On 2023/3/3 21:26, Alexander Lobakin wrote: > From: Yunsheng Lin <linyunsheng@xxxxxxxxxx> > Date: Fri, 3 Mar 2023 20:44:24 +0800 > >> On 2023/3/3 19:22, Alexander Lobakin wrote: >>> From: Yunsheng Lin <linyunsheng@xxxxxxxxxx> >>> Date: Thu, 2 Mar 2023 10:30:13 +0800 > > [...] > >>> And they are fixed :D >>> No drivers currently which use Page Pool mix PP pages with non-PP. And >> >> The wireless adapter which use Page Pool *does* mix PP pages with >> non-PP, see below discussion: >> >> https://lore.kernel.org/netdev/156f3e120bd0757133cb6bc11b76889637b5e0a6.camel@xxxxxxxxx/ > > Ah right, I remember that (also was fixed). > Not that I think it is correct to mix them -- for my PoV, a driver > shoule either give *all* its Rx buffers as PP-backed or not use PP at all. > > [...] > >>> As Jesper already pointed out, not having a quick way to check whether >>> we have to check ::pp_magic at all can decrease performance. So it's >>> rather a shortcut. >> >> When we are freeing a page by updating the _refcount, I think >> we are already touching the cache of ::pp_magic. > > But no page freeing happens before checking for skb->pp_recycle, neither > in skb_pp_recycle() (skb_free_head() etc.)[0] nor in skb_frag_unref()[1]. If we move to per page marker, we probably do not need checking skb->pp_recycle. Note both page_pool_return_skb_page() and skb_free_frag() can reuse the cache line triggered by per page marker checking if the per page marker is in the 'struct page'. > >> >> Anyway, I am not sure checking ::pp_magic is correct when a >> page will be passing between different subsystem and back to >> the network stack eventually, checking ::pp_magic may not be >> correct if this happens. >> >> Another way is to use the bottom two bits in bv_page, see: >> https://www.spinics.net/lists/netdev/msg874099.html >> >>> >>>> >>>>> >>>>> /* Allow SKB to reuse area used by xdp_frame */ >>>>> xdp_scrub_frame(xdpf); >>>>> >>> >>> Thanks, >>> Olek >>> . >>> > > [0] https://elixir.bootlin.com/linux/latest/source/net/core/skbuff.c#L808 > [1] > https://elixir.bootlin.com/linux/latest/source/include/linux/skbuff.h#L3385 > > Thanks, > Olek > . >
