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 gsnIN6zp I9GqCuUPPwgC4eL/cLBEFydxySDXoOT8pzDX2y+S0ITXSGkOvIsSNZ9NcVoSwcC1BsCCGStoTcSQrR+mXaUJdKml5+sjJ10MUIcVJOhpfWFUnrNUCNVA/51SypEO1HzxUGK24h4myMskSjZmpmrQjiRui1cXMQzXfqslEC3OCjmxI+RdwfE8Iqz8nk+rLj0VFNzDJ0OFP2zJUwVo9r6sSk1cwgVdKTAXZUQUalDBe6tFsRGd9OVO7QYSUsGwb6NaQNkVnZWjqjoETkPGlmt42kFbBiEKpmyEaPv2puHMymTeso8DY1qmXzyHUmVj8kNWcmJZw/sGcXYLfZLU1ggmneIj6TKtLfA2OdrP3olSqttyV6D4= 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: On Thu, Oct 19, 2023 at 04:53:43PM +0100, Matthew Wilcox wrote: > On Thu, Oct 19, 2023 at 11:25:31AM -0400, Chuck Lever wrote: > > The SunRPC stack manages pages (and eventually, folios) via an > > array of struct biovec items within struct xdr_buf. We have not > > fully committed to replacing the struct page array in xdr_buf > > because, although the socket API supports biovec arrays, the RDMA > > stack uses struct scatterlist rather than struct biovec. > > > > This (incomplete) series explores what it might look like if the > > RDMA core API could support struct biovec array arguments. The > > series compiles on x86, but I haven't tested it further. I'm posting > > early in hopes of starting further discussion. > > Good call, because I think patch 2/9 is a complete non-starter. > > The fundamental problem with scatterlist is that it is both input > and output for the mapping operation. You're replicating this mistake > in a different data structure. Fwiw, I'm not at all wedded to the "copy-and-paste SGL" approach. > My vision for the future is that we have phyr as our input structure. > That looks something like: > > struct phyr { > phys_addr_t start; > size_t len; > }; > > On 32-bit, that's 8 or 12 bytes; on 64-bit it's 16 bytes. This is > better than biovec because biovec is sometimes larger than that, and > it allows specifying IO to memory that does not have a struct page. Passing a folio rather than a page is indeed one of the benefits we would like to gain for SunRPC. > Our output structure can continue being called the scatterlist, but > it needs to go on a diet and look more like: > > struct scatterlist { > dma_addr_t dma_address; > size_t dma_length; > }; > > Getting to this point is going to be a huge amount of work, and I need > to finish folios first. Or somebody else can work on it ;-) I would like to see forward progress, as SunRPC has some skin in this game. I'm happy to contribute code or review. If there is some consensus on your proposed approach, I can start with that. -- Chuck Lever