From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 4964526B755; Mon, 26 Jan 2026 20:40:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460058; cv=none; b=lGxXtX6szmWoG9V4mOPwH7xYLjI4elJb1ZgfuNrMSoNsRNfs1OSNc/kbMOJx+vtfnrcFFAjslanOexo9xW7BPQEijn5/4katfIqhwYblKfuh6jZPVVWtI1GBZ01DPA5IPMHkFRFHXcq7NsaH8ndqftyCnQhjgBRau4aKRVuGyMY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460058; c=relaxed/simple; bh=hyalMSb8PkIB/y2wTEkvrXTVerDXEWCMzBnanNpHbcI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tJD3d//LhpkXMkNCBzC2H4ep62yNVwC45t5puw0VPo4X9KnpNqjv79TT31UxrzsZONXqKDUDL6e1SxzPypNqQoYWoLodGWIs7Xy/XhAQYFR0etY5P4Nc+I1hoxsyLErhDT+vDpN38O/nm/LCL0J52vntMDlBZERc8icd3Mp4doM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Oyacvg75; arc=none smtp.client-ip=90.155.50.34 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=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Oyacvg75" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=VYfYU993elGtunsD0W2WH0r2p/2SUda3jsdLQYQD3EA=; b=Oyacvg75LKtsjDOv37VDWNhVPp zis4lf5BP+nDmagFci+X/6fike3iOQSw0H6n47gU48W8ZY9JYNcRhSUVNZ5GZy+9BQevh545F6nCA xzjeM6C0TVRLIzbldWywJyQeY7i4tGglILFnWtakKFzHrFDQrvSds4mWVPXGVuuhkAotAAUbFsPga MO8KKC6wSBwovG9CIfmilaUabdJm1C0Ifwp9CxzLGHpFMBqNMmWpwuG05vi1TiUTClIB8Pw1VG8eJ 1UNqylNL+2FHNFIVNOZXMZI9W/6dWPhMZaDIbqWyfhJCftpNawrpxBDovBRa6BHUtyCHCFkk3Zs44 ShPEyclw==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vkTOE-00000006RuR-3w1z; Mon, 26 Jan 2026 20:40:51 +0000 Date: Mon, 26 Jan 2026 20:40:50 +0000 From: Matthew Wilcox To: Cong Wang Cc: Gao Xiang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Cong Wang , multikernel@lists.linux.dev Subject: Re: [ANNOUNCE] DAXFS: A zero-copy, dmabuf-friendly filesystem for shared memory Message-ID: References: <55e3d9f6-50d2-48c0-b7e3-fb1c144cf3e8@linux.alibaba.com> Precedence: bulk X-Mailing-List: multikernel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jan 26, 2026 at 11:48:20AM -0800, Cong Wang wrote: > Specifically for this scenario, struct inode is not compatible. This > could rule out a lot of existing filesystems, except read-only ones. I don't think you understand that there's a difference between *on disk* inode and *in core* inode. Compare and contrast struct ext2_inode and struct inode. > Now back to EROFS, it is still based on a block device, which > itself can't be shared among different kernels. ramdax is actually > a perfect example here, its label_area can't be shared among > different kernels. > > Let's take one step back: even if we really could share a device > with multiple kernels, it still could not share the memory footprint, > with DAX + EROFS, we would still get: > 1) Each kernel creates its own DAX mappings > 2) And faults pages independently > > There is no cross-kernel page sharing accounting. > > I hope this makes sense. No, it doesn't. I'm not suggesting that you use erofs unchanged, I'm suggesting that you modify erofs to support your needs.