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Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , John Hubbard , Pavel Begunkov , Mika Penttila , David Hildenbrand , Dave Chinner , Theodore Ts'o , Peter Xu , Matthew Rosato , "Paul E . McKenney" , Christian Borntraeger Subject: Re: [PATCH v9 0/3] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: References: <20230515110315.uqifqgqkzcrrrubv@box.shutemov.name> <7f6dbe36-88f2-468e-83c1-c97e666d8317@lucifer.local> <20230517072920.bfs7gfo4whdmi6ay@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230517072920.bfs7gfo4whdmi6ay@quack3> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Stat-Signature: tq6mo97bd935c9gqicecmnkouqjsm79c X-Rspam-User: X-Rspamd-Queue-Id: 165D840005 X-Rspamd-Server: rspam07 X-HE-Tag: 1684309350-12223 X-HE-Meta: U2FsdGVkX19Ev4xJyWA8SYKloz2aTX4LV1yQSvzt21gHqeHhtVP38ht6QzuRm94XWFZh10M67PjKrRmdmNz8k97sM+IhkJIb7Aqzx6RlqEjbNS0VHqYNC9P3K+0CBR7c5wpoZWaOQQZdRJsji7wvW09qndF5ZR7AU05AEKt9nivgOF9ZmhY+0USRDx6jWFSrVCCeQ99kDFx7biddZcB4iePY/o9V5+8IcFBKgNmHqeGf2Myxh7UH10sjiIaG+VxVMn5gF6KI+o7LUgLT0zCAyQ7Fq8hTDri7QpYYTBXLwV0PtQFOpEZbyem1LHwc05CmEsIab0YzSsXEQTuRCIsrm18+ChJemBeT4rqoX3yCVT9N2qFryHdcQRZ2cnetTGaZ8Hc4XKJKs0gPeD+m3Yjjd/4DAcwugKy+/wm0TJwkzG3Rit8bjjjwxUFvzz/Xisre1JowALSQ8sbExOf6tfDzvFp+ipRCL8S6NgOl0opennSFXDAN6oyz4wn8Dz9xfRe+L2z5RUKBgpKbQeRyZh3aRNz+aQSgUtGCRsfqjUb9Ij8uMG+Hv5JZawWm/IDHZ+UdFF+qG+kACviTn1CzO3ZOBILFOteIaI4/za1ROvRRnlsnnl9U+qWzRzK//4xPsvtptCBZo3xeakgaMnO5ONTIILEm5N1UGOkvEPKqxzU+E2QVcxWDbH1nyb6mf2z0Dw7+X78P3HS8pGMHFBtLjrPGHBruquJS1Df0yGHflbVVQOjl+6j+KzEgCeMNiGiEXffHNkS8AF5VIjPYFcI11mTwTfCwblNr2qWdUeT6iawqItifBxhWIkR8G6lXN8SYKzrl70/lWP0m8a/rI8+gBszxWKgrqeK0ovH970RMqSqHPZ2WpS2uNMPkfEyDL6c8G4hUUo+bj/yObeZoYVNALckq2DDgARiU2EXL5MgWOHRS8qH7T7k1G9+TIIGFWDeByKUgtmDACA3m5OgIZ0/2Epz 75xbPPp9 eRCCIC+jPKKyw+erjoHkuxnY2EUpYDzs+Uy/0csNovBtGThp6eJEs+MKTT65v5+mxUbjmlrzl1nGmeYB1AwAYvpOLi9ZpdncPSCHBILE4PxSA/DO7O50ywpZYzrKbg1lkg0kI7c+3GHzz1jihoNHy86PmBerFI9Sz97ygvYA8qumTD32pNyQZlWEAb3er821ccqnO7kK3HBsxGn6KrOq1v5oa/VMpn9ZQvoVbrTmv4yTcC1QYwoOAyqdVwtvvmkxowAi0Yzyo41+mxRfTVLUYfkGs2flxj8SGQcw/rw6YD6Il156MyDq17s9IjHIBx+3bqjxz3bDW1NSixBwGucXeXiFYneedH+z0mTECh2wGKp5k4PQZmXQxCIKuTJKhMAGoHVSjeX/keW3yc8OgRCJVmCyir8nAk/VFH1gn0PwkBaYVrz6BRk7sKV69gHdNc0YvmVhhRfX6oP6vAlw= 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, May 17, 2023 at 09:29:20AM +0200, Jan Kara wrote: > > > Surely it is, but like Ted said, the FS folks are not interested and > > > they are at least half the solution.. > > > > :'( > > Well, I'd phrase this a bit differently - it is a difficult sell to fs > maintainers that they should significantly complicate writeback code / VFS > with bounce page handling etc. for a thing that is not much used corner > case. So if we can get away with forbiding long-term pins, then that's the > easiest solution. Dealing with short-term pins is easier as we can just > wait for unpinning which is implementable in a localized manner. Full agreement here. The whole concept of supporting writeback for long term mappings does not make much sense. > > > The FS also has to actively not write out the page while it cannot be > > > write protected unless it copies the data to a stable page. The block > > > stack needs the source data to be stable to do checksum/parity/etc > > > stuff. It is a complicated subject. > > > > Yes my sense was that being able to write arbitrarily to these pages _at > > all_ was a big issue, not only the dirty tracking aspect. > > Yes. > > > I guess at some level letting filesystems have such total flexibility as to > > how they implement things leaves us in a difficult position. > > I'm not sure what you mean by "total flexibility" here. In my opinion it is > also about how HW performs checksumming etc. I have no idea what total flexbility is even supposed to be.