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    SubjectRe: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers
    On Wed, Oct 04, 2023 at 02:36:19PM -0400, Johannes Weiner <hannes@cmpxchg.org> wrote:
    > Yes, it's because of node resolution which event counters generally
    > don't have. Some of the refault events influence node-local reclaim
    > decisions, see mm/vmscan.c::snapshot_refaults().
    >
    > There are a few other event counters in the stat array that people
    > thought would be useful to have split out in
    > /sys/devices/system/node/nodeN/vmstat to understand numa behavior
    > better.
    >
    > It's a bit messy.
    >
    > Some events would be useful to move to 'stats' for the numa awareness,
    > such as the allocator stats and reclaim activity.
    >
    > Some events would be useful to move to 'stats' for the numa awareness,
    > but don't have the zone resolution required by them, such as
    > kswapd/kcompactd wakeups.

    Thanks for the enlightenment.

    > Some events aren't numa specific, such as oom kills, drop_pagecache.

    These are oddballs indeed. As with the normalization patchset these are
    counted as PAGE_SIZE^W 1 error but they should rather be an infinite
    error (to warrant a flush).

    So my feedback to this series is:
    - patch 1/2 -- creating two classes of units is consequence of unclarity
    between state and events (as in event=Δstate/Δt) and resolution
    (global vs per-node), so the better approach would be to tidy this up,
    - patch 2/2 -- it could use the single unit class that exists,
    it'll bound the error of printed numbers afterall (and can be changed
    later depending on how it affects internal consumers).

    My 0.02€,
    Michal
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