net: xdp: add xdp_update_skb_shared_info utility routine

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 frags 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 non-linear xdp_frame to a skb after performing a XDP_REDIRECT.

Acked-by: Toke Hoiland-Jorgensen <toke@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/bfd23fb8a8d7438724f7819c567cdf99ffd6226f.1642758637.git.lorenzo@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 485e949..1f8641e 100644 (file)
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -67,7 +67,10 @@ struct xdp_txq_info {
 };
 
 enum xdp_buff_flags {
-       XDP_FLAGS_HAS_FRAGS     = BIT(0), /* non-linear xdp buff */
+       XDP_FLAGS_HAS_FRAGS             = BIT(0), /* non-linear xdp buff */
+       XDP_FLAGS_FRAGS_PF_MEMALLOC     = BIT(1), /* xdp paged memory is under
+                                                  * pressure
+                                                  */
 };
 
 struct xdp_buff {
@@ -96,6 +99,16 @@ static __always_inline void xdp_buff_clear_frags_flag(struct xdp_buff *xdp)
        xdp->flags &= ~XDP_FLAGS_HAS_FRAGS;
 }
 
+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_has_frags(struct xdp_frame *frame)
        return !!(frame->flags & XDP_FLAGS_HAS_FRAGS);
 }
 
+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;
+}
+
 /* 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 7aba355..9e469f5 100644 (file)
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -561,8 +561,14 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
                                           struct sk_buff *skb,
                                           struct net_device *dev)
 {
+       struct skb_shared_info *sinfo = xdp_get_shared_info_from_frame(xdpf);
        unsigned int headroom, frame_size;
        void *hard_start;
+       u8 nr_frags;
+
+       /* xdp frags frame */
+       if (unlikely(xdp_frame_has_frags(xdpf)))
+               nr_frags = sinfo->nr_frags;
 
        /* Part of headroom was reserved to xdpf */
        headroom = sizeof(*xdpf) + xdpf->headroom;
@@ -582,6 +588,12 @@ 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_has_frags(xdpf)))
+               xdp_update_skb_shared_info(skb, nr_frags,
+                                          sinfo->xdp_frags_size,
+                                          nr_frags * xdpf->frame_sz,
+                                          xdp_frame_is_frag_pfmemalloc(xdpf));
+
        /* Essential SKB info: protocol and skb->dev */
        skb->protocol = eth_type_trans(skb, dev);