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Sat, 21 Dec 2024 10:28:58 +0800 Message-ID: Date: Sat, 21 Dec 2024 10:28:57 +0800 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 , David Hildenbrand 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> Content-Language: en-US From: Jingbo Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 7E7D840008 X-Stat-Signature: juspop14m6dg7q1ohfoq6rfe7f7cona8 X-Rspam-User: X-HE-Tag: 1734748088-244101 X-HE-Meta: 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 HiZXRFSc L2VkHuP/FVD8BzqK85Q5rmSPjC8X7Ac6ZS9ydRl0NHSzlcwmeWG3e5i0yLlJNESXRcH3lRYpelm3D6K6Hb31gdhpCU5rHitZUVSfcKaXM9FpVfLkIBcXqFD6LMkI77OdYpCUK7nQEWBq+SEirhPGszmw0QTWh4hOQKUIyV81QrJoddf0tpLLBDtgqiLUMUD/SWbkGQt5a8Per+O3fzYYy8HO0DnT8FANoL07TuHTfj2sgiPYQiAGzXHYpxcCCV5mnWkiqnc4x/TZH6N3LNpt7NrB6j3LZpzRBzIUniC57VZYOz0w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000006, 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 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. -- Thanks, Jingbo