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Shutemov" , Christopher Lameter , 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: <20200701100442.GB17918@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20200624092846.9194-1-srikar@linux.vnet.ibm.com> <20200624092846.9194-4-srikar@linux.vnet.ibm.com> <20200701084200.GN2369@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20200701084200.GN2369@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-07-01_04:2020-07-01,2020-07-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 clxscore=1015 suspectscore=0 mlxscore=0 adultscore=0 impostorscore=0 cotscore=-2147483648 spamscore=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2007010069 X-Rspamd-Queue-Id: 3B06718038E74 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: * Michal Hocko [2020-07-01 10:42:00]: > > > > > 2. Also existence of dummy node also leads to inconsistent information. The > > number of online nodes is inconsistent with the information in the > > device-tree and resource-dump > > > > 3. When the dummy node is present, single node non-Numa systems end up showing > > up as NUMA systems and numa_balancing gets enabled. This will mean we take > > the hit from the unnecessary numa hinting faults. > > I have to say that I dislike the node online/offline state and directly > exporting that to the userspace. Users should only care whether the node > has memory/cpus. Numa nodes can be online without any memory. Just > offline all the present memory blocks but do not physically hot remove > them and you are in the same situation. If users are confused by an > output of tools like numactl -H then those could be updated and hide > nodes without any memory&cpus. > > The autonuma problem sounds interesting but again this patch doesn't > really solve the underlying problem because I strongly suspect that the > problem is still there when a numa node gets all its memory offline as > mentioned above. > > While I completely agree that making node 0 special is wrong, I have > still hard time to review this very simply looking patch because all the > numa initialization is so spread around that this might just blow up > at unexpected places. IIRC we have discussed testing in the previous > version and David has provided a way to emulate these configurations > on x86. Did you manage to use those instruction for additional testing > on other than ppc architectures? > I have tried all the steps that David mentioned and reported back at https://lore.kernel.org/lkml/20200511174731.GD1961@linux.vnet.ibm.com/t/#u As a summary, David's steps are still not creating a memoryless/cpuless on x86 VM. I have tried booting with Numa/non-numa on all the x86 machines that I could get to. -- Thanks and Regards Srikar Dronamraju