On Thu, 23 May 2019 21:20:35 +0300Thank for what you do, it can simplify a lot...
Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:
Add XDP support based on rx page_pool allocator, one frame per page.
Page pool allocator is used with assumption that only one rx_handler
is running simultaneously. DMA map/unmap is reused from page pool
despite there is no need to map whole page.
When using page_pool for DMA-mapping, your XDP-memory model must use
1-page per packet, which you state you do. This is because
__page_pool_put_page() fallback mode does a __page_pool_clean_page()
unmapping the DMA. Ilias and I are looking at options for removing this
restriction as Mlx5 would need it (when we extend the SKB to return
pages to page_pool).
Unfortunately, I've found another blocker for drivers using the DMA
mapping feature of page_pool. We don't properly handle the case, where
a remote TX-driver have xdp_frame's in-flight, and simultaneously the
sending driver is unloaded and take down the page_pool. Nothing crash,
but we end-up calling put_page() on a page that is still DMA-mapped.
Hope there will be no changes in page_pool API.
I'm working on different solutions for fixing this, see here:
-- Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat