On Mon, 11 Apr 2016 15:21:26 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > On Mon, Apr 11, 2016 at 11:41:57PM +0200, Jesper Dangaard Brouer wrote: > > > > On Sun, 10 Apr 2016 21:45:47 +0300 Sagi Grimberg <sagi@xxxxxxxxxxx> wrote: > > [...] > > > > > > If we go down this road how about also attaching some driver opaques > > > to the page sets? > > > > That was the ultimate plan... to leave some opaques bytes left in the > > page struct that drivers could use. > > > > In struct page I would need a pointer back to my page_pool struct and a > > page flag. Then, I would need room to store the dma_unmap address. > > (And then some of the usual fields are still needed, like the refcnt, > > and reusing some of the list constructs). And a zero-copy cross-domain > > id. > > I don't think we need to add anything to struct page. > This is supposed to be small cache of dma_mapped pages with lockless access. > It can be implemented as an array or link list where every element > is dma_addr and pointer to page. If it is full, dma_unmap_page+put_page to > send it to back to page allocator. It sounds like the Intel drivers recycle facility, where they split the page into two parts, and keep page in RX-ring, by swapping to other half of page, if page_count(page) is <= 2. Thus, they use the atomic page ref count to synchronize on. Thus, we end-up having two atomic operations per RX packet, on the page refcnt. Where DPDK have zero... By fully taking over the page as an allocator, almost like slab. I can optimize the common case (of the packet-page getting allocated and free'ed on the same CPU), and remove these atomic operations. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>