linux-kernel - Re: [PATCH v2 0/7] mm: introduce shrinker debugfs interface

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Message-ID: <20220426183749.iumpdardzltpf23y@moria.home.lan>
Date:   Tue, 26 Apr 2022 14:37:49 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Dave Chinner <dchinner@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH v2 0/7] mm: introduce shrinker debugfs interface

On Tue, Apr 26, 2022 at 09:41:34AM -0700, Roman Gushchin wrote:
> My plan is to work on convert shrinkers API to bytes and experiment
> with different LRU implementations. I find an ability to easily export
> statistics and other data (which doesn't exist now) via debugfs useful
> (and way more convenient than changing existing tracepoints), as well as
> an ability to trigger scanning of individual shrinkers. If nobody else
> seeing any value here, I'm fine to keep these patches private, no reason
> to argue about the output format then.

I don't think converting the shrinker API to bytes instead of object counts is
such a great idea - that's going to introducing new rounding errors and new
corner cases when we can't free the exact # of bytes requested.

I was thinking along the lines of adding reporting for memory usage in bytes as
either an additional thing the .count_objects reports, or a new callback.