From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C40C8830; Wed, 17 May 2023 07:42:33 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3478B1BF; Wed, 17 May 2023 00:42:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HPDWw34wuVd8ioS24/GeMKLCeS2AVAgFryvQOngyNIQ=; b=MsacaJGq7G6gp1g2tKwWD9aPxj lIWiYSjSeZTbTQc8SB3TDcwvIoK1SbqwWRIlPhC4YSIUXLoxKBxmBJ58tJRS9JpJmnWpamWhDDysS V+k9SiF1Gr/FG74fEbS0WLGg5+wM8WHBsWbZPUbLL61ZV6/WLTgCmsVZQ0eHVUJ6f5q8AhU/DBoow 9bum13Vokx8ry+6dEIpVmJ8nUJYyawYXr4VnZAj+bk7J7JugOSOwIcYMLgnY3TWJ9XtR7iQY9Doiw wbuan1SLeZK8/F+6tjRql9ysljB4YE9pY/nSPiZeshU2J/+GFfaBZVfQ90285TEWrjn1EYa4PYQ/M 3YyGF0Jg==; Received: from hch by bombadil.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1pzBnk-008iGg-1Y; Wed, 17 May 2023 07:42:24 +0000 Date: Wed, 17 May 2023 00:42:24 -0700 From: Christoph Hellwig To: Jan Kara Cc: Lorenzo Stoakes , Jason Gunthorpe , "Kirill A . 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> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_NONE,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net 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.