigger once per
    > > > syscall!] - so i think we should consider free_percpu(NULL) a
    > > > possibly common pattern too. (even though today it's likely
    > > > _not_ common at all.)
    > I specifically mentioned that it is not at all common now.

    What is this? Nonsense day? Consider it a common pattern although its
    likely not common at all? April fools day?

    > But there's no reason why an object shutdown fastpath with an
    > optional percpu buffer (say for debug statistics, not enabled by
    > default) couldnt look like this:
    > percpu_free(NULL);
    > We actually have such patterns of kfree(ptr) use, where the _common_
    > case in a fastpath is kfree(NULL).

    Speculation. A shutdown fastpath? The percpu allocation and free
    operations are expensive and deal with teardown and setup of virtual
    mappings. Those paths are *not* optimized for fastpath use. kfree is

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