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[2003:cb:c70e:d000:4622:73e7:6184:8f0d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c828e3fsm6928799f8f.5.2024.12.21.08.23.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 21 Dec 2024 08:23:12 -0800 (PST) Message-ID: <67fec986-6a5d-4b1e-a86f-7ecccb1bccf5@redhat.com> Date: Sat, 21 Dec 2024 17:23:10 +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: Jingbo Xu , Shakeel Butt Cc: Bernd Schubert , Joanne Koong , Zi Yan , miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko References: <968d3543-d8ac-4b5a-af8e-e6921311d5cf@redhat.com> <7b6b8143-d7a4-439f-ae35-a91055f9d62a@redhat.com> <2e13a67a-0bad-4795-9ac8-ee800b704cb6@fastmail.fm> <2bph7jx4hvhxpgp77shq2j7mo4xssobhqndw5v7hdvbn43jo2w@scqly5zby7bm> <71d7ac34-a5e5-4e59-802b-33d8a4256040@redhat.com> <9404aaa2-4fc2-4b8b-8f95-5604c54c162a@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-Server: rspam04 X-Rspamd-Queue-Id: BB11580006 X-Stat-Signature: 3zcfw486h7tw3st4bdpkryt99swenctt X-Rspam-User: X-HE-Tag: 1734798128-733432 X-HE-Meta: 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 l3SRocC9 I0bOAbzmh8IeBkh5JKeVIgORoNiN74Y77/IyD0aPoP9zeASL+pmikQRHAwXgUPca1TklfRNy/qH5MLJlr4YhyrJ0Kh94NjtAoWKIII8HB6OWAMSUKVVTdv2CAxqEFk4wEPy1IngF2kTGhjrh039Neps76Qll5nN4i+yYeSd0FDvhoyWG4tyDQGhnQkc8FNvTMsZw+eyB5c40L4HN8RY6ocebdoiX/6GVSWQLuTH2wfJwNJh0KHDHkT6lR4PlmV7kwp0R/s/joyrk1OjrGu/Uz3ZMYxuLBwbZtj0nX0Y9EtFDfZ/7NRKXbEX2VHYMXxy9nNZ6XTU5KaDqb1Vp/nGzoWywhgK0HrBHBGEtgR4zE05eTCnMGP0kuHYUP0k9kW7S/5OdIIdCgX/RjiSbolJkbbaDTj9zULKe8TR3Ft7xsCu0c90ARcJ8B8fOWi9+hQURvTZJZ X-Bogosity: Ham, tests=bogofilter, spamicity=0.302778, 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 21.12.24 03:28, Jingbo Xu wrote: > > > On 12/21/24 2:01 AM, Shakeel Butt wrote: >> On Fri, Dec 20, 2024 at 03:49:39PM +0100, David Hildenbrand wrote: >>>>> I'm wondering if there would be a way to just "cancel" the writeback and >>>>> mark the folio dirty again. That way it could be migrated, but not >>>>> reclaimed. At least we could avoid the whole AS_WRITEBACK_INDETERMINATE >>>>> thing. >>>>> >>>> >>>> That is what I basically meant with short timeouts. Obviously it is not >>>> that simple to cancel the request and to retry - it would add in quite >>>> some complexity, if all the issues that arise can be solved at all. >>> >>> At least it would keep that out of core-mm. >>> >>> AS_WRITEBACK_INDETERMINATE really has weird smell to it ... we should try to >>> improve such scenarios, not acknowledge and integrate them, then work around >>> using timeouts that must be manually configured, and ca likely no be default >>> enabled because it could hurt reasonable use cases :( >> >> Just to be clear AS_WRITEBACK_INDETERMINATE is being used in two core-mm >> parts. First is reclaim and second is compaction/migration. For reclaim, >> it is a must have as explained by Jingbo in [1] i.e. due to potential >> self deadlock by fuse server. If I understand you correctly, the main >> concern you have is its usage in the second case. >> >> The reason for adding AS_WRITEBACK_INDETERMINATE in the second case was >> to avoid untrusted fuse server causing pain to unrelated jobs on the >> machine (fuse folks please correct me if I am wrong here). > > Right, IIUC direct MIGRATE_SYNC migration won't be triggered on the > memory allocation path, i.e. the fuse server itself won't stumble into > MIGRATE_SYNC migration. > Maybe memory compaction (on higher-order allocations only) could trigger it? gfp_compaction_allowed() checks __GFP_IO. GFP_KERNEL includes that. -- Cheers, David / dhildenb