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[71.191.243.150]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ac84cb0474sm132683506d6.40.2026.04.14.15.20.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2026 15:20:40 -0700 (PDT) Date: Tue, 14 Apr 2026 18:20:37 -0400 From: Gregory Price To: "Darrick J. Wong" Cc: John Groves , Miklos Szeredi , Joanne Koong , Bernd Schubert , John Groves , Dan Williams , Bernd Schubert , Alison Schofield , John Groves , Jonathan Corbet , Shuah Khan , Vishal Verma , Dave Jiang , Matthew Wilcox , Jan Kara , Alexander Viro , David Hildenbrand , Christian Brauner , Randy Dunlap , Jeff Layton , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Aravind Ramesh , Ajay Joshi , "venkataravis@micron.com" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "nvdimm@lists.linux.dev" , "linux-cxl@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , djbw@kernel.org Subject: Re: [PATCH V10 00/10] famfs: port into fuse Message-ID: References: <20260331123702.35052-1-john@jagalactic.com> <0100019d43e5f632-f5862a3e-361c-4b54-a9a6-96c242a8f17a-000000@email.amazonses.com> <38744253-efa3-41c5-a491-b177a4a4c835@bsbernd.com> <20260414185740.GA604658@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260414185740.GA604658@frogsfrogsfrogs> On Tue, Apr 14, 2026 at 11:57:40AM -0700, Darrick J. Wong wrote: > > > > I very strongly object to making this a prerequisite to merging. This > > is an untested idea that will certainly delay us by at least a couple > > of merge windows when products are shipping now, and the existing approach > > has been in circulation for a long time. It is TOO LATE!!!!!! > ... > > That said, you're clearly pissed at the goalposts changing yet again, > and that's really not fair that we collectively keep moving them. > This seems a bit more than moving a goalpost. We're now gating working software, for real working hardware, on a novel, unproven BPF ops structure that controls page table mappings on page table faults which would be used by exactly 1 user : FAMFS. And that singular user is harmed because it turns an O(1) offset calculation into a pointer chase - on the hottest path (every fault). John is right to push back here. --- That said - I'm looking at fs/fuse/famfs.c and I'm asking myself what in here is actually famfs-specific. If you just s/FAMFS/DAX/g - the file just reads like a simple DAX-iomap backend with optional striping. Would it be reasonable to refactor the dax layer (and users) to create an ops structure that becomes the basis for the BPF solution? We don't even know what the whole BPF scope is, and it seems wholly unfair to John's and his users to make that solely their problem (for negative value!). ~Gregory