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[2003:cb:c708:e100:4f41:ff29:a59f:8c7a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e37d012sm5360241f8f.8.2025.01.10.12.20.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jan 2025 12:20:09 -0800 (PST) Message-ID: Date: Fri, 10 Jan 2025 21:20:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Jeff Layton , Shakeel Butt , Miklos Szeredi Cc: Joanne Koong , Bernd Schubert , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko References: <0ed5241e-10af-43ee-baaf-87a5b4dc9694@redhat.com> <446704ab-434e-45ac-a062-45fef78815e4@redhat.com> <791d4056-cac1-4477-a8e3-3a2392ed34db@redhat.com> <153c5a4f08daf60e1bbbdde02975392dc608cfdf.camel@kernel.org> From: David Hildenbrand 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: <153c5a4f08daf60e1bbbdde02975392dc608cfdf.camel@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: iX8cNcVve1mzYID-wtzE8MjC5dq5oPKILuUWwosNsFM_1736540411 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: rspam10 X-Rspamd-Queue-Id: 5B8AEC0008 X-Stat-Signature: 5zdm3hcesr3bjwy15on6npaqxtyxnckz X-Rspam-User: X-HE-Tag: 1736540416-424652 X-HE-Meta: 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 rAdxyyCn SInvSin4kESp8UQsH5XHxXttSIfTig/zI/p9dvQS6jVDdbxAGi15XuFXwy3vbcKC5erD0PVytGl8EBd2vIdep/yFIpY1kTbDwvH1DL7ZHBkyfejDX0uCjv3TT0MDPPEgRm/O+46NgtYYjb6cBONgyVoOiUK8MNA3HyGcEvsY77eda2aoZ2lWMLnUSt6aHAJ9WLpXwgbVirZGUs/y9KH7pN+L0c/5I0YE6ePIkEzOCdt6e538uPfUAzssWbwadg8KgTeIVZ6cf4KbufrxVF7HA8QQjRjuuj1ykRF+09lJcQbeL8AlvfMMqc8eFsRKBknjFyPtLiQ7BnNXcPWghwHCgvzs98TOTl8WgJ/MTbGF2N1AxvQJt1AfHoB9facw3yH0jikCsqNrIo/KSan0u8hKLT8WK7iI/fb2muPqxzkY8Sdl9PxfYkVDduxnOljM9GOFfTVY7gZV+x4p17rHN9gEtqnY6LA== 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 10.01.25 21:16, Jeff Layton wrote: > On Tue, 2025-01-07 at 09:34 +0100, David Hildenbrand wrote: >> On 06.01.25 19:17, Shakeel Butt wrote: >>> On Mon, Jan 06, 2025 at 11:19:42AM +0100, Miklos Szeredi wrote: >>>> On Fri, 3 Jan 2025 at 21:31, David Hildenbrand wrote: >>>>> In any case, having movable pages be turned unmovable due to persistent >>>>> writaback is something that must be fixed, not worked around. Likely a >>>>> good topic for LSF/MM. >>>> >>>> Yes, this seems a good cross fs-mm topic. >>>> >>>> So the issue discussed here is that movable pages used for fuse >>>> page-cache cause a problems when memory needs to be compacted. The >>>> problem is either that >>>> >>>> - the page is skipped, leaving the physical memory block unmovable >>>> >>>> - the compaction is blocked for an unbounded time >>>> >>>> While the new AS_WRITEBACK_INDETERMINATE could potentially make things >>>> worse, the same thing happens on readahead, since the new page can be >>>> locked for an indeterminate amount of time, which can also block >>>> compaction, right? >> >> Yes, as memory hotplug + virtio-mem maintainer my bigger concern is >> these pages residing in ZONE_MOVABLE / MIGRATE_CMA areas where there >> *must not be unmovable pages ever*. Not triggered by an untrusted >> source, not triggered by an trusted source. >> >> It's a violation of core-mm principles. >> >> Even if we have a timeout of 60s, making things like alloc_contig_page() >> wait for that long on writeback is broken and needs to be fixed. >> >> And the fix is not to skip these pages, that's a workaround. >> >> I'm hoping I can find an easy way to trigger this also with NFS. >> > > I imagine that you can just open a file and start writing to it, pull > the plug on the NFS server, and then issue a fsync or something to > ensure some writeback occurs. Yes, that's the plan, thanks! > > Any dirty pagecache folios should be stuck in writeback at that point. > The NFS client is also very patient about waiting for the server to > come back, so it should stay that way indefinitely. Yes, however the default timeout for UDP is fairly small (for TCP certainly much longer). So one thing I'd like to understand what that "cancel writeback -> redirty folio" on timeout does, and when it actually triggers with TCP vs UDP timeouts. -- Cheers, David / dhildenb