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Message-ID: <CAC_iWjJQepZWVrY8BHgGgRVS1V_fTtGe-i=r8X5z465td3TvbA@mail.gmail.com> Date: Thu, 17 Aug 2023 19:59:37 +0300 From: Ilias Apalodimas <ilias.apalodimas@...aro.org> To: Jakub Kicinski <kuba@...nel.org> Cc: Mina Almasry <almasrymina@...gle.com>, Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net, pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Lorenzo Bianconi <lorenzo@...nel.org>, Alexander Duyck <alexander.duyck@...il.com>, Liang Chen <liangchen.linux@...il.com>, Alexander Lobakin <aleksander.lobakin@...el.com>, Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Jesper Dangaard Brouer <hawk@...nel.org> Subject: Re: [PATCH net-next v7 1/6] page_pool: frag API support for 32-bit arch with 64-bit DMA Hi Jakub, On Thu, 17 Aug 2023 at 19:15, Jakub Kicinski <kuba@...nel.org> wrote: > > On Thu, 17 Aug 2023 16:57:16 +0300 Ilias Apalodimas wrote: > > Why should we care about this? Even an architecture that's 32-bit and > > has a 64bit DMA should be allowed to split the pages internally if it > > decides to do so. The trick that drivers usually do is elevate the > > page refcnt and deal with that internally. > > Can we assume the DMA mapping of page pool is page aligned? We should > be, right? Yes > That means we're storing 12 bits of 0 at the lower end. > So even with 32b of space we can easily store addresses for 32b+12b => > 16TB of memory. "Ought to be enough" to paraphrase Bill G, and the > problem is only in our heads? Do you mean moving the pp_frag_count there? I was questioning the need to have PP_FLAG_PAGE_SPLIT_IN_DRIVER overall. With Yunshengs patches such a platform would allocate a page, so why should we prevent it from splitting it internally? Thanks /Ilias > > Before we go that way - Mina, are the dma-buf "chunks" you're working > with going to be fragment-able? Or rather can driver and/or core take > multiple references on a single buffer?
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