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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1ppCSK-00DTvc-RX; Wed, 19 Apr 2023 18:23:00 +0000 Date: Wed, 19 Apr 2023 19:23:00 +0100 From: Matthew Wilcox To: Lorenzo Stoakes Cc: Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Pavel Begunkov , io-uring@vger.kernel.org, Jason Gunthorpe Subject: Re: [PATCH v4 4/6] io_uring: rsrc: avoid use of vmas parameter in pin_user_pages() Message-ID: 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-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B6A97120007 X-Rspam-User: X-Stat-Signature: za9gocwx9r3xzzgpoy4myhu1ip9ar9y6 X-HE-Tag: 1681928583-434876 X-HE-Meta: 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 /2/DT8oR BgTe1y5XnzjmkiidLFObMAVmRYUG/oiZAKGSCD5EcD//PYV4/HybmE+kFznd1kPqqK2gOSVBiiEbEEBVVsh45e37XxO5fZGK4Xxor9kz6SpzlQ/6JLjf2L8V2XmbSM+UqsNeBU6LYAUBqNyKZzmb+SDUWPseXk0W9aBQYUpAy4edNcga8pCmg8V3dXRWoa2YP47L5yCg2C6bACGE+m4q7xHMCqGkLUPccgCfHEROeRcrYrgMlFg24YDFpFFbFYqs+dqxdLIeLgTPdl7XsbUPK7Mz3oLcHRGSnFKcmWtnset++jO4tryDnqXXd1Nccp/cPqY7993dotyjUwDhKNnT2sc1guEMu6wZlK/Cx 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 07:18:26PM +0100, Lorenzo Stoakes wrote: > 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. I don't even understand why Pavel wanted to make this change. The commit log really doesn't say. commit edd478269640 Author: Pavel Begunkov Date: Wed Feb 22 14:36:48 2023 +0000 io_uring/rsrc: disallow multi-source reg buffers If two or more mappings go back to back to each other they can be passed into io_uring to be registered as a single registered buffer. That would even work if mappings came from different sources, e.g. it's possible to mix in this way anon pages and pages from shmem or hugetlb. That is not a problem but it'd rather be less prone if we forbid such mixing. Cc: Signed-off-by: Pavel Begunkov Signed-off-by: Jens Axboe It even says "That is not a problem"! So why was this patch merged if it's not fixing a problem? It's now standing in the way of an actual cleanup. So why don't we revert it? There must be more to it than this ...