Re: [PATCH v7 RESEND net-next] virtio_net: add page_pool support for buffer allocation

[Vishwanath Seshagiri]

On 2/25/26 2:03 PM, Xuan Zhuo wrote:
> On Tue, 24 Feb 2026 20:49:10 -0800, Vishwanath Seshagiri <vishs@xxxxxxxx> wrote:
> > Use page_pool for RX buffer allocation in mergeable and small buffer
> > modes to enable page recycling and avoid repeated page allocator calls.
> > skb_mark_for_recycle() enables page reuse in the network stack.
> >
> > Big packets mode is unchanged because it uses page->private for linked
> > list chaining of multiple pages per buffer, which conflicts with
> > page_pool's internal use of page->private.
> >
> > Implement conditional DMA premapping using virtqueue_dma_dev():
> > - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
> >    handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
> > - When NULL (VDUSE, direct physical): page_pool handles allocation only,
> >    submit via virtqueue_add_inbuf_ctx()
> >
> > This preserves the DMA premapping optimization from commit 31f3cd4e5756b
> > ("virtio-net: rq submits premapped per-buffer") while adding page_pool
> > support as a prerequisite for future zero-copy features (devmem TCP,
> > io_uring ZCRX).
> >
> > Page pools are created in probe and destroyed in remove (not open/close),
> > following existing driver behavior where RX buffers remain in virtqueues
> > across interface state changes.
> >
> > Signed-off-by: Vishwanath Seshagiri <vishs@xxxxxxxx>
> > ---
> > Resend for net-next window (no changes from v7).
> > - v7:
> >    https://lore.kernel.org/virtualization/20260210014305.3236342-1-vishs@xxxxxxxx/
> >
> > Changes in v7:
> > - Replace virtnet_put_page() helper with direct page_pool_put_page()
> >    calls (Xuan Zhuo)
> > - Add virtnet_no_page_pool() helper to consolidate big_packets mode check
> >    (Michael S. Tsirkin)
> > - Add DMA sync_for_cpu for subsequent buffers in xdp_linearize_page() when
> >    use_page_pool_dma is set (Michael S. Tsirkin)
> > - Remove unused pp_params.dev assignment in non-DMA path
> > - Add page pool recreation in virtnet_restore_up() for freeze/restore support (Chris Mason's
> > Review Prompt)
> > - v6:
> >    https://lore.kernel.org/virtualization/20260208175410.1910001-1-vishs@xxxxxxxx/
> >
> > Changes in v6:
> > - Drop page_pool_frag_offset_add() helper and switch to page_pool_alloc_va();
> >    page_pool_alloc_netmem() already handles internal fragmentation internally
> >    (Jakub Kicinski)
> > - v5:
> >    https://lore.kernel.org/virtualization/20260206002715.1885869-1-vishs@xxxxxxxx/
> >
> > Benchmark results:
> >
> > Configuration: pktgen TX -> tap -> vhost-net | virtio-net RX -> XDP_DROP
> >
> > Small packets (64 bytes, mrg_rxbuf=off):
> >    1Q:  853,493 -> 868,923 pps  (+1.8%)
> >    2Q: 1,655,793 -> 1,696,707 pps (+2.5%)
> >    4Q: 3,143,375 -> 3,302,511 pps (+5.1%)
> >    8Q: 6,082,590 -> 6,156,894 pps (+1.2%)
> >
> > Mergeable RX (64 bytes):
> >    1Q:   766,168 ->   814,493 pps  (+6.3%)
> >    2Q: 1,384,871 -> 1,670,639 pps (+20.6%)
> >    4Q: 2,773,081 -> 3,080,574 pps (+11.1%)
> >    8Q: 5,600,615 -> 6,043,891 pps  (+7.9%)
> >
> > Mergeable RX (1500 bytes):
> >    1Q:   741,579 ->   785,442 pps  (+5.9%)
> >    2Q: 1,310,043 -> 1,534,554 pps (+17.1%)
> >    4Q: 2,748,700 -> 2,890,582 pps  (+5.2%)
> >    8Q: 5,348,589 -> 5,618,664 pps  (+5.0%)
> >
> >   drivers/net/Kconfig      |   1 +
> >   drivers/net/virtio_net.c | 467 ++++++++++++++++++++-------------------
> >   2 files changed, 243 insertions(+), 225 deletions(-)
> >
> > diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> > index ac12eaf11755..f1e6b6b0a86f 100644
> > --- a/drivers/net/Kconfig
> > +++ b/drivers/net/Kconfig
> > @@ -450,6 +450,7 @@ config VIRTIO_NET
> >   	depends on VIRTIO
> >   	select NET_FAILOVER
> >   	select DIMLIB
> > +	select PAGE_POOL
> >   	help
> >   	  This is the virtual network driver for virtio.  It can be used with
> >   	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index db88dcaefb20..32aede2b1ed5 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -26,6 +26,7 @@
> >   #include <net/netdev_rx_queue.h>
> >   #include <net/netdev_queues.h>
> >   #include <net/xdp_sock_drv.h>
> > +#include <net/page_pool/helpers.h>
> >
> >   static int napi_weight = NAPI_POLL_WEIGHT;
> >   module_param(napi_weight, int, 0444);
> > @@ -290,14 +291,6 @@ struct virtnet_interrupt_coalesce {
> >   	u32 max_usecs;
> >   };
> >
> > -/* The dma information of pages allocated at a time. */
> > -struct virtnet_rq_dma {
> > -	dma_addr_t addr;
> > -	u32 ref;
> > -	u16 len;
> > -	u16 need_sync;
> > -};
> > -
> >   /* Internal representation of a send virtqueue */
> >   struct send_queue {
> >   	/* Virtqueue associated with this send _queue */
> > @@ -356,8 +349,10 @@ struct receive_queue {
> >   	/* Average packet length for mergeable receive buffers. */
> >   	struct ewma_pkt_len mrg_avg_pkt_len;
> >
> > -	/* Page frag for packet buffer allocation. */
> > -	struct page_frag alloc_frag;
> > +	struct page_pool *page_pool;
> > +
> > +	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
> > +	bool use_page_pool_dma;
> >
> >   	/* RX: fragments + linear part + virtio header */
> >   	struct scatterlist sg[MAX_SKB_FRAGS + 2];
> > @@ -370,9 +365,6 @@ struct receive_queue {
> >
> >   	struct xdp_rxq_info xdp_rxq;
> >
> > -	/* Record the last dma info to free after new pages is allocated. */
> > -	struct virtnet_rq_dma *last_dma;
> > -
> >   	struct xsk_buff_pool *xsk_pool;
> >
> >   	/* xdp rxq used by xsk */
> > @@ -521,11 +513,14 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> >   			       struct virtnet_rq_stats *stats);
> >   static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
> >   				 struct sk_buff *skb, u8 flags);
> > -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
> > +					       struct sk_buff *head_skb,
> >   					       struct sk_buff *curr_skb,
> >   					       struct page *page, void *buf,
> >   					       int len, int truesize);
> >   static void virtnet_xsk_completed(struct send_queue *sq, int num);
> > +static void free_unused_bufs(struct virtnet_info *vi);
> > +static void virtnet_del_vqs(struct virtnet_info *vi);
> >
> >   enum virtnet_xmit_type {
> >   	VIRTNET_XMIT_TYPE_SKB,
> > @@ -706,15 +701,18 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> >   	return p;
> >   }
> >
> > +static bool virtnet_no_page_pool(struct virtnet_info *vi)
> > +{
>
> Can we check vi->page_pool?
>
> In virtnet_create_page_pools, we can check
> "vi->big_packets && !vi->mergeable_rx_bufs" directly.
>
> Then other calls will be more efficient.

