linux-kernel - Re: [PATCH] mm: Make mem_cgroup_id_get_many dependent on MMU and MEMCG

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Message-ID: <20200305183426.GA752201@chrisdown.name>
Date:   Thu, 5 Mar 2020 18:34:26 +0000
From:   Chris Down <chris@...isdown.name>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Michal Hocko <mhocko@...nel.org>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: Make mem_cgroup_id_get_many dependent on MMU and
 MEMCG_SWAP

Johannes Weiner writes:
>I would ack a patch that adds __maybe_unused.
>
>This is a tiny function. If we keep it around a few releases after
>removing the last user, it costs us absolutely nothing. Eventually
>somebody will notice and send a patch to remove it. No big deal.
>
>There is, however, real cost in keeping bogus warnings around and
>telling people to ignore them. It's actively lowering the
>signal-to-noise ratio and normalizing warnings to developers. That's
>the kind of thing that will actually hide problems in the kernel.
>
>We know that the function can be unused in certain scenarios. It's
>silly to let the compiler continue to warn about it. That's exactly
>what __maybe_unused is for, so let's use it here.

Yeah, this is exactly what I was trying to express in the first one[0]. The 
fact that this patch came around a second time, as expected, just solidifies my 
concern around the waste to human time.

I would also ack a patch that adds __maybe_unused.

0: https://lore.kernel.org/linux-mm/20191217143720.GB131030@chrisdown.name/