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Petersen" , "daniel@iogearbox.net" , Dan Williams , "jack@suse.com" , Zhu Yanjun Subject: Re: [RFC RESEND 00/16] Split IOMMU DMA mapping operation to two steps Message-ID: <20240310093513.GB12921@unreal> References: <20240306154328.GM9225@ziepe.ca> <20240306162022.GB28427@lst.de> <20240306174456.GO9225@ziepe.ca> <20240306221400.GA8663@lst.de> <20240307000036.GP9225@ziepe.ca> <20240307150505.GA28978@lst.de> <20240307210116.GQ9225@ziepe.ca> <20240308164920.GA17991@lst.de> <20240308202342.GZ9225@ziepe.ca> <20240309161418.GA27113@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240309161418.GA27113@lst.de> X-Rspamd-Queue-Id: 2EEF720003 X-Rspam-User: X-Stat-Signature: ibepno1wqw78tjhybaa5ixpxhmf4ofbo X-Rspamd-Server: rspam01 X-HE-Tag: 1710063320-71443 X-HE-Meta: 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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 Sat, Mar 09, 2024 at 05:14:18PM +0100, Christoph Hellwig wrote: > On Fri, Mar 08, 2024 at 04:23:42PM -0400, Jason Gunthorpe wrote: > > > The DMA API callers really need to know what is P2P or not for > > > various reasons. And they should generally have that information > > > available, either from pin_user_pages that needs to special case > > > it or from the in-kernel I/O submitter that build it from P2P and > > > normal memory. > > > > I think that is a BIO thing. RDMA just calls with FOLL_PCI_P2PDMA and > > shoves the resulting page list into in a scattertable. It never checks > > if any returned page is P2P - it has no reason to care. dma_map_sg() > > does all the work. > > Right now it does, but that's not really a good interface. If we have > a pin_user_pages variant that only pins until the next relevant P2P > boundary and tells you about we can significantly simplify the overall > interface. And you will need to have a way to instruct that pin_user_pages() variant to continue anyway, because you asked for FOLL_PCI_P2PDMA. Without that force, you will have !FOLL_PCI_P2PDMA behaviour. When you say "simplify the overall interface", which interface do you mean? Thanks