Ack. Will make this change.

> > +	return vi->big_packets && !vi->mergeable_rx_bufs;
> > +}
> > +
> >   static void virtnet_rq_free_buf(struct virtnet_info *vi,
> >   				struct receive_queue *rq, void *buf)
> >   {
> > -	if (vi->mergeable_rx_bufs)
> > -		put_page(virt_to_head_page(buf));
> > -	else if (vi->big_packets)
> > +	if (virtnet_no_page_pool(vi))
> >   		give_pages(rq, buf);
> >   	else
> > -		put_page(virt_to_head_page(buf));
> > +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf), -1, false);
> >   }
>
>
> [...]
>
>
> >   err_buf:
> > @@ -2666,32 +2586,40 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> >   static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> >   			     gfp_t gfp)
> >   {
> > -	char *buf;
> >   	unsigned int xdp_headroom = virtnet_get_headroom(vi);
> >   	void *ctx = (void *)(unsigned long)xdp_headroom;
> > -	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
> > +	unsigned int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
> > +	struct page *page;
> > +	dma_addr_t addr;
> > +	char *buf;
> >   	int err;
> >
> >   	len = SKB_DATA_ALIGN(len) +
> >   	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> >
> > -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> > -		return -ENOMEM;
> > -
> > -	buf = virtnet_rq_alloc(rq, len, gfp);
> > +	buf = page_pool_alloc_va(rq->page_pool, &len, gfp);
> >   	if (unlikely(!buf))
> >   		return -ENOMEM;
> >
> >   	buf += VIRTNET_RX_PAD + xdp_headroom;
> >
> > -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
> > +	if (rq->use_page_pool_dma) {
> > +		page = virt_to_head_page(buf);
> > +		addr = page_pool_get_dma_addr(page) +
> > +		       (buf - (char *)page_address(page));
> >
> > -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > -	if (err < 0) {
> > -		virtnet_rq_unmap(rq, buf, 0);
> > -		put_page(virt_to_head_page(buf));
> > +		sg_init_table(rq->sg, 1);
> > +		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
> > +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
> > +						    buf, ctx, gfp);
> > +	} else {
> > +		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
> > +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
> > +					      buf, ctx, gfp);
> >   	}
>
> Maybe we should introduce a helper to do this, as the merge mode needs this
> too.

Ack. I will add a helper here.

> Thanks.