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    SubjectRe: [PATCH v10 12/14] mm: multi-gen LRU: debugfs interface
    On Fri, Apr 15, 2022 at 10:20 PM Andrew Morton
    <akpm@linux-foundation.org> wrote:
    >
    > On Fri, 15 Apr 2022 18:03:16 -0600 Yu Zhao <yuzhao@google.com> wrote:
    >
    > > > Presumably sysfs is the place. Fully documented and with usage
    > > > examples in the changelog so we can carefully review the proposed
    > > > extensions to Linux's ABI. Extensions which must be maintained
    > > > unchanged for all time.
    > >
    > > Eventually, yes. There still is a long way to go. Rest assured, this
    > > is something Google will keep investing resources on.
    >
    > So. The plan is to put these interfaces in debugfs for now, with a
    > view to migrating stabilized interfaces into sysfs (or procfs or
    > whatever) once end-user requirements and use cases are better
    > understood?

    The requirements are well understood and the use cases are proven,
    e.g., Google [1], Meta [2] and Alibaba [3].

    [1] https://dl.acm.org/doi/10.1145/3297858.3304053
    [2] https://dl.acm.org/doi/10.1145/3503222.3507731
    [3] https://gitee.com/anolis/cloud-kernel/blob/release-5.10/mm/kidled.c

    > If so, that sounds totally great to me. But it should have been in
    > the darn changelog! This is the sort of thing which we care about most
    > keenly.
    >
    > It would be helpful for reviewers to understand the proposed timeline
    > for this process, because the entire feature isn't really real until
    > this is completed, is it? I do think we should get this nailed down
    > relatively rapidly, otherwise people will be reluctant to invest much
    > into a moving target.
    >
    > And I must say, I see dissonance between the overall maturity of the
    > feature as described in these emails versus the immaturity of these
    > userspace control interfaces. What's happening there?

    Very observant. To answer both of the questions above: each iteration
    of the entire stack is a multi-year effort.

    Given its ROI, companies I know of constantly pour money into this
    area. Given its scale, this debugfs is the least of their concerns. A
    good example is the proactive reclaim sysfs interface [4]. It's been
    used at Google for many years and at Meta for a few years. We only
    started finalizing it recently.

    [4] https://lore.kernel.org/r/20220425190040.2475377-1-yosryahmed@google.com/

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