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Mon, 3 May 2021 18:31:27 +0000 Received: from [10.2.50.162] (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 3 May 2021 18:31:27 +0000 Subject: Re: [PATCH 04/16] PCI/P2PDMA: Refactor pci_p2pdma_map_type() to take pagmap and device To: Logan Gunthorpe , , , , , , CC: Stephen Bates , Christoph Hellwig , Dan Williams , Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy References: <20210408170123.8788-1-logang@deltatee.com> <20210408170123.8788-5-logang@deltatee.com> From: John Hubbard Message-ID: Date: Mon, 3 May 2021 11:31:26 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.145.6] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 4f71ab17-7629-46c3-d0de-08d90e61aa29 X-MS-TrafficTypeDiagnostic: CH2PR12MB4326: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:5516; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 May 2021 18:31:27.8060 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4f71ab17-7629-46c3-d0de-08d90e61aa29 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT039.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4326 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 5/3/21 9:30 AM, Logan Gunthorpe wrote: > > > On 2021-05-02 2:41 p.m., John Hubbard wrote: >> On 4/8/21 10:01 AM, Logan Gunthorpe wrote: >>> All callers of pci_p2pdma_map_type() have a struct dev_pgmap and a >>> struct device (of the client doing the DMA transfer). Thus move the >>> conversion to struct pci_devs for the provider and client into this >>> function. >> >> Actually, this is the wrong direction to go! All of these pre-existing >> pci_*() functions have a small problem already: they are dealing with >> struct device, instead of struct pci_dev. And so refactoring should be >> pushing the conversion to pci_dev *up* the calling stack, not lower as >> the patch here proposes. >> >> Also, there is no improvement in clarity by passing in (pgmap, dev) >> instead of the previous (provider, client). Now you have to do more type >> checking in the leaf function, which is another indication of a problem. >> >> Let's go that direction, please? Just convert to pci_dev much higher in >> the calling stack, and you'll find that everything fits together better. >> And it's OK to pass in extra params if that turns out to be necessary, >> after all. > > No, I disagree with this and it seems a bit confused. This change is I am not confused here, no. Other places, yes, but not at this moment. :) > allowing callers to call the function with what they have and doing more > checks inside the called function. This allows for *less* checks in the > leaf function, not more checks. (I mean, look at the patch itself, it > puts a bunch of checks in both call sites into the callee and makes the > code a lot cleaner -- it's removing more lines than it adds). > > Similar argument can be made with the pci_p2pdma_distance_many() (which > I assume you are referring to). If the function took struct pci_dev > instead of struct device, every caller would need to do all checks and > conversions to struct pci_dev. That is not an improvement. > IMHO, it is better to have all of the pci_*() functions dealing with pci_dev instead of dev, but it is also true that this is a larger change, so I won't press the point too hard right now. The reason I commented was that this refactoring goes in the opposite direction that I would be going in, if I were to start "improving" this part of the kernel, via refactoring. Anyway, I'll leave it alone. thanks, -- John Hubbard NVIDIA