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

[Vishwanath Seshagiri <vishs@meta.com>]

On 2/25/26 2:03 PM, Xuan Zhuo wrote:
> On Tue, 24 Feb 2026 20:49:10 -0800, Vishwanath Seshagiri <vishs@meta.com> 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@meta.com>
>> ---
>> Resend for net-next window (no changes from v7).
>> - v7:
>>    https://lore.kernel.org/virtualization/20260210014305.3236342-1-vishs@meta.com/
>>
>> 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@meta.com/
>>
>> 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@meta.com/
>>
>> 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.