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Tue, 12 May 2020 10:42:31 +0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 04CAgThg62652518 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 May 2020 10:42:29 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B6EB5A4053; Tue, 12 May 2020 10:42:29 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6A65DA404D; Tue, 12 May 2020 10:42:27 +0000 (GMT) Received: from linux.vnet.ibm.com (unknown [9.126.150.29]) by d06av23.portsmouth.uk.ibm.com (Postfix) with SMTP; Tue, 12 May 2020 10:42:27 +0000 (GMT) Date: Tue, 12 May 2020 16:12:26 +0530 From: Srikar Dronamraju To: David Hildenbrand Subject: Re: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Message-ID: <20200512104226.GE1961@linux.vnet.ibm.com> References: <20200428165912.ca1eadefbac56d740e6e8fd1@linux-foundation.org> <20200429014145.GD19958@linux.vnet.ibm.com> <20200429122211.GD28637@dhcp22.suse.cz> <20200430071820.GF19958@linux.vnet.ibm.com> <20200504093712.GL22838@dhcp22.suse.cz> <20200508130304.GA1961@linux.vnet.ibm.com> <3bfe7469-1d8c-baa4-6d9d-f4786492eaa8@redhat.com> <20200511174731.GD1961@linux.vnet.ibm.com> <45d50d80-c998-9372-42eb-ca753a7258b9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <45d50d80-c998-9372-42eb-ca753a7258b9@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.676 definitions=2020-05-12_02:2020-05-11, 2020-05-12 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 clxscore=1015 phishscore=0 impostorscore=0 mlxscore=0 suspectscore=0 lowpriorityscore=0 adultscore=0 mlxlogscore=974 spamscore=0 bulkscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120077 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Srikar Dronamraju Cc: Linus Torvalds , linux-kernel@vger.kernel.org, Michal Hocko , linux-mm@kvack.org, Satheesh Rajendran , Mel Gorman , "Kirill A. Shutemov" , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Christopher Lameter , Vlastimil Babka Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" * David Hildenbrand [2020-05-12 09:49:05]: > On 11.05.20 19:47, Srikar Dronamraju wrote: > > * David Hildenbrand [2020-05-08 15:42:12]: > > > > > > [root@localhost ~]# cat /sys/devices/system/node/online > > 0 > > [root@localhost ~]# cat /sys/devices/system/node/possible > > 0-1 > > > > Even without my patch, both the combinations, I am still unable to see a > > cpuless, memoryless node being online. And the interesting part being even > > Yeah, I think on x86, all memory-less and cpu-less nodes are offline as > default. Especially when hotunplugging cpus/memory, we set them offline > as well. I also came to the same conclusion that we may not have a cpuless,memoryless node on x86. > > But as Michal mentioned, the node handling code is complicated and > differs between various architectures. > I do agree that node handling code differs across various architectures and quite complicated. > > if I mark node 0 as cpuless,memoryless and node 1 as actual node, the system > > somewhere marks node 0 as the actual node. > > Is the kernel maybe mapping PXM 1 to node 0 in that case, because it > always requires node 0 to be online/contain memory? Would be interesting > what happens if you hotplug a DIMM to (QEMU )node 0 - if PXM 0 will be > mapped to node 1 then as well. > Satheesh Rajendra had tried with cpu hotplug on a similar setup and we found that it crashes the x86 system. reference: https://bugzilla.kernel.org/show_bug.cgi?id=202187 Even if we were able to hotplug 1 DIMM memory into node 1, that would no more be a memoryless node. -- Thanks and Regards Srikar Dronamraju