netdev - RE: [PATCH v12 bpf-next 05/18] net: xdp: add xdp_update_skb_shared

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Date:   Tue, 31 Aug 2021 16:38:52 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, shayagr@...zon.com,
        john.fastabend@...il.com, dsahern@...nel.org, brouer@...hat.com,
        echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        tirthendu.sarkar@...el.com, toke@...hat.com
Subject: RE: [PATCH v12 bpf-next 05/18] net: xdp: add
 xdp_update_skb_shared_info utility routine

Lorenzo Bianconi wrote:
> Introduce xdp_update_skb_shared_info routine to update frags array
> metadata in skb_shared_info data structure converting to a skb from
> a xdp_buff or xdp_frame.
> According to the current skb_shared_info architecture in
> xdp_frame/xdp_buff and to the xdp multi-buff support, there is
> no need to run skb_add_rx_frag() and reset frags array converting the buffer
> to a skb since the frag array will be in the same position for xdp_buff/xdp_frame
> and for the skb, we just need to update memory metadata.
> Introduce XDP_FLAGS_PF_MEMALLOC flag in xdp_buff_flags in order to mark
> the xdp_buff or xdp_frame as under memory-pressure if pages of the frags array
> are under memory pressure. Doing so we can avoid looping over all fragments in
> xdp_update_skb_shared_info routine. The driver is expected to set the
> flag constructing the xdp_buffer using xdp_buff_set_frag_pfmemalloc
> utility routine.
> Rely on xdp_update_skb_shared_info in __xdp_build_skb_from_frame routine
> converting the multi-buff xdp_frame to a skb after performing a XDP_REDIRECT.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>

Acked-by: John Fastabend <john.fastabend@...il.com>