On Wed, Mar 11, 2026 at 2:31 AM Vishwanath Seshagiri <[email protected]> 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 <[email protected]>
> ---
> Changes in v11:
> - add_recvbuf_small: encode alloc_len and xdp_headroom in ctx via
> mergeable_len_to_ctx() so receive_small() recovers the actual buflen
> via mergeable_ctx_to_truesize() (Michael S. Tsirkin)
> - receive_small_build_skb, receive_small_xdp: accept buflen parameter
> instead of recomputing it, to use the actual allocation size
> - v10:
>
> https://lore.kernel.org/virtualization/[email protected]/
>
> Changes in v10:
> - add_recvbuf_small: use alloc_len to avoid clobbering len; v9 feedback
> was about truesize under-accounting, not variable naming — misunderstood
> the comment in v9
> - v9:
>
> https://lore.kernel.org/virtualization/[email protected]/
>
> Changes in v9:
> - Fix virtnet_skb_append_frag() for XSK callers (Michael S. Tsirkin)
> - v8:
>
> https://lore.kernel.org/virtualization/[email protected]/
>
> Changes in v8:
> - Remove virtnet_no_page_pool() helper, replace with direct !rq->page_pool
> checks or inlined conditions (Xuan Zhuo)
> - Extract virtnet_rq_submit() helper to consolidate DMA/non-DMA buffer
> submission in add_recvbuf_small() and add_recvbuf_mergeable()
> - Add skb_mark_for_recycle(nskb) for overflow frag_list skbs in
> virtnet_skb_append_frag() to ensure page_pool pages are returned to
> the pool instead of freed via put_page()
> - Rebase on net-next (kzalloc_objs API)
> - v7:
>
> https://lore.kernel.org/virtualization/[email protected]/
>
> 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/[email protected]/
>
> 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/[email protected]/
>
> 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 | 497 ++++++++++++++++++++-------------------
> 2 files changed, 251 insertions(+), 247 deletions(-)
>
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index 17108c359216..b2fd90466bab 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -452,6 +452,7 @@ 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 72d6a9c6a5a2..a85d75a7f539 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,
> @@ -709,12 +704,10 @@ static struct page *get_a_page(struct receive_queue
> *rq, gfp_t gfp_mask)
> 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 (!rq->page_pool)
> 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);
> }
>
> static void enable_rx_mode_work(struct virtnet_info *vi)
> @@ -876,10 +869,16 @@ static struct sk_buff *page_to_skb(struct virtnet_info
> *vi,
> skb = virtnet_build_skb(buf, truesize, p - buf, len);
> if (unlikely(!skb))
> return NULL;
> + /* Big packets mode chains pages via page->private, which is
> + * incompatible with the way page_pool uses page->private.
> + * Currently, big packets mode doesn't use page pools.
> + */
> + if (!rq->page_pool) {
> + page = (struct page *)page->private;
> + if (page)
> + give_pages(rq, page);
> + }
>
> - page = (struct page *)page->private;
> - if (page)
> - give_pages(rq, page);
> goto ok;
> }
>
> @@ -925,133 +924,16 @@ static struct sk_buff *page_to_skb(struct virtnet_info
> *vi,
> hdr = skb_vnet_common_hdr(skb);
> memcpy(hdr, hdr_p, hdr_len);
> if (page_to_free)
> - put_page(page_to_free);
> + page_pool_put_page(rq->page_pool, page_to_free, -1, true);
>
> return skb;
> }
>
> -static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
> -{
> - struct virtnet_info *vi = rq->vq->vdev->priv;
> - struct page *page = virt_to_head_page(buf);
> - struct virtnet_rq_dma *dma;
> - void *head;
> - int offset;
> -
> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> - head = page_address(page);
> -
> - dma = head;
> -
> - --dma->ref;
> -
> - if (dma->need_sync && len) {
> - offset = buf - (head + sizeof(*dma));
> -
> - virtqueue_map_sync_single_range_for_cpu(rq->vq, dma->addr,
> - offset, len,
> - DMA_FROM_DEVICE);
> - }
> -
> - if (dma->ref)
> - return;
> -
> - virtqueue_unmap_single_attrs(rq->vq, dma->addr, dma->len,
> - DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> - put_page(page);
> -}
> -
> static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void
> **ctx)
> {
> - struct virtnet_info *vi = rq->vq->vdev->priv;
> - void *buf;
> -
> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> + BUG_ON(!rq->page_pool);
>
> - buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> - if (buf)
> - virtnet_rq_unmap(rq, buf, *len);
> -
> - return buf;
> -}
> -
> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32
> len)
> -{
> - struct virtnet_info *vi = rq->vq->vdev->priv;
> - struct virtnet_rq_dma *dma;
> - dma_addr_t addr;
> - u32 offset;
> - void *head;
> -
> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> - head = page_address(rq->alloc_frag.page);
> -
> - offset = buf - head;
> -
> - dma = head;
> -
> - addr = dma->addr - sizeof(*dma) + offset;
> -
> - sg_init_table(rq->sg, 1);
> - sg_fill_dma(rq->sg, addr, len);
> -}
> -
> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> -{
> - struct page_frag *alloc_frag = &rq->alloc_frag;
> - struct virtnet_info *vi = rq->vq->vdev->priv;
> - struct virtnet_rq_dma *dma;
> - void *buf, *head;
> - dma_addr_t addr;
> -
> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> - head = page_address(alloc_frag->page);
> -
> - dma = head;
> -
> - /* new pages */
> - if (!alloc_frag->offset) {
> - if (rq->last_dma) {
> - /* Now, the new page is allocated, the last dma
> - * will not be used. So the dma can be unmapped
> - * if the ref is 0.
