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Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Andrew Lunn , Gerd Hoffmann , Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Shuah Khan , Jason Gunthorpe , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linux-media@vger.kernel.org" , "linaro-mm-sig@lists.linaro.org" , "linux-kselftest@vger.kernel.org" , "sdf@fomichev.me" , "razor@blackwall.org" , "daniel@iogearbox.net" , "almasrymina@google.com" , "matttbe@kernel.org" , "skhawaja@google.com" , "dw@davidwei.uk" , Bobby Eshleman Subject: Re: [PATCH net-next v2 2/4] udmabuf: emit one sg entry per pinned folio Message-ID: References: <20260611-tcpdm-large-niovs-v2-0-ee2bf15e7523@meta.com> <20260611-tcpdm-large-niovs-v2-2-ee2bf15e7523@meta.com> Precedence: bulk X-Mailing-List: netdev@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: On Tue, Jun 16, 2026 at 01:57:49PM -0700, Bobby Eshleman wrote: > On Tue, Jun 16, 2026 at 06:04:03AM +0000, Kasireddy, Vivek wrote: > > Adding Jason to this discussion. > > > > Hi Bobby, > > > > > Subject: [PATCH net-next v2 2/4] udmabuf: emit one sg entry per pinned > > > folio > > > > > > From: Bobby Eshleman > > > > > > get_sg_table() emitted one PAGE_SIZE sg entry per page even when the > > > underlying folio was larger. > > > > > > Instead, walk folios[] and emit one sg entry per folio. When folios > > We have recently merged a patch (that will make it into 7.2) from Jason that > > replaced sg_set_folio() with sg_alloc_table_from_pages() in udmabuf driver: > > https://gitlab.freedesktop.org/drm/tip/-/commit/5bf888673e0dda5a53220fa0c4956271a46c353c > > > > Since you are relying on sg_set_folio(), the core argument against its usage > > in udmabuf is that it doesn't work well with offsets > PAGE_SIZE, resulting > > in a malformed scatterlist. Not sure if this can be fixed easily. > > > > > represent large pages (as is for MFD_HUGETLB), each sg entry is a large > > > page. Normal PAGE_SIZE sg tables are unchanged. > > > > > > This is helpful for importers like net/core/devmem that expect dmabuf sg > > IMO, udmabuf needs to detect whether importers can handle segments that > > are > PAGE_SIZE and set the entries appropriately. Please look into how the > > GPU drivers and other dmabuf exporters/importers handle this situation, so > > that we can adopt best practices to address this issue. > > > > Thanks, > > Vivek > > Hey Vivek, > > It sounds looks like that patch might solve my problem. I'll apply and > troubleshoot from there. > > Thanks! > > Best, > Bobby Good news for me, that patch solves the problem. Thanks for bringing that up! I can drop my udmabuf patch when I respin the series. Best, Bobby