From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e39.co.us.ibm.com (e39.co.us.ibm.com [32.97.110.160]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3AF401A0362 for ; Fri, 20 Jun 2014 03:14:42 +1000 (EST) Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 19 Jun 2014 11:14:36 -0600 Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 29099C40029 for ; Thu, 19 Jun 2014 11:14:22 -0600 (MDT) Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by b03cxnp07029.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s5JFArdZ66519080 for ; Thu, 19 Jun 2014 17:10:53 +0200 Received: from d03av03.boulder.ibm.com (localhost [127.0.0.1]) by d03av03.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s5JHEK0o007234 for ; Thu, 19 Jun 2014 11:14:22 -0600 Date: Thu, 19 Jun 2014 10:14:01 -0700 From: Nishanth Aravamudan To: Tejun Heo Subject: Re: Node 0 not necessary for powerpc? Message-ID: <20140619171401.GU16644@linux.vnet.ibm.com> References: <20140311195632.GA946@linux.vnet.ibm.com> <20140313164949.GC22247@linux.vnet.ibm.com> <20140519182400.GM8941@linux.vnet.ibm.com> <20140521185812.GA5259@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140521185812.GA5259@htj.dyndns.org> Cc: tony.luck@intel.com, linux-mm@kvack.org, anton@samba.org, David Rientjes , Christoph Lameter , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 21.05.2014 [14:58:12 -0400], Tejun Heo wrote: > Hello, > > On Wed, May 21, 2014 at 09:16:27AM -0500, Christoph Lameter wrote: > > On Mon, 19 May 2014, Nishanth Aravamudan wrote: > > > I'm seeing a panic at boot with this change on an LPAR which actually > > > has no Node 0. Here's what I think is happening: > > > > > > start_kernel > > > ... > > > -> setup_per_cpu_areas > > > -> pcpu_embed_first_chunk > > > -> pcpu_fc_alloc > > > -> ___alloc_bootmem_node(NODE_DATA(cpu_to_node(cpu), ... > > > -> smp_prepare_boot_cpu > > > -> set_numa_node(boot_cpuid) > > > > > > So we panic on the NODE_DATA call. It seems that ia64, at least, uses > > > pcpu_alloc_first_chunk rather than embed. x86 has some code to handle > > > early calls of cpu_to_node (early_cpu_to_node) and sets the mapping for > > > all CPUs in setup_per_cpu_areas(). > > > > Maybe we can switch ia64 too embed? Tejun: Why are there these > > dependencies? > > > > > Thoughts? Does that mean we need something similar to x86 for powerpc? > > I'm missing context to properly understand what's going on but the > specific allocator in use shouldn't matter. e.g. x86 can use both > embed and page allocators. If the problem is that the arch is > accessing percpu memory before percpu allocator is initialized and the > problem was masked before somehow, the right thing to do would be > removing those premature percpu accesses. If early percpu variables > are really necessary, doing similar early_percpu thing as in x86 would > be necessary. The early access is in the arch's pcpu_alloc_bootmem. On x86, rather than using NODE_DATA(cpu_to_node), it uses (in pcpu_alloc_bootmem), early_cpu_to_node(cpu) with their custom logic. The issue is that cpu_to_node, if USE_PERCPU_NUMA_NODE_ID is defined (which it is for NUMA powerpc, x86, ia64), is that cpu_to_node uses the percpu area, which data isn't initialized yet. So I guess powerpc needs the same treatment as x86. Thanks, Nish