From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 CF246148850; Fri, 17 Apr 2026 08:13:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776413633; cv=none; b=L9wieWnDhAIziASz5uFaS4SsdpWs5htDTCNvRVjd84CoKuo3qMdCTEtSQZhPo5u8aQ4gTSFrCPde0oaRiIsnlRVrcmo5vckZzNimytSElYQb/tIcRHpcIVLv6RJvSsFaQsfS4KlXsxtB3rxHMDynPccf3fWfR8mLuSYap1DiNaI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776413633; c=relaxed/simple; bh=AB7kM5+zl3g8v3ZilOIEtTC6f3PJQWJBnG4VUhc+iZY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pgOCuvSL5BwA67HCtHykKaxblnqVFCc1/r2toPDdEWghRdmamzOI7Ffl0kO29vlJvxrQfayNLcitMSfdsNB3ZaX48yVYvMTpTCRnbY1FIgYoemQiw6WYQAlBw5eK/XHygjehnmEJJWzHvJ94zeGmfM4h+8JJ9S+kWcMrMAKxNvQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=WiUBalMv; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WiUBalMv" 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=FzPtR8XBpYAtdtjQmCJHfr8Ak8KPMG6rRy1FtmV/4Ek=; b=WiUBalMv2ap5OVbiLawUg65FpJ pNR7afCUfM1Y5H54gD+mxP8FYdeUTwkkA0bT3lpL+c2tHtDjv+GO30fdIjntRTwTbAd8Ac7v6SlHG lqWz8sQrCTNB4Ep8rwbbWG4pbA7aV+GFKeiZJB77GSFPS8eReDRblh7k8h7G6m2tu+qF6HCe9R9IA GfbsHW+OdCKYCTzghN0ZunI2/qjjk5OhnzOg4tETYlXD81TCs8hZLXOGYe9ljt3UkAVvJU0CbNX6o x5sep4jdX3jQXeY7TS15OBgmnyfO4hgqG348n4PVarvlmqSUYt+ZuPwizux3jrEhwKNss9LcOpUbe vgKRI+UQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wDeKW-00000003erK-0sn1; Fri, 17 Apr 2026 08:13:36 +0000 Date: Fri, 17 Apr 2026 01:13:36 -0700 From: Christoph Hellwig To: "Darrick J. Wong" Cc: Dan Williams , Gregory Price , Joanne Koong , John Groves , Miklos Szeredi , Bernd Schubert , John Groves , Dan J 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" Subject: Re: [PATCH V10 00/10] famfs: port into fuse Message-ID: References: <20260414185740.GA604658@frogsfrogsfrogs> <43d36427-4629-4712-a262-391e64006eb5@app.fastmail.com> <20260416224331.GD114184@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: <20260416224331.GD114184@frogsfrogsfrogs> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Thu, Apr 16, 2026 at 03:43:31PM -0700, Darrick J. Wong wrote: > ...the memory interleaving is a rather interesting quality of famfs. > There's no good way to express a formulaic meta-mapping in traditional > iomap parlance, and famfs needs that to interleave across memory > controllers/dimm boxen/whatever. Throwing individual iomaps at the > kernel is a very inefficient way to do that. So I don't think there's a > good reason to get rid of GET_FMAP at this time... Why no? We can triviall make an iomap point to multiple backing devices and throw in a stride/offset. That would make btrfs striping (and non-degraded parity RAID reads) a lot more efficient. > ...however the strongest case (IMO) would be if (having merged famfs) we > then merge fuse-iomap after famfs. Then we extend the existing > fuse-iomap-bpf prototype to allow per-mount and per-inode iomap bpf ops. > That enables us to analyze thoroughly the performance characteristics of: Don't go there. I think that you two are comining up with two interfaces for roughly the same thing is a pretty clear indicator that this needs to be fully hashed out as a single interface first, and any kind of preliminary merging is just going to create problems.