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[2003:cb:c72a:da00:e63f:f575:6b1a:df4e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43656b4432dsm197359065e9.41.2024.12.24.03.32.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Dec 2024 03:32:21 -0800 (PST) Message-ID: <05d22a0e-013d-4c1e-bffa-820ad88983ef@redhat.com> Date: Tue, 24 Dec 2024 12:32:19 +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> <67fec986-6a5d-4b1e-a86f-7ecccb1bccf5@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-Queue-Id: 4E125C0009 X-Stat-Signature: 7rskg3mhszxspffn51aufgd77eapansj X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1735039905-538932 X-HE-Meta: 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 Gf7UMWHc p9pme6lHUVhU0ql8lPCXll4Jim9Daz/tgtVZNuwK6GgoolBhDQIKThUzry0DSQdkB0c6Sdt+DYdT4O3kxPigwMJeOPouzvSKNy4Mj971trNlc4gHaMCrku3h9CpDrbLJopFhMiHv7MEhVAi5Ju4mh5ziahkiD22+yx7UnhM/pIOwBkKJNjS+VFOf80rzi+k9xEbH5tqMwHNInJ2AZb2dhrknq2tcURVXTrnKXEsgx+cIJWX3muy/IcuS+n0hY/xGLtcF1zMIl9lux8D0E4gn80R6cN3muCNKMg4NXwJNJWUbfCSoRwhNkGmlbQnCyXqbnnKHKbln8pSMwFRGqmWnELItmamzSQ3eDCQS0mp0JcBZ3Hc2mSC7qeEgcGmMCXlk50HfcM0KyG988x+kurTBCAAzA22lEIgIwjbhR+Ub0zypIwDah5eBVJuN97yrQFekYRzqt X-Bogosity: Ham, tests=bogofilter, spamicity=0.003068, 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 22.12.24 03:47, Jingbo Xu wrote: > > > On 12/22/24 12:23 AM, David Hildenbrand wrote: >> 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. >> > > But that (memory compaction on memory allocation, which can be triggered > in the fuse server process context) only triggers MIGRATE_SYNC_LIGHT, > which won't wait for writeback. > Ah, that makes sense. > AFAICS, MIGRATE_SYNC can be triggered during cma allocation, memory > offline, or node compaction manually through sysctl. Right, non-proactive compaction always uses MIGRATE_SYNC_LIGHT, that won't wait. -- Cheers, David / dhildenb