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Mon, 24 Mar 2025 11:55:55 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHKT0AIGOD74uSCO7EpMRdLffUkeO90SPxsewBmpglboi/Ese+zvtNAM2TxfbNzdmxW7TizeQ== X-Received: by 2002:a05:6214:2027:b0:6e6:9b86:85d0 with SMTP id 6a1803df08f44-6eb3493113bmr263136076d6.8.1742842555398; Mon, 24 Mar 2025 11:55:55 -0700 (PDT) Received: from [172.22.33.10] ([99.209.85.25]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6eb3efda6f2sm47138366d6.116.2025.03.24.11.55.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Mar 2025 11:55:55 -0700 (PDT) Message-ID: Date: Mon, 24 Mar 2025 19:55:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Migrating the un-migratable From: David Hildenbrand To: "lsf-pc@lists.linux-foundation.org" Cc: linux-fsdevel@vger.kernel.org, "linux-mm@kvack.org" , Jeff Layton , Zi Yan , Shakeel Butt , Joanne Koong , Miklos Szeredi References: <882b566c-34d6-4e68-9447-6c74a0693f18@redhat.com> Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <882b566c-34d6-4e68-9447-6c74a0693f18@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: E5ZAOVqsQgTODUV2aokt87nSixHi9wMzVfUuEdNCpig_1742842556 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7880BC0007 X-Stat-Signature: 4hwdxju8ag9gugohqh8sktyhscnukmym X-Rspam-User: X-HE-Tag: 1742842558-610050 X-HE-Meta: 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 PO7YJ6gA 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, 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 29.01.25 17:10, David Hildenbrand wrote: > Hi, > > ___GFP_MOVABLE allocations are supposed to be movable -> migratable: the > page allocator can place them on > MIGRATE_CMA/ZONE_MOVABLE/MIGRATE_MOVABLE areas: areas where the > expectation is that allocations can be migrated (somewhat reliably) to > different memory areas on demand. > > Mechanisms that turn such allocations unmigratable, such as long-term > page pinning (FOLL_LONGTERM), migrate these allocations at least out of > MIGRATE_CMA/ZONE_MOVABLE areas first. > > Ideally, we'd only perform this migration if really required (e.g., > long-term pinning), and rather "fix" other cases to not turn allocations > unmigratable. > > However, we have some rather obscure cases that can turn migratable > allocations effectively unmigratable for a long/indeterminate time, > possibly controlled by unprivileged user space. > > Possible effects include: > * CMA allocations failing > * Memory hotunplug not making progress > * Memory compaction not working as expected > > Some cases I can fix myself [1], others are harder to tackle. > > As one example, in context of FUSE we recently discovered that folios > that are under writeback cannot be migrated, and user space in control > of when writeback will end. Something similar can happen ->readahead() > where user space is in charge of supplying page content. Networking > filesystems in general seem to be prone to this as well. > > As another example, failing to split large folios can prevent migration > if memory is fragmented. XFS (IOMAP in general) refuses to split folios > that are dirty [3]. Splitting of folios and page migration have a lot in > common. > > This session is to collect cases that are known to be problematic, and > to start discussing possible approaches to make some of these > un-migratable allocations migratable, or alternative strategies to deal > with this. > > > [1] https://lkml.kernel.org/r/20250129115411.2077152-1-david@redhat.com > [2] > https://lkml.kernel.org/r/CAJnrk1ZCgff6ZWmqKzBXFq5uAEbms46OexA1axWS5v-PCZFqJg@mail.gmail.com > [3] > https://lkml.kernel.org/r/4febc035-a4ff-4afe-a9a0-d127826852a9@redhat.com > Slides from today: https://drive.google.com/file/d/1uX80M1x86Oz3DFoHif-JLx1rlC_Nh93R/view?usp=sharing -- Cheers, David / dhildenb