On Thu, Dec 21, 2023 at 10:42 PM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: > > On 2023/12/22 5:22, Mina Almasry wrote: > > On Thu, Dec 21, 2023 at 3:32 AM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: > >> > >> On 2023/12/20 11:01, Mina Almasry wrote: > >> > >> ... > >> > >>>>>> Perhaps we should aim to not export netmem_to_page(), > >>>>>> prevent modules from accessing it directly. > >>>>> > >>>>> +1. > >>>> > >>> > >>> I looked into this, but it turns out it's a slightly bigger change > >>> that needs some refactoring to make it work. There are few places > >>> where I believe I need to add netmem_to_page() that are exposed to the > >>> drivers via inline helpers, these are: > >>> > >>> - skb_frag_page(), which returns NULL if the netmem is not a page, but > >>> needs to do a netmem_to_page() to return the page otherwise. > >> > >> Is it possible to introduce something like skb_frag_netmem() for > >> netmem? so that we can keep most existing users of skb_frag_page() > >> unchanged and avoid adding additional checking overhead for existing > >> users. > >> > > > > In my experience most current skb_frag_page() users need specifically > > the struct page*. Example is illegal_highdma() which > > PageHighMem(skb_frag_page()) > > For illegal_highdma() case, is it possible to use something like > skb_readabe_frag() checking to avoid calling skb_frag_page() for netmem? > Not teh skb_readable_frag() check I think, because illegal_highdma() is not trying to read the SKB per se. But I agree with your general point, and that should be handled correctly in this patch which adds devmem support: https://patchwork.kernel.org/project/netdevbpf/patch/20231218024024.3516870-10-almasrymina@xxxxxxxxxx/ The idea being that skb_frag_page() can return NULL if the frag is not paged, and the relevant callers are modified to handle that. > > > > But RFC v5 adds skb_frag_netmem() for callsites that want a netmem and > > don't care about specifically a page: > > > > https://patchwork.kernel.org/project/netdevbpf/patch/20231218024024.3516870-10-almasrymina@xxxxxxxxxx/ > > > >>> - The helpers inside skb_add_rx_frag(), which needs to do a > >>> netmem_to_page() to set skb->pfmemalloc. > >> > >> Similar as above, perhaps introduce something like skb_add_rx_netmem_frag()? > >> > > > > Yes, v3 of this series adds skb_add_rx_frag_netmem(): > > > > https://patchwork.kernel.org/project/netdevbpf/patch/20231220214505.2303297-4-almasrymina@xxxxxxxxxx/ -- Thanks, Mina
