From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 888E825228C; Sun, 23 Aug 2026 13:48:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787492912; cv=none; b=edEbZHl8//VIwEYrcqQGQ919jWnEY7UMsv/lPB/ctear3rbehN8C8ouM/HNx7GgysbbDaDAZ38qLeJ17SGYlw1HNdzMkbXqu474HsYbP6Aj493AGWIvFoGkBMfd1JIE2eRCMEVLfgTZR8wHXeob/2ljP9cx/Zwtemmstw3nH9fI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787492912; c=relaxed/simple; bh=9ru4Rv2kov9P62kZ/7ysWJt78Y4b9QKk4O0YK/oV4/U=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=YXbz6BkMJFQWsS3t5nLLMna1cvtCqx0P4CfT0EKjhjX/SpwYZsDsjdu0e26PlP/ShrjUGdySSrGYgUrhQ9ehn00/l5omnvWuiK2c0IKLysjD31Jv2FkFE3SAJOgx1mPRVMuYYKwyObwKRTf9kq/te4wOvbXt9Ly5cZRWbbyU6vI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L+rXEwaA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="L+rXEwaA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E7D41F000E9; Sun, 23 Aug 2026 13:48:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787492911; bh=3JeIdopILG7DTn8uxHRNJFoP0IqDAq0P8ZuIURtx1Ss=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=L+rXEwaAvrEdOuDK5MJMA8OdE1FlZCAQ38ckVcgZ7N/oK10q5vnR1OXkQJ1AWQexi j8ZEOEt4+1RD70c1XY89BlkmkrmP2xLafzilR1D0xTM7IQVIg2lBIL8zOPNq70bqIE OublJ+DJG0+N2/fasHfbfoQYXMX/rPI5yQ52pBsDWkTh+Sof+SeGNCHMZPPeQbvQkV 2URRyY2I7ygphGHaibJJKtR9gD42gbvJVVSPc+oWN9+5kQ4dbfghF2SMgO0tXPSiZI 3OvodDHFKNmQ+dGMKC5xT4F1CdONR2kTyQ9bOB9v9emYnkxryQApXT6ZMBnYpxaT34 VJwpz9KeqOnpg== Message-ID: Subject: Re: [PATCH V12 02/12] famfs: Module operations, fs_context, and mount From: Jeff Layton To: "Darrick J. Wong" , Miklos Szeredi Cc: "David Hildenbrand (Arm)" , Christian Brauner , John Groves , John Groves , Dan Williams , Bernd Schubert , Alison Schofield , John Groves , Jonathan Corbet , Jake Edge , Shuah Khan , Vishal Verma , Dave Jiang , Matthew Wilcox , Jan Kara , Alexander Viro , Randy Dunlap , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Gregory Price , Andrew Morton , Namjae Jeon , Lorenzo Stoakes , Greg Kroah-Hartman , Ira Weiny , Pasha Tatashin , Haren Myneni , Pratyush Yadav , Giovanni Cabiddu , Jiri Slaby , Ethan Nelson-Moore , Gabriel Whigham , 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" , "fuse-devel@lists.linux.dev" Date: Sun, 23 Aug 2026 09:48:25 -0400 In-Reply-To: <20260822002111.GA6110@frogsfrogsfrogs> References: <0100019fc572ca94-ec363dd7-3a77-484b-b4b7-f2503a0931a6-000000@email.amazonses.com> <20260803022828.75776-1-john@jagalactic.com> <0100019fc5739e5d-bc002300-eede-4c40-9ca8-a277b754496e-000000@email.amazonses.com> <20260806043712.GB3560084@frogsfrogsfrogs> <20260811-baugebiet-hofiert-fanden-3354f4a5e820@brauner> <20260822002111.GA6110@frogsfrogsfrogs> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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Wong wrote: > On Fri, Aug 21, 2026 at 09:39:26PM +0200, Miklos Szeredi wrote: > > On Fri, 21 Aug 2026 at 13:40, David Hildenbrand (Arm) wrote: > >=20 > > > (a) Whether a fuse-based approach is feasible. > > >=20 > > > Are there any major blockers remaining? > >=20 > > No. > >=20 > > > (b) Whether a fuse-based approach is inefficient. > > >=20 > > > Are there scenarios remaining where performance or metadata overh= ead would > > > be bad without an easy way to improve the situation? > >=20 > > Lookups can be cached, extent mappings can also be cached. After the > > inode is in cache and the mapping is set up zero requests are needed > > for open/mmap/read/write/close. > >=20 > > > (c) Whether a fuse-based approach is a bad conceptual fit. > > >=20 > > > Will fuse have to carry a lot of famfs special sauce that cannot > > > really be used elsewhere / generalized? > >=20 > > None. > >=20 > > But "can" and "will" are not the same. The striping code might not be > > very useful outside of famfs. > >=20 > > > (d) Whether a fuse-based approach is too invasive. > > >=20 > > > Will fuse extensions to support famfs actually make it harder to = maintain or > > > slower on some paths? > >=20 > > No. > >=20 > > > (e) Whether a fuse-based approach will make famfs harder to extend. > > >=20 > > > Is there known follow-up work that will be hard/impossible to mod= el in fuse? > >=20 > > It would actually make famfs much easier to extend, since the > > directory structure, metadata, etc. is now controllable within the > > userspace server. > >=20 > > > (f) Whether a fuse-based approach will reduce maintenance effor > > >=20 > > > Will maintaining fuse extensions possibly be harder than maintain= ing > > > standalone famfs? > >=20 > > Testing is a key point. Famfs needs special hardware or emulation, so > > it's not straightforward to test. This could be solved by adding a > > "dummy" mode to famfs server that exercises the same fuse API, but > > instead of special hardware would just use plain memory. > >=20 > > > (g) Whether a fuse-based approach would make famfs more complex. > > >=20 > > > Will the shift to user space result in a significantly more compl= icated > > > overall solution that must be maintained? > >=20 > > The server would be somewhat more complex, since it's now implementing > > things like pathname lookup, etc. But the other stuff (managing file > > maps) should be very similar. > >=20 > > > (h) Who would help drive the fuse approach? > > >=20 > > > Fuse people seem to be willing to help, but I expect that there m= ust be a > > > close cooperation with John to make this fly. I don't expect that= John > > > himself can easily (or understandably wants to :) ) do the heavy = fuse > > > lifting. > >=20 > > Yes, this is where previous efforts seem to have gone off the rails. > > So I agree to take responsibility for implementing the kernel side and > > help with the server side on the condition that John has trust in > > this. I'm not promising -7.4, but can at least try. > >=20 > > Without John's trust I'm not taking this on. >=20 > Whatever path you and John decide on, I would very much like to see the > question of Which famfs driver do we merge? to be resolved for 7.4. >=20 Agreed -- this is exactly my take as well. While I sent a R-b for John's standalone work, I've no issue if the better path forward is deemed to be FUSE. I'd just like to see this come to some sort of resolution. Cheers, --=20 Jeff Layton