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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id m6-20020adfdc46000000b002d45575643esm2047200wrj.43.2023.04.20.06.57.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Apr 2023 06:57:58 -0700 (PDT) Date: Thu, 20 Apr 2023 14:57:57 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , 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: <5ead8d8c-6f47-4db1-b1da-ffaaee4be255@lucifer.local> References: <69f48cc6-8fc6-0c49-5a79-6c7d248e4ad5@kernel.dk> <8af483d2-0d3d-5ece-fb1d-a3654411752b@kernel.dk> <8bf0df41-27ef-4305-b424-e43045a6d68d@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: k3oygepmwz4e6f675sdj7bbrxw8i9dy1 X-Rspam-User: X-Rspamd-Queue-Id: 01B86C000C X-Rspamd-Server: rspam06 X-HE-Tag: 1681999080-607039 X-HE-Meta: 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 9l6EilwP 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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 08:22:51PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 19, 2023 at 07:45:06PM +0100, Lorenzo Stoakes wrote: > > > For example, imagine if a user (yes it'd be weird) mlock'd some pages in a > > buffer and not others, then we'd break their use case. Also (perhaps?) more > > feasibly, a user might mix hugetlb and anon pages. So I think that'd be too > > restrictive here. > > Yeah, I agree we should not add a broad single-vma restriction to > GUP. It turns any split of a VMA into a potentially uABI breaking > change and we just don't need that headache in the mm.. > > > I do like the idea of a FOLL_SINGLE_VMA for other use cases though, the > > majority of which want one and one page only. Perhaps worth taking the > > helper added in this series (get_user_page_vma_remote() from [1]) and > > replacing it with an a full GUP function which has an interface explicitly > > for this common single page/vma case. > > Like I showed in another thread a function signature that can only do > one page and also returns the VMA would force it to be used properly > and we don't need a FOLL flag. > Indeed the latest spin of the series uses this. The point is by doing so we can use per-VMA locks for a common case, I was thinking perhaps as a separate function call (or perhaps just reusing the wrapper). This would be entirely separate to all the other work. > Jason