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 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.lore.kernel.org (Postfix) with ESMTPS id E32B3C83F1A for ; Tue, 22 Jul 2025 05:57:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Kry8fcora5aaZe57efVkCvytS5S90yVJ9IiGZOOnjk4=; b=rkmq9Ge8debzEvlWdvzMz3fBDg JoTnD01d2D7821+gKqdO5zLOCWfjCcfdEJ2IUuLU/oGW3WIG04kyclMJbaxpYfszT16qGmKZJibM9 zKgU4xUv7UBffF/5LIGkU1xjW/jb4cmBE65DBg6bEQH27ibY+iDdqUYd+H4UWFb8+YfdX/c7GzHVq byWpSrwbJADoG22tNVsogSCfwii9RR4LeByEL/6hybMK7srmvMWT6TbkHZ6my8EotQd5jDrNWUTNd R7xBpReJTWPbam0EW109j3PjKrK+pXsseRAAdRRDF2orCPkYyCeaehE5oVAPRiffP788HPmhHLgB6 r2W4CagQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1ue60H-00000001NRv-3S2g; Tue, 22 Jul 2025 05:57:29 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1ue5wf-00000001N2h-1WCX for linux-nvme@lists.infradead.org; Tue, 22 Jul 2025 05:53:46 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 9AC0768AA6; Tue, 22 Jul 2025 07:53:39 +0200 (CEST) Date: Tue, 22 Jul 2025 07:53:39 +0200 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , Keith Busch , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, axboe@kernel.dk, leonro@nvidia.com Subject: Re: [PATCHv2 1/7] blk-mq-dma: move the bio and bvec_iter to blk_dma_iter Message-ID: <20250722055339.GB13634@lst.de> References: <20250720184040.2402790-1-kbusch@meta.com> <20250720184040.2402790-2-kbusch@meta.com> <20250721074223.GF32034@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250721_225345_681209_40CAD0B2 X-CRM114-Status: GOOD ( 22.43 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, Jul 21, 2025 at 08:33:02PM -0600, Keith Busch wrote: > On Mon, Jul 21, 2025 at 09:42:23AM +0200, Christoph Hellwig wrote: > > On Sun, Jul 20, 2025 at 11:40:34AM -0700, Keith Busch wrote: > > > From: Keith Busch > > > > > > The req_iterator just happens to have a similar fields to what the dma > > > iterator needs, but we're not necessarily iterating a bio_vec here. Have > > > the dma iterator define its private fields directly. It also helps to > > > remove eyesores like "iter->iter.iter". > > > > Going back to this after looking at the later patches. The level > > for which this iter exists is only called blk_map_* as there is > > nothing dma specific about, just mapping to physical addresses. > > > > So maybe call it blk_map_iter instead? > > But the structure yields "dma_addr_t" type values to the consumer. > Whether those are physical addresses or remapped io virtual addresses, > they're still used for direct memory access, so I think the name as-is > is a pretty good fit. There's two layers: The lower layer implemented by blk_map_iter_next just yields a phys_vec. The upper layer built on top does the dma mapping in case of the new blk_rq_dma_map_iter_start / blk_rq_dma_map_iter_next API. But in case of the old __blk_rq_map_sg API it doesn't even directly do the DMA mapping yet. And some drivers at least historically used the blk_map_sg without then doing a DMA mapping, either for MMIO or platform specific things using physical address. My hope was to eventually migrate them to use blk_map_iter_next.