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Wed, 8 Oct 2025 06:05:36 +0000 (GMT) Date: Wed, 8 Oct 2025 08:05:35 +0200 From: Sumanth Korikkar To: David Hildenbrand Cc: Andrew Morton , linux-mm , LKML , linux-s390 , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev Subject: Re: [PATCH 0/4] Support dynamic (de)configuration of memory Message-ID: References: <20250926131527.3260733-1-sumanthk@linux.ibm.com> <5e3b16ec-9ef9-483e-b97e-bff0c1915b19@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5e3b16ec-9ef9-483e-b97e-bff0c1915b19@redhat.com> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 6fWQ4SnX9jmxmfjEemvFmoq18YJ7A2AG X-Proofpoint-ORIG-GUID: 6fWQ4SnX9jmxmfjEemvFmoq18YJ7A2AG X-Authority-Analysis: v=2.4 cv=Fec6BZ+6 c=1 sm=1 tr=0 ts=68e5ff36 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=gABlUkJTZVALj7I02CYA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDA0MDAyMiBTYWx0ZWRfX3bFbGwH8kkF8 80trDb1rC5iYBgYASeHI/HLWMcllw2srfs7nRGTGILHE6p7L9VbeC/5ldO3K0ITSL7elSQHTAHs oHxhsMuEHMGrVYlwZJvk5QvLHEGkK+HISwJ5UgOfdKU1+d9U5w7mFRG27dtWOpasyjEeSk0SCd/ xD4B0vHa9ZJ9QmXz3Q5I/vEiuxDwvVojeZoEZl8uMUyFDijfA7/4Lw6QCaHwY8NyALdnirxXv2G P+jRPG+Qica+DzpNMOMUvl5Di5fugpcUMOHS31aByL2WGV5eYzbcPMYTkmD7WCA2E7d5sOEko/K pdPzesTu2evT+rD8oCmzBGY8MvuwrfzVv1hXdnT0uXwK5GK5pTqezo4z6j5y9l1wcTYE5oYn/5p LQmd28qZ+k9VDLGdvWTwFOH83WXxMg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-07_02,2025-10-06_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 impostorscore=0 suspectscore=0 spamscore=0 adultscore=0 clxscore=1015 malwarescore=0 priorityscore=1501 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2509150000 definitions=main-2510040022 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 698E0160008 X-Stat-Signature: 4ykhf4cwao5h1iy9n3m4fhxw4k9nqdz7 X-HE-Tag: 1759903544-593879 X-HE-Meta: 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 vl6OBMJ/ VvoJQT/PUY/qt8uApUOr0Etx1O3nis8Y0xfhyPlxTT4/BjnO5YbcaXWocMFwoGL3MCGeMPJN9u+9m8xAcctXqwRIpXYEValSx3bzfmPC+g9glfbHL0pm1CwYsMYVMmFgTUUIhuC6xVKyaw8wgWiXq3fG4WakG2x6xUb68/e+6d/LNsHXymV0WROQeuCzo2LiMFL+IMEArkFi5KVT85EvsEiBoxSfoTZofXye5QR49Gsq2kdSSWo2gkwFPb73E/diCAHCF 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: List-Subscribe: List-Unsubscribe: > Care to share an example output? I only have a s390x VM with 2 CPUs and no > way to configure/deconfigure. lscpu -e CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS 0 0 0 0 0 0 0:0:0 yes yes vert-medium 0 1 0 0 0 0 0 1:1:1 yes yes vert-medium 1 2 0 0 0 0 1 2:2:2 yes yes vert-low 2 3 0 0 0 0 1 3:3:3 yes yes vert-low 3 # chcpu -d 2-3 CPU 2 disabled CPU 3 disabled # chcpu -g 2 CPU 2 deconfigured # chcpu -c 2 CPU 2 configured # chcpu -e 2-3 CPU 2 enabled CPU 3 enabled > > chmem changes would look like: > > chmem -c 128M -m 1 : configure memory with memmap-on-memory enabled > > chmem -g 128M : deconfigure memory > > I wonder if the above two are really required. I would expect most/all users > to simply keep using -e / -d. > > Sure, there might be some corner cases, but I would assume most people to > not want to care about memmap-on-memory with the new model. I believe this remains very beneficial for customers in the following scenario: 1) Initial memory layout: 4 GB configured online 512 GB standby If memory_hotplug.memmap_on_memory=Y is set in the kernel command line: Suppose user requires more memory and onlines 256 GB. With memmap-on-memory enabled, this likely succeeds by default. Later, the user needs 256 GB of contiguous physical memory across memory blocks. Then, the user can still configure those memory blocks with memmap-on-memory disabled and online it. 2) If the administrator forgets to configure memory_hotplug.memmap_on_memory=Y, the following steps can be taken: Rescue from OOM situations: configure with memmap-on-memory enabled, online it. Thank you, Sumanth