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Wed, 21 May 2025 14:21:51 +0000 (GMT) Date: Wed, 21 May 2025 16:21:49 +0200 From: Heiko Carstens To: David Hildenbrand Cc: Sumanth Korikkar , linux-mm , Andrew Morton , Oscar Salvador , Gerald Schaefer , Vasily Gorbik , Alexander Gordeev , linux-s390 , LKML Subject: Re: [RFC PATCH 1/4] mm/memory_hotplug: Add interface for runtime (de)configuration of memory Message-ID: <20250521142149.11483C95-hca@linux.ibm.com> References: <20241202082732.3959803-1-sumanthk@linux.ibm.com> <20241202082732.3959803-2-sumanthk@linux.ibm.com> <3151b9a0-3e96-4820-b6af-9f9ec4996ee1@redhat.com> <1b9285ba-4118-4572-9392-42ec6ba6728c@redhat.com> <496e6707-bdc9-4ad2-88e2-51236549b5f2@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <496e6707-bdc9-4ad2-88e2-51236549b5f2@redhat.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTIxMDEzNyBTYWx0ZWRfX+es2tdgCqTRk DJ+MBFcXGJjGaWxKeOwxOXX3HaifE2jsF6o6EwdTUz637IAAyyIRmyLieBEilYuL54IzOfj0uKG 8HHZ05z1Lql7XFezD4n0z5MK24sCeu3zexFnWdV1fJwa6WuHsVUolLZibcVmeHFKhcknn9qtLkd +kaIFrHEc3EIIymkdgsHfPT4OzYAuhh8oZOZ1jUO5628XXKDKI4nh0bsHAz2yEk2qqAjfNgvG+m Cw1MKRlRUONC51E+plTgUo7+a6cbh3VwUCjX0y4oF9p7caNfRkw5uoMW5fWQN2cWjo2R8Wa1m1a +bOe8AKjG39CDxcnSp7JJ+InPS70cPMvcfE6kJ+HgJrpOYlozVzL7EkbH0Gml0uthDWVH5qziRt 8q6zrAwx7FEjXojfog8xb5rI6LNv5FstR6KVYmRF0dFL6jq/wj8OYGvrRPKXXwchRIxRoaI3 X-Authority-Analysis: v=2.4 cv=esrfzppX c=1 sm=1 tr=0 ts=682de184 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=dt9VzEwgFbYA:10 a=nzSEty_UkPgyXC6r39YA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-ORIG-GUID: x4PT5vUB9_qT4dlNxpPKkjz48cYLT3z2 X-Proofpoint-GUID: x4PT5vUB9_qT4dlNxpPKkjz48cYLT3z2 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-21_04,2025-05-20_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 malwarescore=0 lowpriorityscore=0 impostorscore=0 suspectscore=0 spamscore=0 phishscore=0 priorityscore=1501 clxscore=1011 bulkscore=0 mlxscore=0 mlxlogscore=346 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505160000 definitions=main-2505210137 X-Stat-Signature: 4d7eucmker14x65e5uwjrdndg17pee5u X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B099C4000F X-HE-Tag: 1747837317-177617 X-HE-Meta: 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 r82EsBlB vXBS+2uLSS4Ahvq75QX4kMghPsmA2b7WN3KdIALfwgJ5eF2nRupcQ9kTxBEJxBiynUfZmDIhWIGhHOaS4kq+Ct4O1IXIM4ZE26x+IGHGzH/1iZzyi3A+QepQih8M2tkm5OaCVbESPIL01igTgZCF7WEosw7GKS6JhmFRfvTtWBNoJGuhCq34XzCshK5+ZT+USrKW4y3NSp/XxPeIbeqEnTK6zCe9+ItwFrYYY+I1zKeD/By7XD8fnmQwnsHHaScRoAixZAoasPbZ3xNaeNchsx2AXJWkPdw9RL9yPqV5vlZmR+jFeoh01nsYpFoMSGXphNRVXX/S4w2iyoloDb+q5G5opjvMe1I855tmJJcO9c0NExS+4YH/wmLj5mIKyXE3fe8dHeVnLJDlgaFI= 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: On Wed, May 21, 2025 at 02:33:42PM +0200, David Hildenbrand wrote: > On 21.05.25 12:34, Sumanth Korikkar wrote: > > As you pointed out, how about having something similar to > > 73954d379efd ("dax: add a sysfs knob to control memmap_on_memory behavior") > > Right. But here, the use case is usually (a) to add a gigantic amount of > memory using add_memory(), not small blocks like on s390x (b) consume the > memmap from (slow) special-purpose memory as well. > > Regarding (a), the memmap could be so big that add_memory() might never > really work (not just because of some temporary low-memory situation). What is "big"? Worst case for s390 with existing machines would be an increment size (aka memory block size) of 64GB. So more than 1GB for memmap plus pages tables, etc would be required.