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[2003:cb:c708:9d00:edd9:835b:4bfb:2ce3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c8472d5sm3911850f8f.47.2024.12.20.03.44.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Dec 2024 03:44:25 -0800 (PST) Message-ID: <71d7ac34-a5e5-4e59-802b-33d8a4256040@redhat.com> Date: Fri, 20 Dec 2024 12:44:24 +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: Shakeel Butt , Joanne Koong Cc: Bernd Schubert , Zi Yan , miklos@szeredi.hu, 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: <43e13556-18a4-4250-b4fe-7ab736ceba7d@redhat.com> <968d3543-d8ac-4b5a-af8e-e6921311d5cf@redhat.com> <7b6b8143-d7a4-439f-ae35-a91055f9d62a@redhat.com> <2e13a67a-0bad-4795-9ac8-ee800b704cb6@fastmail.fm> <2bph7jx4hvhxpgp77shq2j7mo4xssobhqndw5v7hdvbn43jo2w@scqly5zby7bm> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: D7DDF140002 X-Stat-Signature: 31cz565j1hn3kynyuppg6ukkxkp96g6c X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1734695045-626696 X-HE-Meta: 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 L0VFeWpc iMi7A7Dze/4nkEP4kiU2jkYwNIwzo+/D9Ck1NVagiyMjNTPL+mkcErSE3mra/T2NvWOlm6D1gBnpeDkTKj2vc0n6csu74I1skdPPQkPZulyEebHsRAr7r9xtPm+CJdCveKEOmt/4lnZr3g2wr5rR7VGzJoi9S3LjgILzJh+gj5/vVXsaGCfZDQfwLhHXLhRK7ZpyHEmcMgs9Trd90jRAUDtZQDdrQhr8lAuzdeMTDPIDM+QFqjrWC6MunemSk6lTrzX3MfyG37i/USeaultxuejKXU0cBgtlcSv8JbRnBt8iTuS2/R/T7SkJwP5TRGhV40TQsH7kJc+F0QqekaiDYokKGyWk12ubZM+fhG5dy/cV9FJFpBB6hbiYD/gfIllXPGZse7JMqjHfjEroxaz8uA922vG+wlyyo2JqMHWXqDUXrzfKacoqyXzjnZtriDouzrw1WWm8t/B8l/SuN2YRwqj8pHg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.070642, 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 19.12.24 18:54, Shakeel Butt wrote: > On Thu, Dec 19, 2024 at 09:44:42AM -0800, Joanne Koong wrote: >> On Thu, Dec 19, 2024 at 9:37 AM Shakeel Butt wrote: > [...] >>>> >>>> The request is canceled then - that should clear the page/folio state >>>> >>>> >>>> I start to wonder if we should introduce really short fuse request >>>> timeouts and just repeat requests when things have cleared up. At least >>>> for write-back requests (in the sense that fuse-over-network might >>>> be slow or interrupted for some time). >>>> >>>> >>> >>> Thanks Bernd for the response. Can you tell a bit more about the request >>> timeouts? Basically does it impact/clear the page/folio state as well? >> >> Request timeouts can be set by admins system-wide to protect against >> malicious/buggy fuse servers that do not reply to requests by a >> certain amount of time. If the request times out, then the whole >> connection will be aborted, and pages/folios will be cleaned up >> accordingly. The corresponding patchset is here [1]. This helps >> mitigate the possibility of unprivileged buggy servers tieing up >> writeback state by not replying. >> > > Thanks a lot Joanne and Bernd. > > David, does these timeouts resolve your concerns? Thanks for that information. Yes and no. :) Bernd wrote: "I start to wonder if we should introduce really short fuse request timeouts and just repeat requests when things have cleared up. At least for write-back requests (in the sense that fuse-over-network might be slow or interrupted for some time). Indicating to me that while timeouts might be supported soon (will there be a sane default?) even trusted implementations can run into this (network example above) where timeouts might actually be harmful I suppose? 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. -- Cheers, David / dhildenb