From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46BAAC5AD49 for ; Tue, 3 Jun 2025 13:19:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D8D316B0448; Tue, 3 Jun 2025 09:19:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D64506B044A; Tue, 3 Jun 2025 09:19:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C7A776B044B; Tue, 3 Jun 2025 09:19:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A5C626B0448 for ; Tue, 3 Jun 2025 09:19:50 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 38D2C1408C2 for ; Tue, 3 Jun 2025 13:19:50 +0000 (UTC) X-FDA: 83514146940.27.8632B58 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf26.hostedemail.com (Postfix) with ESMTP id 2A4A1140013 for ; Tue, 3 Jun 2025 13:19:47 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=Zx62paCd; spf=none (imf26.hostedemail.com: domain of BATV+175a1930472064472083+7954+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+175a1930472064472083+7954+infradead.org+hch@bombadil.srs.infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1748956788; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=IMyZpNPWuRD8Yt0Bj66tbpS5jFHAY+R03rfqd24z1tA=; b=a/0bcu9RyOioxnlvx+d9eDS0cRBrx6kEiLXab8AcBk65+evPbv3yJX5xyxISzdBK6LQcsH rksAEuYAr21vGpfDCnAZgB2LNUsUs9mU0J7/CKYb8sac0QNImD4SqPXS7KnaS2Zw9CTwOn hLEIonCtcoGrteUxOMLEn9H7ZWplkFI= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=Zx62paCd; spf=none (imf26.hostedemail.com: domain of BATV+175a1930472064472083+7954+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+175a1930472064472083+7954+infradead.org+hch@bombadil.srs.infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1748956788; a=rsa-sha256; cv=none; b=O262BZpYcjiZcTSDBsHgA80O89WfELfM4o/81qhgx1XJG+AzvdxqApdP0X5ZfciATCeujw sm2sLVNZ4pRGb1j1dZE3MUaFFqXU4kuJakZiWE2s0V8RhgUYde7RrmD4kpeFVBkmWgeFYi LeUp9woOYyagjLmhBe4NozeZKr4cDAI= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=IMyZpNPWuRD8Yt0Bj66tbpS5jFHAY+R03rfqd24z1tA=; b=Zx62paCdRIfY0a9wF1dF/rAnNo UiHTftfyE+VGyqJw2HuPeDULbIREjlmcy3gsX/PpD0vl91RQKOjPUf80vBJyOYXNYYOvQWp51X0az 28iNgL0C6G1PkGFGA/O/X50dvI586E5cM6uuXdEeMXCnDiGkmWwz+ybw5XaMPcnF04tWsNM2lhXPL qQG+LPDKpcTmCnzRrFrZvTxc/Z2izJLAJvnUt7mQKGQRrzVCedZELM+5pxIeSGdU09pIPsEZQGote dWu2tqnaHPFjDJdBXCVu3HNouwDQ3iB3IQj5QrXprdLj3shYEHJfcAcfjQwRnVrG5PyT3IByVNWjb lOa4UeiA==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uMRYI-0000000B0wB-3pbC; Tue, 03 Jun 2025 13:19:38 +0000 Date: Tue, 3 Jun 2025 06:19:38 -0700 From: Christoph Hellwig To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: Christoph Hellwig , wangtao , sumit.semwal@linaro.org, kraxel@redhat.com, vivek.kasireddy@intel.com, viro@zeniv.linux.org.uk, brauner@kernel.org, hughd@google.com, akpm@linux-foundation.org, amir73il@gmail.com, benjamin.gaignard@collabora.com, Brian.Starkey@arm.com, jstultz@google.com, tjmercier@google.com, jack@suse.cz, baolin.wang@linux.alibaba.com, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, bintian.wang@honor.com, yipengxiang@honor.com, liulu.liu@honor.com, feng.han@honor.com Subject: Re: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range Message-ID: References: <20250603095245.17478-1-tao.wangtao@honor.com> <09c8fb7c-a337-4813-9f44-3a538c4ee8b1@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <09c8fb7c-a337-4813-9f44-3a538c4ee8b1@amd.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2A4A1140013 X-Stat-Signature: msm85cin6i4d7soj5feodnjzfysdkipx X-Rspam-User: X-HE-Tag: 1748956787-252494 X-HE-Meta: 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 B0ZAeMcK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 03, 2025 at 03:14:20PM +0200, Christian König wrote: > On 6/3/25 15:00, Christoph Hellwig wrote: > > This is a really weird interface. No one has yet to explain why dmabuf > > is so special that we can't support direct I/O to it when we can support > > it to otherwise exotic mappings like PCI P2P ones. > > With udmabuf you can do direct I/O, it's just inefficient to walk the > page tables for it when you already have an array of all the folios. Does it matter compared to the I/O in this case? Either way there has been talk (in case of networking implementations) that use a dmabuf as a first class container for lower level I/O. I'd much rather do that than adding odd side interfaces. I.e. have a version of splice that doesn't bother with the pipe, but instead just uses in-kernel direct I/O on one side and dmabuf-provided folios on the other.