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[37.188.254.25]) by smtp.gmail.com with ESMTPSA id o3sm31430395wme.36.2020.03.16.01.54.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2020 01:54:27 -0700 (PDT) Date: Mon, 16 Mar 2020 09:54:25 +0100 From: Michal Hocko To: Christopher Lameter Cc: Srikar Dronamraju , Andrew Morton , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Vlastimil Babka , "Kirill A. Shutemov" , Linus Torvalds Subject: Re: [PATCH 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Message-ID: <20200316085425.GB11482@dhcp22.suse.cz> References: <20200311110237.5731-1-srikar@linux.vnet.ibm.com> <20200311110237.5731-4-srikar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Sun 15-03-20 14:20:05, Cristopher Lameter wrote: > On Wed, 11 Mar 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. > > Would it not be better and simpler to require that node 0 always has > memory (and processors)? A mininum operational set? I do not think you can simply ignore the reality. I cannot say that I am a fan of memoryless/cpuless numa configurations but they are a sad reality of different LPAR configurations. We have to deal with them. Besides that I do not really see any strong technical arguments to lack a support for those crippled configurations. We do have zonelists that allow to do reasonable decisions on memoryless nodes. So no, I do not think that this is a viable approach. > We can dynamically number the nodes right? So just make sure that the > firmware properly creates memory on node 0? Are you suggesting that the OS would renumber NUMA nodes coming from FW just to satisfy node 0 existence? If yes then I believe this is really a bad idea because it would make HW/LPAR configuration matching to the resulting memory layout really hard to follow. -- Michal Hocko SUSE Labs