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b=IE1pXpb7tEtDPJb1XPIB8Qu0S2GzmepwH2QCl5imqd4uVrjQ6FOIaKUEilPkEvxvf 8xkpZBwuPD2joCO0YlGF61cyqD55UJYIV8W9ya1CD5oXdVR7zS/ZCbPF3+6GNnNTGc pey9QOPoFuxqaAqcT4v1qyyDZDa+7k3k4RllX9m0= Date: Wed, 13 Mar 2024 08:51:44 -0700 From: Andrew Morton To: "Huang, Ying" Cc: Donet Tom , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Aneesh Kumar , Michal Hocko , Dave Hansen , Mel Gorman , Feng Tang , Andrea Arcangeli , Peter Zijlstra , Ingo Molnar , Rik van Riel , Johannes Weiner , Matthew Wilcox , Vlastimil Babka , Dan Williams , Hugh Dickins , Kefeng Wang , Suren Baghdasaryan Subject: Re: [PATCH v2 2/2] mm/numa_balancing:Allow migrate on protnone reference with MPOL_PREFERRED_MANY policy Message-Id: <20240313085144.13b37a79c688b6126af0bd07@linux-foundation.org> In-Reply-To: <874jdd5z1b.fsf@yhuang6-desk2.ccr.corp.intel.com> References: <369d6a58758396335fd1176d97bbca4e7730d75a.1709909210.git.donettom@linux.ibm.com> <874jdd5z1b.fsf@yhuang6-desk2.ccr.corp.intel.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C034540005 X-Rspam-User: X-Stat-Signature: bn7jkoh8oapxz35xnr1hxni9qjn1ywqo X-Rspamd-Server: rspam01 X-HE-Tag: 1710345110-669713 X-HE-Meta: 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 /MUJPwAj aTchIicEp922XN379cWZQ+5x6+R2DLCv8YyH/YnVYfJBaWL4HreYfWj+gKNDpLplgvNzfiKZ7zy+RNKPJUhe+hcU1kkb+1E15T+34hF0izo/JSX1PFwsCkq/qhABVihHJ5r/xkKCLh3n52EK9cT9gjjvbdNBUBmfubogKGKJ4jvQ4SxK4eIAgeUiYPeZnO62/Tcv0mGN+reYNU6HcTv0eyC1ky+6ALS/eameT/DCvi605lq/J6e5zcUrbMJOqSaMOiAFsM9dvwlZmpA8sNxWd6E89EEMx10pQO6GeAhPpt5V+n2s= 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: List-Subscribe: List-Unsubscribe: On Mon, 11 Mar 2024 09:37:36 +0800 "Huang, Ying" wrote: > > @@ -2515,15 +2516,26 @@ int mpol_misplaced(struct folio *folio, struct vm_fault *vmf, > > break; > > > > case MPOL_BIND: > > - /* Optimize placement among multiple nodes via NUMA balancing */ > > + case MPOL_PREFERRED_MANY: > > + /* > > + * Even though MPOL_PREFERRED_MANY can allocate pages outside > > + * policy nodemask we don't allow numa migration to nodes > > + * outside policy nodemask for now. This is done so that if we > > + * want demotion to slow memory to happen, before allocating > > + * from some DRAM node say 'x', we will end up using a > > + * MPOL_PREFERRED_MANY mask excluding node 'x'. In such scenario > > + * we should not promote to node 'x' from slow memory node. > > + */ > > This is a little hard to digest for me. And, I don't think that we need > to put this policy choice in code comments. It's better to put it in > patch description. Where we can give more background, for example, to > avoid cross-socket traffic, etc. Oh. I like the comment. We could perhaps put additional detail in the changelog, but using changelogs to understand the code is so darned inconvenient.