linux-kernel - Re: [PATCH 0/9] mm/damon: let users feed and tame/auto-tune DAMOS

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Date:   Thu, 30 Nov 2023 14:22:58 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        David Gow <davidgow@...gle.com>, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] mm/damon: let users feed and tame/auto-tune DAMOS

On Thu, 30 Nov 2023 02:36:43 +0000 SeongJae Park <sj@...nel.org> wrote:

> The core logic uses the below simple feedback loop algorithm to
> calculate the next aggressiveness level of the scheme from the current
> aggressiveness level and the current feedback (target_score and
> current_score).  It calculates the compensation for next aggressiveness
> as a proportion of current aggressiveness and distance to the target
> score.  As a result, it arrives at the near-goal state in a short time
> using big steps when it's far from the goal, but avoids making
> unnecessarily radical changes that could turn out to be a bad decision
> using small steps when its near to the goal.

fwiw, the above is a "proportional controller".  MGLRU has, in
vmscan.c, a PID controller (proportional, integral, derivative).  PID
controllers have better accuracy (the integral feedback) and better
stability (the derivative feedback).

Generalizing MGLRU's PID controller might be somewhat challenging!