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[37.188.168.3]) by smtp.gmail.com with ESMTPSA id q3sm2881770eds.41.2020.07.01.05.23.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 05:23:54 -0700 (PDT) Date: Wed, 1 Jul 2020 14:23:53 +0200 From: Michal Hocko To: Srikar Dronamraju Cc: Christopher Lameter , Andrew Morton , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Vlastimil Babka , "Kirill A. Shutemov" , Michael Ellerman , Linus Torvalds , Gautham R Shenoy , Satheesh Rajendran , David Hildenbrand Subject: Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Message-ID: <20200701122353.GU2369@dhcp22.suse.cz> References: <20200624092846.9194-1-srikar@linux.vnet.ibm.com> <20200624092846.9194-4-srikar@linux.vnet.ibm.com> <20200630040125.GA31617@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200630040125.GA31617@linux.vnet.ibm.com> X-Rspamd-Queue-Id: 9AF8D3761C X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 Tue 30-06-20 09:31:25, Srikar Dronamraju wrote: > * Christopher Lameter [2020-06-29 14:58:40]: > > > On Wed, 24 Jun 2020, Srikar Dronamraju wrote: > > > > > Currently Linux kernel with CONFIG_NUMA on a system with multiple > > > possible nodes, marks node 0 as online at boot. However in practice, > > > there are systems which have node 0 as memoryless and cpuless. > > > > Maybe add something to explain why you are not simply mapping the > > existing memory to NUMA node 0 which is after all just a numbering scheme > > used by the kernel and can be used arbitrarily? > > > > I thought Michal Hocko already gave a clear picture on why mapping is a bad > idea. https://lore.kernel.org/lkml/20200316085425.GB11482@dhcp22.suse.cz/t/#u > Are you suggesting that we add that as part of the changelog? Well, I was not aware x86 already does renumber. So there is a certain precendence. As I've said I do not really like that but this is what already is happening. If renumbering is not an option then just handle that in the ppc code explicitly. Generic solution would be preferable of course but as I've said it is really hard to check for correctness and potential subtle issues. -- Michal Hocko SUSE Labs