linux-kernel - Re: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers

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Message-ID: <20231003130324.GC17012@cmpxchg.org>
Date:   Tue, 3 Oct 2023 09:03:24 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Michal Koutný <mkoutny@...e.com>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: memcg: refactor page state unit helpers

On Fri, Sep 22, 2023 at 05:57:39PM +0000, Yosry Ahmed wrote:
> memcg_page_state_unit() is currently used to identify the unit of a
> memcg state item so that all stats in memory.stat are in bytes. However,
> it lies about the units of WORKINGSET_* stats. These stats actually
> represent pages, but we present them to userspace as a scalar number of
> events. In retrospect, maybe those stats should have been memcg "events"
> rather than memcg "state".
> 
> In preparation for using memcg_page_state_unit() for other purposes that
> need to know the truthful units of different stat items, break it down
> into two helpers:
> - memcg_page_state_unit() retuns the actual unit of the item.
> - memcg_page_state_output_unit() returns the unit used for output.
> 
> Use the latter instead of the former in memcg_page_state_output() and
> lruvec_page_state_output(). While we are at it, let's show cgroup v1
> some love and add memcg_page_state_local_output() for consistency.
> 
> No functional change intended.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

That's a nice cleanup in itself.

Acked-by: Johannes Weiner <hannes@...xchg.org>