From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oa0-f45.google.com (mail-oa0-f45.google.com [209.85.219.45]) by kanga.kvack.org (Postfix) with ESMTP id B9DE86B0035 for ; Thu, 13 Mar 2014 12:49:12 -0400 (EDT) Received: by mail-oa0-f45.google.com with SMTP id o6so1342949oag.18 for ; Thu, 13 Mar 2014 09:49:12 -0700 (PDT) Received: from e7.ny.us.ibm.com (e7.ny.us.ibm.com. [32.97.182.137]) by mx.google.com with ESMTPS id uv2si3081755obb.19.2014.03.13.09.49.11 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 13 Mar 2014 09:49:12 -0700 (PDT) Received: from /spool/local by e7.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 13 Mar 2014 12:49:10 -0400 Received: from b01cxnp22033.gho.pok.ibm.com (b01cxnp22033.gho.pok.ibm.com [9.57.198.23]) by d01dlp03.pok.ibm.com (Postfix) with ESMTP id 34BC2C90041 for ; Thu, 13 Mar 2014 12:49:04 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by b01cxnp22033.gho.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s2DGn7pC3604932 for ; Thu, 13 Mar 2014 16:49:07 GMT Received: from d01av02.pok.ibm.com (localhost [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s2DGn6Hu022591 for ; Thu, 13 Mar 2014 12:49:07 -0400 Date: Thu, 13 Mar 2014 09:48:49 -0700 From: Nishanth Aravamudan Subject: Re: Node 0 not necessary for powerpc? Message-ID: <20140313164849.GB22247@linux.vnet.ibm.com> References: <20140311195632.GA946@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, anton@samba.org, cl@linux.com, benh@kernel.crashing.org On 11.03.2014 [19:02:17 -0700], David Rientjes wrote: > On Tue, 11 Mar 2014, Nishanth Aravamudan wrote: > > > I have a P7 system that has no node0, but a node0 shows up in numactl > > --hardware, which has no cpus and no memory (and no PCI devices): > > > > numactl --hardware > > available: 4 nodes (0-3) > > node 0 cpus: > > node 0 size: 0 MB > > node 0 free: 0 MB > > node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 > > node 1 size: 0 MB > > node 1 free: 0 MB > > node 2 cpus: > > node 2 size: 7935 MB > > node 2 free: 7716 MB > > node 3 cpus: > > node 3 size: 8395 MB > > node 3 free: 8015 MB > > node distances: > > node 0 1 2 3 > > 0: 10 20 10 20 > > 1: 20 10 20 20 > > 2: 10 20 10 20 > > 3: 20 20 20 10 > > > > This is because we statically initialize N_ONLINE to be [0] in > > mm/page_alloc.c: > > > > [N_ONLINE] = { { [0] = 1UL } }, > > > > I'm not sure what the architectural requirements are here, but at least > > on this test system, removing this initialization, it boots fine and is > > running. I've not yet tried stress tests, but it's survived the > > beginnings of kernbench so far. > > > > numactl --hardware > > available: 3 nodes (1-3) > > node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 > > node 1 size: 0 MB > > node 1 free: 0 MB > > node 2 cpus: > > node 2 size: 7935 MB > > node 2 free: 7479 MB > > node 3 cpus: > > node 3 size: 8396 MB > > node 3 free: 8375 MB > > node distances: > > node 1 2 3 > > 1: 10 20 20 > > 2: 20 10 20 > > 3: 20 20 10 > > > > Perhaps we could put in a ARCH_DOES_NOT_NEED_NODE0 and only define it on > > powerpc for now, conditionalizing the above initialization on that? > > > > I don't know if anything has recently changed in the past year or so, but > I've booted x86 machines with a hacked BIOS so that all memory on node 0 > is hotpluggable and offline, so I believe this is possible on x86 as well. Good to know, thanks! This is also certainly not very common on powerpc, but it is possible -- and the topology ends up being inaccurate because of the static initialization. Thanks, Nish -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org