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

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Date:   Thu, 5 Mar 2020 11:00:23 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.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

On Thu 05-03-20 09:49:23, Vincenzo Frascino wrote:
> Hi Michal,
> 
> On 3/4/20 4:53 PM, Michal Hocko wrote:
> > On Wed 04-03-20 14:23:48, Vincenzo Frascino wrote:
> >> mem_cgroup_id_get_many() is currently used only when MMU or MEMCG_SWAP
> >> configuration options are enabled. Having them disabled triggers the
> >> following warning at compile time:
> >>
> >> linux/mm/memcontrol.c:4797:13: warning: ‘mem_cgroup_id_get_many’ defined
> >> but not used [-Wunused-function]
> >>  static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned
> >>  int n)
> >>
> >> Make mem_cgroup_id_get_many() dependent on MMU and MEMCG_SWAP to address
> >> the issue.
> > 
> > A similar patch has been proposed recently
> > http://lkml.kernel.org/r/87fthjh2ib.wl-kuninori.morimoto.gx@renesas.com.
> > The conclusion was that the warning is not really worth adding code.
> > 
> 
> Thank you for pointing this out, I was not aware of it. I understand that you
> are against "#ifdeffery" in this case, but isn't it the case of adding at least
> __maybe_unused? This would prevent people from reporting it over and over again
> and you to have to push them back :) Let me know what do you think, in case I am
> happy to change my patch accordingly.

We have discussed __maybe_unused in the email thread as well. I am not a
great fan of that as mentioed there.
-- 
Michal Hocko
SUSE Labs