From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 519D828CF6D for ; Tue, 22 Jul 2025 05:53:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753163626; cv=none; b=Z8SVVRnxd+8vEOl86bCkzlhKvic4rnhdCEpvyCps4qB/U0VW8YKSsQg0mIA1yHTIpECUnZmmOywk5stjWyDXohAxSLUMJJTuWjXAOttfiSw+bnmYkk7xSL9FufuDpzaSrM7+rGN8+8PFXISeDLU6yn8fSRKgmbI6ACsrT++Qt9c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753163626; c=relaxed/simple; bh=8P88nmybSdt6par1HmuSfKl0o1ivIxV0cYgSGht2lzM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uISyKqtkpixSj3Rb+zKMBn/LqoA5mLjdyG99dA32J/0LomizDPa8BwuDP0gCGO4CvMcOLKIdno3MU48y0JzXuRaFpkjd7wbtE96XRGUDHMcPVmE4T/AZAEajkILKAQmXkctrEO2IkWVdMsiiuSecL/BxjVOepVT7ywPPX4athb4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de 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> Precedence: bulk X-Mailing-List: linux-block@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: User-Agent: Mutt/1.5.17 (2007-11-01) 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.