Messages in this thread | | | From | Jesper Dangaard Brouer <> | Date | Fri, 3 Mar 2023 11:31:35 +0100 | Subject | Re: [PATCH bpf-next v1 1/2] xdp: recycle Page Pool backed skbs built from XDP frames |
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On 02/03/2023 03.30, Yunsheng Lin wrote: > On 2023/3/2 0:03, Alexander Lobakin wrote: >> __xdp_build_skb_from_frame() state(d): >> >> /* Until page_pool get SKB return path, release DMA here */ >> >> Page Pool got skb pages recycling in April 2021, but missed this >> function. >> >> xdp_release_frame() is relevant only for Page Pool backed frames and it >> detaches the page from the corresponding Pool in order to make it >> freeable via page_frag_free(). It can instead just mark the output skb >> as eligible for recycling if the frame is backed by a PP. No change for >> other memory model types (the same condition check as before). >> cpumap redirect and veth on Page Pool drivers now become zero-alloc (or >> almost). >> >> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> >> --- >> net/core/xdp.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/net/core/xdp.c b/net/core/xdp.c >> index 8c92fc553317..a2237cfca8e9 100644 >> --- a/net/core/xdp.c >> +++ b/net/core/xdp.c >> @@ -658,8 +658,8 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf, >> * - RX ring dev queue index (skb_record_rx_queue) >> */ >> >> - /* Until page_pool get SKB return path, release DMA here */ >> - xdp_release_frame(xdpf); >> + if (xdpf->mem.type == MEM_TYPE_PAGE_POOL) >> + skb_mark_for_recycle(skb); > > > We both rely on both skb->pp_recycle and page->pp_magic to decide > the page is really from page pool. So there was a few corner case > problem when we are sharing a page for different skb in the driver > level or calling skb_clone() or skb_try_coalesce(). > see: > https://github.com/torvalds/linux/commit/2cc3aeb5ecccec0d266813172fcd82b4b5fa5803 > https://lore.kernel.org/netdev/MW5PR15MB51214C0513DB08A3607FBC1FBDE19@MW5PR15MB5121.namprd15.prod.outlook.com/t/ > https://lore.kernel.org/netdev/167475990764.1934330.11960904198087757911.stgit@localhost.localdomain/ > > As the 'struct xdp_frame' also use 'struct skb_shared_info' which is > sharable, see xdp_get_shared_info_from_frame(). > > For now xdpf_clone() does not seems to handling frag page yet, > so it should be fine for now. > > IMHO we should find a way to use per-page marker, instead of both > per-skb and per-page markers, in order to avoid the above problem > for xdp if xdp has a similar processing as skb, as suggested by Eric. >
Moving to a per-page marker can be *more* expensive if the struct-page memory isn't cache-hot. So, if struct-page is accessed anyhow then sure we can move it to a per-page marker.
> https://lore.kernel.org/netdev/CANn89iKgZU4Q+THXupzZi4hETuKuCOvOB=iHpp5JzQTNv_Fg_A@mail.gmail.com/ > >> >> /* Allow SKB to reuse area used by xdp_frame */ >> xdp_scrub_frame(xdpf); >> >
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