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Wed, 19 Apr 2023 11:50:58 -0700 (PDT) Received: from localhost ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.gmail.com with ESMTPSA id z21-20020a7bc7d5000000b003f17848673fsm2974811wmk.27.2023.04.19.11.50.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Apr 2023 11:50:58 -0700 (PDT) Date: Wed, 19 Apr 2023 19:50:57 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Matthew Wilcox , David Hildenbrand , Pavel Begunkov , io-uring@vger.kernel.org Subject: Re: [PATCH v4 4/6] io_uring: rsrc: avoid use of vmas parameter in pin_user_pages() Message-ID: <0a41fd0e-39ce-48a4-b47b-53cf4cbb050b@lucifer.local> References: <956f4fc2204f23e4c00e9602ded80cb4e7b5df9b.1681831798.git.lstoakes@gmail.com> <936e8f52-00be-6721-cb3e-42338f2ecc2f@kernel.dk> <69f48cc6-8fc6-0c49-5a79-6c7d248e4ad5@kernel.dk> <8af483d2-0d3d-5ece-fb1d-a3654411752b@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: AFD6318002C X-Rspamd-Server: rspam01 X-Stat-Signature: 9ajpw7tiida838z8srkt8cwqzp895o7n X-HE-Tag: 1681930260-842954 X-HE-Meta: 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 N/oP1Iym 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 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: On Wed, Apr 19, 2023 at 03:22:19PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 19, 2023 at 07:18:26PM +0100, Lorenzo Stoakes wrote: > > > I'd also argue that we are doing things right with this patch series as-is, > > io_uring is the only sticking point because, believe it or not, it is the > > only place in the kernel that uses multiple vmas (it has been interesting > > to get a view on GUP use as a whole here). > > I would say io_uring is the only place trying to open-code bug fixes > for MM problems :\ As Jens says, these sorts of temporary work arounds become > lingering problems that nobody wants to fix properly. > > > So even if I did the FOLL_ALLOW_BROKEN_FILE_MAPPING patch series first, I > > would still need to come along and delete a bunch of your code > > afterwards. And unfortunately Pavel's recent change which insists on not > > having different vm_file's across VMAs for the buffer would have to be > > reverted so I expect it might not be entirely without discussion. > > Yeah, that should just be reverted. > > > However, if you really do feel that you can't accept this change as-is, I > > can put this series on hold and look at FOLL_ALLOW_BROKEN_FILE_MAPPING and > > we can return to this afterwards. > > It is probably not as bad as you think, I suspect only RDMA really > wants to set the flag. Maybe something in media too, maybe. > > Then again that stuff doesn't work so incredibly badly maybe there > really is no user of it and we should just block it completely. > > Jason OK in this case I think we're all agreed that it's best to do this first then revisit this series afterwards. I will switch to working on this! And I will make sure to cc- everyone in :)