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Shutemov" To: Jesper Dangaard Brouer Cc: netdev@vger.kernel.org, linux-mm@kvack.org, Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= , Ilias Apalodimas , willy@infradead.org, Saeed Mahameed , Alexander Duyck , Andrew Morton , mgorman@techsingularity.net, "David S. Miller" , Tariq Toukan Subject: Re: [net-next PATCH V3 1/3] mm: add dma_addr_t to struct page Message-ID: <20200429003843.rh2pasek7v5o3h63@box> References: <155002290134.5597.6544755780651689517.stgit@firesoul> <155002294008.5597.13759027075590385810.stgit@firesoul> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155002294008.5597.13759027075590385810.stgit@firesoul> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Feb 13, 2019 at 02:55:40AM +0100, Jesper Dangaard Brouer wrote: > The page_pool API is using page->private to store DMA addresses. > As pointed out by David Miller we can't use that on 32-bit architectures > with 64-bit DMA > > This patch adds a new dma_addr_t struct to allow storing DMA addresses > > Signed-off-by: Jesper Dangaard Brouer > Signed-off-by: Ilias Apalodimas > Acked-by: Andrew Morton > --- > include/linux/mm_types.h | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 2c471a2c43fa..0a36a22228e7 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -95,6 +95,13 @@ struct page { > */ > unsigned long private; > }; > + struct { /* page_pool used by netstack */ > + /** > + * @dma_addr: might require a 64-bit value even on > + * 32-bit architectures. > + */ > + dma_addr_t dma_addr; > + }; [ I'm slow, but I've just noticed this change into struct page. ] Is there a change that the dma_addr would have bit 0 set? If yes it may lead to false-positive PageTail() and really strange behaviour. I think it's better to put some padding into the struct to avoid aliasing to compound_head. See commit 1d798ca3f164 ("mm: make compound_head() robust") for context. > struct { /* slab, slob and slub */ > union { > struct list_head slab_list; /* uses lru */ > -- Kirill A. Shutemov