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[2003:cb:c739:900:900f:3c9e:2f7b:5d0a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d8dd6sm13231254f8f.62.2025.02.17.11.52.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Feb 2025 11:52:34 -0800 (PST) Message-ID: Date: Mon, 17 Feb 2025 20:52:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 1/3] mm/filemap: add mempolicy support to the filemap layer To: Shivank Garg , akpm@linux-foundation.org, willy@infradead.org, pbonzini@redhat.com Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, chao.gao@intel.com, seanjc@google.com, ackerleytng@google.com, vbabka@suse.cz, bharata@amd.com, nikunj@amd.com, michael.day@amd.com, Neeraj.Upadhyay@amd.com, thomas.lendacky@amd.com, michael.roth@amd.com, Shivansh Dhiman , baolin.wang@linux.alibaba.com References: <20250210063227.41125-1-shivankg@amd.com> <20250210063227.41125-2-shivankg@amd.com> <76537454-272b-4fbb-b073-5387bbaaf28d@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 2931F1C0006 X-Stat-Signature: rh7uygtxo3yjw65qsax79mibcqk3eryk X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1739821959-924008 X-HE-Meta: U2FsdGVkX1+lc9j0lv3dg7At9cxIEb4NrJASssNwbPlc38bvQVEwLhQSS8igomQNm3yWPU1/kAgvh5U5sApdQxhctxdieNUGfZqyyaK7WpajiCjEwx8QitP4kiXlpcr0VNVtecgq97xiQWHElAnMBD1Yth4eHjNtwzEWJc6m5gWHLHhxPcYDASfMVzi4KXAveFQ+/r2zc1/8+X/ARzh12YItXNvH4tJ5+h+PcImEkPUy7ssLrRQ4uvbM2avqxB/nWmRya6ksEeADalb7afTrYW0VzaOOhtw+RI/EKInX2o3PxstmicwmL+FzRtkuIeF+Bxkz8goHwge2DuOPSK7+Udl1jF4Lz9AS9l51Sb7/N63dhmD7KhTsoNXo/OoLqEyk+8GkJtQ7wpNMA8QONxMvcwicSHs5C3KIOySn3acV8QFzvjmqRA0WXGPtOOmlU2wdKOB2oI0a3BgIclZSei78vZ1hbwKsuCi4ncnejnqr1SOnoqVTjSHVZcLd4Ti2qf1/ZI1QafI9hf1uwJT8hm6vLLVqF1Xl/wlvk0BU8Uo6NZqyqfrce/E3mgb0o0MY0I1bIpZXl6xD5f2c010lZhTo0xadEwzUlmfP8cuxf5oIbiZmdCvLGlAnaSXBUqHIwWi+hebo5/ot68U8scui5x9tWuoxiiDiZvUKa052hu/Gr9KWqLbamfSfeH89FjTif7TzCaNWOt8RA2/dnGhCUyXIpDF4HqPzR+C3epfTCJZFZDIzbBE4UdgPJ3Rg9pq6y6QWG+/VKmpqfvK9aBU9b68ajx1GP3SYln9opK9t5q8tUDv4OWzbA+if4EHDBinLCKGe7bc9MzCqJXaHSrDNXBJFBhV1tLmzFtc55g8bOpNn7cOpPLWEJe1XF9zLijcj6+tY8dO9zgntNezJ6Fsp+M2j8Ury6/GCK+bIOYUEiM+51ZefN7bYywnOun9CMfWK+Dj947+qX21niBCAr2BK1bg kg+88gHi TKDsPgKDy4BCXtmxZFrVU6sI58MtQe7OXBTmongguDQD7Kj9s1P8U8SWIxQjGUOTVdsZIs/7hmdMjHo98ptf0Nk+H/d3OHg8iCsTY2BHKACYFwFKDI9nuXefna2oUPLpDAii8nRBDUHyPWBNvuEPYPUQmMHHTScUOW/1HNlTJhrOs3GligfBfZH24Ht+L00fy6zA6LBhNPXwdjnsiiy5rL/Ur91NuvgkDRX7+JYYlr8iGsGVTLiCXFKQQTMKCaIHTC8qAYbOn/wf8WVpshOw2VdJXsiNx1kL9C9An7rWW5C2NK9SAm+HuX+V0BUur+83CSQ0cnSCsqDgbuD5SZ7oPcxir0CFSVkDcaI7+4FGs/qp9a3nv+AfwvrCymoHb4GmPkre5K/OK+dp+OOg= 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: > > (1) As you noted later, shmem has unique requirements due to handling swapin. > It does considerable open-coding. > Initially, I was considering simplifying the shmem but it was not possible due > to above constraints. > One option would be to add shmem's special cases in the filemap and check for > themusing shmem_mapping()? > But, I don't understand the shmem internals well enough to determine if it is > feasible. > Okay, thanks for looking into this. > (2) I considered handling it manually in guest_memfd like shmem does, but this > would lead to code duplication and more open-coding in guest_memfd. The current > approach seems cleaner. Okay, thanks. > >> Two tabs indent on second parameter line, please. >> > .. >> >> This should go below the variable declaration. (and indentation on second parameter line should align with the first parameter) >> > .. >> "The mempolicy to apply when allocating a new folio." ? >> > > I'll address all the formatting and documentation issues in next posting. > >> >> For guest_memfd, where pages are un-movable and un-swappable, the memory policy will never change later. >> >> shmem seems to handle the swap-in case, because it keeps care of allocating pages in that case itself. >> >> For ordinary pagecache pages (movable), page migration would likely not be aware of the specified mpol; I assume the same applies to shmem? >> >> alloc_migration_target() seems to prefer the current nid (nid = folio_nid(src)), but apart from that, does not lookup any mempolicy. > > Page migration does handle the NUMA mempolicy using mtc (struct migration_target_control *) > which takes node ID input and allocates on the "preferred" node id. > The target node in migrate_misplaced_folio() is obtained using get_vma_policy(), so the > per-VMA policy handles proper node placement for mapped pages. > It use current nid (folio_nid(src)) only if NUMA_NO_NODE is passed. > > mempolicy.c provides the alloc_migration_target_by_mpol() that allocates according to > NUMA mempolicy, which is used by do_mbind(). > >> >> compaction likely handles this by comapcting within a node/zone. >> >> Maybe migration to the right target node on misplacement is handled on a higher level lagter (numa hinting faults -> migrate_misplaced_folio). Likely at least for anon memory, not sure about unmapped shmem. > > Yes. Thanks, LGTM. -- Cheers, David / dhildenb