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b=ITH1SfL9/zU15o1E1iAQjeukJh5FkXRn/rUOWQjgchYsoLnfG6CQNPDmkYQWSIGtA flAwOMq4gnrxIY64c1aNj8iKGJWTtQFzfGweGo/onTzL4vpk5oXeSIk20LEnpPeXXt C0pgo890yABHW1jPPR2yX6XQCccneiRP7V/XG0EeUKjwRC4CoYZ8IVoU3JjrxnmAod HiKByqpkXFRyyMnC0Aj6gbr5ueeiX7S1Mn1WM9uWmV68ehvqF9pQyzHRkBqr1c1o1c 00hWesaUNkTugeyf+fQ4AKFEOnvmyGMVT7rElu2qfPAqenL8AcjySokDq53iH5vJCf /TA5xQp4963ww== Message-ID: <90418cd3-751f-439d-83ed-a0c33517c3bd@kernel.org> Date: Thu, 18 Jun 2026 10:21:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC][RFC PATCH v4 00/27] Private Memory Nodes (w/ Compressed RAM) Content-Language: en-US To: Gregory Price , "David Hildenbrand (Arm)" Cc: Balbir Singh , lsf-pc@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, damon@lists.linux.dev, kernel-team@meta.com, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com, longman@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, osalvador@suse.de, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, yury.norov@gmail.com, linux@rasmusvillemoes.dk, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, jackmanb@google.com, sj@kernel.org, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, muchun.song@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, jannh@google.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, pfalcato@suse.de, rientjes@google.com, shakeel.butt@linux.dev, riel@surriel.com, harry.yoo@oracle.com, cl@gentwo.org, roman.gushchin@linux.dev, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, zhengqi.arch@bytedance.com, terry.bowman@amd.com, Matthew Wilcox References: <9f1815b0-896b-44ab-9e6d-9316d8f11033@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8860718000A X-Stat-Signature: wsg3kocjuwjecxzfrhgzt9o56hokygf7 X-HE-Tag: 1781770906-801390 X-HE-Meta: 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 xfOm+6NN ScFjU/YQa9jG57xDLfhEF51sQvsHhhuvvO2muYFFJ7ZWPcRXoB3/d7S6/7wnM8sQoHS4jPdvY0pQ6qG/sJxWGHr1LiiXecpe2xE+hHZkQnLSbzavxrdYcjOM2cDCK3TMm8nwsLEBoaXiVKTj7CRB3jyHGK/cwx6m0aUwvQ26kjswMM1duQ54VA5PHXW58TYCChKzP+KLHLtsw+8EuJq0vp9WAOoDkNZhlsp1J2wBxAZaptsX+ekHvoI2e2ioRKUxCT8VPDI2RPmNP4VzhoDUHVzQspjvXnGSasYcJIA0kddqzZ3MbrfP3nj79QkqMPrCRoEfAdo5AtYLcydE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/15/26 17:37, Gregory Price wrote: > On Mon, Jun 15, 2026 at 05:18:55PM +0200, David Hildenbrand (Arm) wrote: >> On 6/15/26 16:38, Vlastimil Babka (SUSE) wrote: >> > >> > I think the memalloc approach is dangerous due to unexpected nesting. There >> > might be nested page allocations in page allocation itself (due to some >> > debugging option). But also interrupts do not change what "current" points >> > to. Suddenly those could start requesting folios and/or private nodes and be >> > surprised, I'm afraid. >> >> Yeah, we'd need some way to distinguish the main allocation from these other >> (nested) allocations. >> >> >> > >> > The memalloc scopes only work well when they restrict the context wrt >> > reclaim, and allocations in IRQ have to be already restricted heavily >> > (atomic) so further memalloc restrictions don't do anything in practice. But >> > to make them change other aspects of the allocations like this won't work. >> >> I was assuming that memalloc_pin_save() would already violate that, but really >> it only restricts where movable allocations land, and that doesn't matter for >> other kernel allocations. >> >> Do you see any other way to make something like an allocation context work, and >> avoid introducing more GFP flags? >> > > One thought would be a way to switch what fallback list is used, and > then have specific fallback lists for certain contexts. > > Right now there is a single example of this: __GFP_THISNODE > |= __GFP_THISNODE => NOFALLBACK > &= ~__GFP_THISNODE => FALLBACK > > We could add an interface with the desired fallback list based as an > argument, and let get_page_from_freelist to prefer that over the default > global lists. Does it mean a new argument in a number of functions in the page allocator, or can it be mapped to alloc_flags (at least internally?), because the number of possible fallback lists is small enough? > Omit all special nodes from FALLBACK/NOFALLBACK and make the special > contexts provide the fallback-base that should be used. > > On my current branch i think that would include modifying, in totality: > > alloc_folio_mpol() > alloc_demotion_folio() > alloc_migration_target() > > And i'm pretty sure that all just nests nicely. > > We might not even need memalloc... hmmm > > ~Gregory