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Message-ID: <ZGSFYNAauVDsb22o@infradead.org> Date: Wed, 17 May 2023 00:42:24 -0700 From: Christoph Hellwig <hch@...radead.org> To: Jan Kara <jack@...e.cz> Cc: Lorenzo Stoakes <lstoakes@...il.com>, Jason Gunthorpe <jgg@...dia.com>, "Kirill A . Shutemov" <kirill@...temov.name>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, Leon Romanovsky <leon@...nel.org>, Christian Benvenuti <benve@...co.com>, Nelson Escobar <neescoba@...co.com>, Bernard Metzler <bmt@...ich.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Bjorn Topel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Christian Brauner <brauner@...nel.org>, Richard Cochran <richardcochran@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>, John Hubbard <jhubbard@...dia.com>, Pavel Begunkov <asml.silence@...il.com>, Mika Penttila <mpenttil@...hat.com>, David Hildenbrand <david@...hat.com>, Dave Chinner <david@...morbit.com>, Theodore Ts'o <tytso@....edu>, Peter Xu <peterx@...hat.com>, Matthew Rosato <mjrosato@...ux.ibm.com>, "Paul E . McKenney" <paulmck@...nel.org>, Christian Borntraeger <borntraeger@...ux.ibm.com> Subject: Re: [PATCH v9 0/3] mm/gup: disallow GUP writing to file-backed mappings by default 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.
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