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Wed, 12 Jul 2023 03:16:57 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4916020049; Wed, 12 Jul 2023 03:16:57 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9934620040; Wed, 12 Jul 2023 03:16:54 +0000 (GMT) Received: from [9.43.19.28] (unknown [9.43.19.28]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Jul 2023 03:16:54 +0000 (GMT) Message-ID: Date: Wed, 12 Jul 2023 08:46:53 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation Content-Language: en-US To: David Hildenbrand , linux-mm@kvack.org, akpm@linux-foundation.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, christophe.leroy@csgroup.eu References: <20230711044834.72809-1-aneesh.kumar@linux.ibm.com> <20230711044834.72809-5-aneesh.kumar@linux.ibm.com> From: Aneesh Kumar K V In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: PlV2REpOD43DliAbdNhE8ampXrKu_A3q X-Proofpoint-GUID: UyW1V1lCTRxaFCT6siDIkjXKWpktBoJe X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-07-11_14,2023-07-11_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxlogscore=769 clxscore=1015 suspectscore=0 impostorscore=0 mlxscore=0 phishscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2307120025 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: , Cc: Vishal Verma , Michal Hocko , Oscar Salvador Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 7/11/23 10:49 PM, David Hildenbrand wrote: > On 11.07.23 06:48, Aneesh Kumar K.V wrote: >> Add a new kconfig option that can be selected if we want to allow >> pageblock alignment by reserving pages in the vmemmap altmap area. >> This implies we will be reserving some pages for every memoryblock >> This also allows the memmap on memory feature to be widely useful >> with different memory block size values. > > "reserving pages" is a nice way of saying "wasting memory". :) Let's spell that out. > > I think we have to find a better name for this, and I think we should have a toggle similar to memory_hotplug.memmap_on_memory. This should be an admin decision, not some kernel config option. > > > memory_hotplug.force_memmap_on_memory > > "Enable the memmap on memory feature even if it could result in memory waste due to memmap size limitations. For example, if the memmap for a memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB > of hotplugged memory will be wasted. Note that there are still cases where the feature cannot be enforced: for example, if the memmap is smaller than a single page, or if the architecture does not support the forced mode in all configurations." > > Thoughts? > With module parameter, do we still need the Kconfig option? -aneesh