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Ye5Pv90Zz7a8w5CVuCl9o3qoDcACeyLKdR3/rUyOaMsX6QgdG4oir2EL0X+EWOaYG9M+GMOJ/yoLAEKZbraCWUYG/ILN1bWKLnhA3rNTPTC9invXHWjTJcoBtJ0184mPYMO2n4QnUn64ewxhBvbxSmB5XLLRJp1ok/bG+FvPCj1mV/ZBvT5ZK6Zx7Pps92LK99/nRTRDPYX59mMqm3khQ+2eEwGmLG0S5++PTme+ZB2sjasARCd59scPYsfce4QVU0mE5pPu7AsZXpKtbbY7xTKSQzynYVufdvEs5vEDb3n4vR5r794rdzTX2cq9rZJpa7UkNfl4qsDS90pwW15PG49ZHB6eqYzIJtQGvJ4TJESjBUVcStHE/p6ZhsMPD0M/xALt6QsI6cMsVWGYT+ipyL+S2ufZIUVxjKTHoDjSkX42Vsz/nhxET24H8CTR3W/MSjuZkgU4mhAsXDykae7W+WTPF7amoLUnL5EWZgCSDNBOlVLvqg2QLJPI5P3UcHZOeI3zI9HtY0CrMO93dyQz81t4x46SpxKuBFIsdWNqjkaI8s6fDTFr6dwbuFw8tS4/Ex20Z Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24.08.26 18:30, Luigi Rizzo wrote: > On Mon, Aug 24, 2026 at 6:06 PM Robin Murphy wrote: >> >> On 2026-08-24 4:29 pm, Luigi Rizzo wrote: >>> Introduce swiotlb_alloc_pages() and swiotlb_free_pages() to allocate >>> and release compound pages directly from the default SWIOTLB pool. >> >> Huh? The sole intended purpose of SWIOTLB is for bounce-buffering data >> which already exists in some other memory that is unsuitable for DMA for >> whatever reason. If you want to allocate directly from some kind of >> pre-shared DMA page pool to avoid bounce-buffering, set up some kind of >> pre-shared DMA page pool and allocate from that in a manner which can >> avoid bouncing entirely (see DMA_ATTR_CC_SHARED). The idea of getting as >> far as calling swiotlb_bounce() to then have a special case saying "haha >> not really" seems entirely absurd. Don't hack stuff into the SWIOTLB >> code which has no business being there. > > Ah I see DMA_ATTR_CC_SHARED did not exist when I implemented the > swiotlb allocator. Cool, one less piece, it should be possible to replace > this chunk witth the DMA_ATTR_CC_SHARED. > I agree with Robin's point (if I understood it correctly): Why should it at all pass through the SWIOTLB? Why can't it be a standalone DMA pool? > The other pieces are still relevant though ? > > - use these dma-able pages for page pool allocations (small) > - [PATCH v2 3/5] net/swiotlb: Track bounce device per socket > or one would have to unconditionally allocate from that pool, > even for e.g. local sockets > - divert socket allocations for eligible sockets to a DMA-able pool > Thanks, Dragos