Messages in this thread | | | Date | Fri, 3 Mar 2023 12:22:21 +0100 | Subject | Re: [PATCH bpf-next v1 1/2] xdp: recycle Page Pool backed skbs built from XDP frames | From | Alexander Lobakin <> |
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From: Yunsheng Lin <linyunsheng@huawei.com> Date: Thu, 2 Mar 2023 10:30:13 +0800
> 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.
[...]
> 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/
And they are fixed :D No drivers currently which use Page Pool mix PP pages with non-PP. And it's impossible to trigger try_coalesce() or so at least on cpumap path since we're only creating skbs at that moment, they don't come from anywhere else.
> > 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.
xdpf_clone() clones a frame to a new full page and doesn't copy its skb_shared_info.
> > 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. > > https://lore.kernel.org/netdev/CANn89iKgZU4Q+THXupzZi4hETuKuCOvOB=iHpp5JzQTNv_Fg_A@mail.gmail.com/
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.
> >> >> /* Allow SKB to reuse area used by xdp_frame */ >> xdp_scrub_frame(xdpf); >>
Thanks, Olek
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