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See http://www.infradead.org/rpr.html X-Stat-Signature: mhs8jycijpiwphmjpbm59jnkscibjkfq X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EC34E12000D X-Rspam-User: X-HE-Tag: 1684907740-927333 X-HE-Meta: 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 HnYYZz+L DB3VRqt5I/pVmDoGVWECcTVw89dCUuiL+ENHzNcg24iemQt1CiQ4f6Y0KPGdpa9yNdL0gNJdA0FKfvSF2lHEKrfhLhh/Ua0AxVaU/uksxIL2x5baw8M3FC6BBtftlUeP33EQfCwnsJqjBoK3EmXqJZqQVI8rLL4L1nAMiPtBdCiwuwEyFClE/VYw+8rltd0RviEVjRWjaEmD4EpAY/XJlIOrHP1sYaxELdg6SQld/+oL7H7e/X0AZiIq7RDSmGhUu1cwh6DTWL+GQWG/H+PGcQmqeEvbvGUSC0W+UbXFx0V+8ZNPrc+JEmUidTy+wkwoGI5qewletlPCI0cupkAFo/PljkplJzYvNGObafib9eIKIQvBkBmM7xEBc7ar7MhgbI/vhy5/feAgV0DM= 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 Tue, May 23, 2023 at 09:16:11PM +0100, David Howells wrote: > I've been poking at it this afternoon, but it doesn't look like it's going to > be straightforward, unfortunately. The mm folks have been withdrawing access > to the pinning API behind the ramparts of the mm/ dir. Further, the dio code > will (I think), under some circumstances, arbitrarily insert the zero_page > into a list of things that are maybe pinned or maybe unpinned, but I can (I > think) also be given a pinned zero_page from the GUP code if the page tables > point to one and a DIO-write is requested - so just doing if page == zero_page > isn't sufficient. Yes. I think the proper workaround is to add a MM helper that just pins a single page and make it available to direct-io.c. It should not be exported and clearly marked to not be used in new code. > What I'd like to do is to make the GUP code not take a ref on the zero_page > if, say, FOLL_DONT_PIN_ZEROPAGE is passed in, and then make the bio cleanup > code always ignore the zero_page. I don't think that'll work, as we can't mix different pin vs get types in a bio. And that's really a good thing. > Something that I noticed is that the dio code seems to wangle to page bits on > the target pages for a DIO-read, which seems odd, but I'm not sure I fully > understand the code yet. I don't understand this sentence.