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[37.188.140.107]) by smtp.gmail.com with ESMTPSA id y20sm4703624wma.0.2020.03.20.00.28.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2020 00:28:21 -0700 (PDT) Date: Fri, 20 Mar 2020 08:28:20 +0100 From: Michal Hocko To: Matthew Wilcox Cc: Chris Down , qiwuchen55@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, chenqiwu Subject: Re: [PATCH] mm/vmscan: fix incorrect return type for cgroup_reclaim() Message-ID: <20200320072820.GA24409@dhcp22.suse.cz> References: <1584633026-26288-1-git-send-email-qiwuchen55@gmail.com> <20200319162025.GA237751@chrisdown.name> <20200319173606.GL22433@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200319173606.GL22433@bombadil.infradead.org> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 19-03-20 10:36:06, Matthew Wilcox wrote: > On Thu, Mar 19, 2020 at 04:20:25PM +0000, Chris Down wrote: [...] > > > -static bool cgroup_reclaim(struct scan_control *sc) > > > +static struct mem_cgroup *cgroup_reclaim(struct scan_control *sc) > > > { > > > - return false; > > > + return NULL; > > > } > > I think this is actually the important bit. For those who build > their kernels with cgroups disabled, it will save a small number of > instructions since cgroup_reclaim() will be NULL rather than dereferencing > sc->target_mem_group. It'd be nice to have that saving quantified as > part of the changelog. I gave it a try and you are right that !MEMCG is slightly better. But MEMCG=y which is a more common configuration I would say is worse text data bss dec hex filename 40661 24060 12 64733 fcdd mm/vmscan.memcg.after.o 40556 24060 12 64628 fc74 mm/vmscan.memcg.before.o 36240 23076 8 59324 e7bc mm/vmscan.nomemcg.after.o 36283 23076 8 59367 e7e7 mm/vmscan.nomemcg.before.o This is with gcc version 9.2.1 20200306 (Debian 9.2.1-31). -- Michal Hocko SUSE Labs