From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58C75C3F2D2 for ; Thu, 5 Mar 2020 16:21:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 317B820637 for ; Thu, 5 Mar 2020 16:21:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726674AbgCEQVK (ORCPT ); Thu, 5 Mar 2020 11:21:10 -0500 Received: from foss.arm.com ([217.140.110.172]:50780 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726177AbgCEQVK (ORCPT ); Thu, 5 Mar 2020 11:21:10 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 44C6630E; Thu, 5 Mar 2020 08:21:09 -0800 (PST) Received: from [10.37.12.159] (unknown [10.37.12.159]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F15DD3F534; Thu, 5 Mar 2020 08:21:07 -0800 (PST) Subject: Re: [PATCH] mm: Make mem_cgroup_id_get_many dependent on MMU and MEMCG_SWAP To: Johannes Weiner Cc: Michal Hocko , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vladimir Davydov , Andrew Morton References: <20200304142348.48167-1-vincenzo.frascino@arm.com> <20200304165336.GO16139@dhcp22.suse.cz> <8c489836-b824-184e-7cfe-25e55ab73000@arm.com> <20200305160929.GA1166@cmpxchg.org> From: Vincenzo Frascino Message-ID: Date: Thu, 5 Mar 2020 16:21:28 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200305160929.GA1166@cmpxchg.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Johannes, On 3/5/20 4:09 PM, Johannes Weiner wrote: > On Thu, Mar 05, 2020 at 09:49:23AM +0000, 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. > > 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. > I agree with what you are saying. I am going to change my patch accordingly. Thank you. -- Regards, Vincenzo