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Message-ID: <29fc47da-f9b3-9698-d58d-a06010945a21@redhat.com>
Date: Tue, 7 Sep 2021 15:40:20 +0200
From: Jesper Dangaard Brouer <jbrouer@...hat.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
netdev@...r.kernel.org
Cc: brouer@...hat.com, 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, 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 v13 bpf-next 05/18] net: xdp: add
xdp_update_skb_shared_info utility routine
On 07/09/2021 14.35, 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.
>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
> include/net/xdp.h | 33 ++++++++++++++++++++++++++++++++-
> net/core/xdp.c | 17 +++++++++++++++++
> 2 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index ed5ea784fd45..53cccdc9528c 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -67,7 +67,10 @@ struct xdp_txq_info {
> };
>
> enum xdp_buff_flags {
> - XDP_FLAGS_MULTI_BUFF = BIT(0), /* non-linear xdp buff */
> + XDP_FLAGS_MULTI_BUFF = BIT(0), /* non-linear xdp buff */
> + XDP_FLAGS_FRAGS_PF_MEMALLOC = BIT(1), /* xdp multi-buff paged memory
> + * is under pressure
> + */
> };
>
> struct xdp_buff {
> @@ -96,6 +99,16 @@ static __always_inline void xdp_buff_clear_mb(struct xdp_buff *xdp)
> xdp->flags &= ~XDP_FLAGS_MULTI_BUFF;
> }
>
> +static __always_inline bool xdp_buff_is_frag_pfmemalloc(struct xdp_buff *xdp)
> +{
> + return !!(xdp->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
> +}
> +
> +static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
> +{
> + xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
> +}
> +
> static __always_inline void
> xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
> {
> @@ -151,6 +164,11 @@ static __always_inline bool xdp_frame_is_mb(struct xdp_frame *frame)
> return !!(frame->flags & XDP_FLAGS_MULTI_BUFF);
> }
>
> +static __always_inline bool xdp_frame_is_frag_pfmemalloc(struct xdp_frame *frame)
> +{
> + return !!(frame->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
> +}
> +
> #define XDP_BULK_QUEUE_SIZE 16
> struct xdp_frame_bulk {
> int count;
> @@ -186,6 +204,19 @@ static inline void xdp_scrub_frame(struct xdp_frame *frame)
> frame->dev_rx = NULL;
> }
>
> +static inline void
> +xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
> + unsigned int size, unsigned int truesize,
> + bool pfmemalloc)
> +{
> + skb_shinfo(skb)->nr_frags = nr_frags;
> +
> + skb->len += size;
> + skb->data_len += size;
> + skb->truesize += truesize;
> + skb->pfmemalloc |= pfmemalloc;
Do we need to clear gso_type here as it is shared/union with
xdp_frags_size ?
(see below ... it is already cleared before call)
> +}
> +
> /* Avoids inlining WARN macro in fast-path */
> void xdp_warn(const char *msg, const char *func, const int line);
> #define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__)
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index cc92ccb38432..504be3ce3ca9 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -531,8 +531,20 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
> struct sk_buff *skb,
> struct net_device *dev)
> {
> + unsigned int frag_size, frag_tsize;
> unsigned int headroom, frame_size;
> void *hard_start;
> + u8 nr_frags;
> +
> + /* xdp multi-buff frame */
> + if (unlikely(xdp_frame_is_mb(xdpf))) {
> + struct skb_shared_info *sinfo;
> +
> + sinfo = xdp_get_shared_info_from_frame(xdpf);
> + frag_tsize = sinfo->xdp_frags_tsize;
> + frag_size = sinfo->xdp_frags_size;
> + nr_frags = sinfo->nr_frags;
> + }
>
> /* Part of headroom was reserved to xdpf */
> headroom = sizeof(*xdpf) + xdpf->headroom;
> @@ -552,6 +564,11 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
> if (xdpf->metasize)
> skb_metadata_set(skb, xdpf->metasize);
>
> + if (unlikely(xdp_frame_is_mb(xdpf)))
> + xdp_update_skb_shared_info(skb, nr_frags,
> + frag_size, frag_tsize,
> + xdp_frame_is_frag_pfmemalloc(xdpf));
> +
There is a build_skb_around() call before this call, which via
__build_skb_around() will clear top part of skb_shared_info.
(Thus, clearing gso_type not needed ... see above)
> /* Essential SKB info: protocol and skb->dev */
> skb->protocol = eth_type_trans(skb, dev);
>
Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
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