> - */
> - virtnet_rq_unmap(rq, rq->last_dma, 0);
> - rq->last_dma = NULL;
> - }
> -
> - dma->len = alloc_frag->size - sizeof(*dma);
> -
> - addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
> - dma->len, DMA_FROM_DEVICE,
> 0);
> - if (virtqueue_map_mapping_error(rq->vq, addr))
> - return NULL;
> -
> - dma->addr = addr;
> - dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
> -
> - /* Add a reference to dma to prevent the entire dma from
> - * being released during error handling. This reference
> - * will be freed after the pages are no longer used.
> - */
> - get_page(alloc_frag->page);
> - dma->ref = 1;
> - alloc_frag->offset = sizeof(*dma);
> -
> - rq->last_dma = dma;
> - }
> -
> - ++dma->ref;
> -
> - buf = head + alloc_frag->offset;
> -
> - get_page(alloc_frag->page);
> - alloc_frag->offset += size;
> -
> - return buf;
> + return virtqueue_get_buf_ctx(rq->vq, len, ctx);
> }
>
> static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> @@ -1067,9 +949,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue
> *vq, void *buf)
> return;
> }
>
> - if (!vi->big_packets || vi->mergeable_rx_bufs)
> - virtnet_rq_unmap(rq, buf, 0);
> -
> virtnet_rq_free_buf(vi, rq, buf);
> }
>
> @@ -1335,7 +1214,7 @@ static int xsk_append_merge_buffer(struct virtnet_info
> *vi,
>
> truesize = len;
>
> - curr_skb = virtnet_skb_append_frag(head_skb, curr_skb, page,
> + curr_skb = virtnet_skb_append_frag(rq, head_skb, curr_skb,
> page,
> buf, len, truesize);
> if (!curr_skb) {
> put_page(page);
> @@ -1771,7 +1650,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> return ret;
> }
>
> -static void put_xdp_frags(struct xdp_buff *xdp)
> +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
> {
> struct skb_shared_info *shinfo;
> struct page *xdp_page;
> @@ -1781,7 +1660,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
> shinfo = xdp_get_shared_info_from_buff(xdp);
> for (i = 0; i < shinfo->nr_frags; i++) {
> xdp_page = skb_frag_page(&shinfo->frags[i]);
> - put_page(xdp_page);
> + page_pool_put_page(rq->page_pool, xdp_page, -1, true);
> }
> }
> }
> @@ -1873,7 +1752,7 @@ static struct page *xdp_linearize_page(struct
> net_device *dev,
> if (page_off + *len + tailroom > PAGE_SIZE)
> return NULL;
>
> - page = alloc_page(GFP_ATOMIC);
> + page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
> if (!page)
> return NULL;
>
> @@ -1896,8 +1775,12 @@ static struct page *xdp_linearize_page(struct
> net_device *dev,
> p = virt_to_head_page(buf);
> off = buf - page_address(p);
>
> + if (rq->use_page_pool_dma)
> + page_pool_dma_sync_for_cpu(rq->page_pool, p,
> + off, buflen);
Intresting, I think we need a patch for -stable to sync for cpu as
well (and probably the XDP_TX path).
> +
> if (check_mergeable_len(dev, ctx, buflen)) {
> - put_page(p);
> + page_pool_put_page(rq->page_pool, p, -1, true);
> goto err_buf;
> }
>
> @@ -1905,38 +1788,36 @@ static struct page *xdp_linearize_page(struct
> net_device *dev,
> * is sending packet larger than the MTU.
> */
> if ((page_off + buflen + tailroom) > PAGE_SIZE) {
> - put_page(p);
> + page_pool_put_page(rq->page_pool, p, -1, true);
> goto err_buf;
> }
>
> memcpy(page_address(page) + page_off,
> page_address(p) + off, buflen);
> page_off += buflen;
> - put_page(p);
> + page_pool_put_page(rq->page_pool, p, -1, true);
> }
>
> /* Headroom does not contribute to packet length */
> *len = page_off - XDP_PACKET_HEADROOM;
> return page;
> err_buf:
> - __free_pages(page, 0);
> + page_pool_put_page(rq->page_pool, page, -1, true);
> return NULL;
> }
>
> static struct sk_buff *receive_small_build_skb(struct virtnet_info *vi,
> unsigned int xdp_headroom,
> void *buf,
> - unsigned int len)
> + unsigned int len,
> + unsigned int buflen)
> {
> unsigned int header_offset;
> unsigned int headroom;
> - unsigned int buflen;
> struct sk_buff *skb;
>
> header_offset = VIRTNET_RX_PAD + xdp_headroom;
> headroom = vi->hdr_len + header_offset;
> - buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
> - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
Any reason for remvoing this?
The rest looks fine.
Thanks
