Re: [PATCH net-next v10] virtio_net: add page_pool support for buffer allocation
From: Paolo Abeni <pabeni@redhat.com>
Date: 2026-03-05 12:03:41
Also in:
lkml, virtualization
On 3/3/26 8:42 AM, Vishwanath Seshagiri wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- Changes in v10: - add_recvbuf_small: use alloc_len to avoid clobbering len (Michael S. Tsirkin) - v9: https://lore.kernel.org/virtualization/20260302041005.1627210-1-vishs@meta.com/ (local) Changes in v9: - Fix virtnet_skb_append_frag() for XSK callers (Michael S. Tsirkin) - v8: https://lore.kernel.org/virtualization/e824c5a3-cfe0-4d11-958f-c3ec82d11d37@meta.com/ (local) 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/20260210014305.3236342-1-vishs@meta.com/ (local) 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/ (local) 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/ (local) 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 | 466 ++++++++++++++++++++------------------- 2 files changed, 237 insertions(+), 230 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..d722031604bf 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); - - 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; + BUG_ON(!rq->page_pool); - 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); + if (check_mergeable_len(dev, ctx, buflen)) { - put_page(p); + page_pool_put_page(rq->page_pool, p, -1, true); goto err_buf; }@@ -1905,21 +1788,21 @@ 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; }@@ -1996,7 +1879,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev, goto err_xdp; buf = page_address(xdp_page); - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); page = xdp_page; }@@ -2028,13 +1911,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev, if (metasize) skb_metadata_set(skb, metasize); + skb_mark_for_recycle(skb); + return skb; err_xdp: u64_stats_inc(&stats->xdp_drops); err: u64_stats_inc(&stats->drops); - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); xdp_xmit: return NULL; }@@ -2056,6 +1941,13 @@ static struct sk_buff *receive_small(struct net_device *dev, */ buf -= VIRTNET_RX_PAD + xdp_headroom; + if (rq->use_page_pool_dma) { + int offset = buf - page_address(page) + + VIRTNET_RX_PAD + xdp_headroom; + + page_pool_dma_sync_for_cpu(rq->page_pool, page, offset, len); + } + len -= vi->hdr_len; u64_stats_add(&stats->bytes, len);@@ -2082,12 +1974,14 @@ static struct sk_buff *receive_small(struct net_device *dev, } skb = receive_small_build_skb(vi, xdp_headroom, buf, len); - if (likely(skb)) + if (likely(skb)) { + skb_mark_for_recycle(skb); return skb; + } err: u64_stats_inc(&stats->drops); - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); return NULL; }@@ -2142,7 +2036,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf, } u64_stats_add(&stats->bytes, len); page = virt_to_head_page(buf); - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); } }@@ -2252,8 +2146,12 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev, page = virt_to_head_page(buf); offset = buf - page_address(page); + if (rq->use_page_pool_dma) + page_pool_dma_sync_for_cpu(rq->page_pool, page, + offset, len); + if (check_mergeable_len(dev, ctx, len)) { - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); goto err; }@@ -2272,7 +2170,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev, return 0; err: - put_xdp_frags(xdp); + put_xdp_frags(rq, xdp); return -EINVAL; }@@ -2337,7 +2235,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi, if (*len + xdp_room > PAGE_SIZE) return NULL; - xdp_page = alloc_page(GFP_ATOMIC); + xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC); if (!xdp_page) return NULL;@@ -2347,7 +2245,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi, *frame_sz = PAGE_SIZE; - put_page(*page); + page_pool_put_page(rq->page_pool, *page, -1, true); *page = xdp_page;@@ -2393,6 +2291,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev, head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz); if (unlikely(!head_skb)) break; + + skb_mark_for_recycle(head_skb); return head_skb; case XDP_TX:@@ -2403,10 +2303,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev, break; } - put_xdp_frags(&xdp); + put_xdp_frags(rq, &xdp); err_xdp: - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); mergeable_buf_free(rq, num_buf, dev, stats); u64_stats_inc(&stats->xdp_drops);@@ -2414,7 +2314,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev, return NULL; } -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)@@ -2429,6 +2330,9 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb, if (unlikely(!nskb)) return NULL; + if (head_skb->pp_recycle) + skb_mark_for_recycle(nskb); + if (curr_skb == head_skb) skb_shinfo(curr_skb)->frag_list = nskb; else@@ -2446,7 +2350,10 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb, offset = buf - page_address(page); if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) { - put_page(page); + if (head_skb->pp_recycle) + page_pool_put_page(rq->page_pool, page, -1, true); + else + put_page(page); skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1, len, truesize); } else {@@ -2475,6 +2382,10 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, unsigned int headroom = mergeable_ctx_to_headroom(ctx); head_skb = NULL; + + if (rq->use_page_pool_dma) + page_pool_dma_sync_for_cpu(rq->page_pool, page, offset, len); + u64_stats_add(&stats->bytes, len - vi->hdr_len); if (check_mergeable_len(dev, ctx, len))@@ -2499,6 +2410,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, if (unlikely(!curr_skb)) goto err_skb; + + skb_mark_for_recycle(head_skb); while (--num_buf) { buf = virtnet_rq_get_buf(rq, &len, &ctx); if (unlikely(!buf)) {@@ -2513,11 +2426,17 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, u64_stats_add(&stats->bytes, len); page = virt_to_head_page(buf); + if (rq->use_page_pool_dma) { + offset = buf - page_address(page); + page_pool_dma_sync_for_cpu(rq->page_pool, page, + offset, len); + } + if (check_mergeable_len(dev, ctx, len)) goto err_skb; truesize = mergeable_ctx_to_truesize(ctx); - 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) goto err_skb;@@ -2527,7 +2446,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, return head_skb; err_skb: - put_page(page); + page_pool_put_page(rq->page_pool, page, -1, true); mergeable_buf_free(rq, num_buf, dev, stats); err_buf:@@ -2658,6 +2577,24 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq, virtnet_receive_done(vi, rq, skb, flags); } +static int virtnet_rq_submit(struct receive_queue *rq, char *buf, + int len, void *ctx, gfp_t gfp) +{ + if (rq->use_page_pool_dma) { + struct page *page = virt_to_head_page(buf); + dma_addr_t addr = page_pool_get_dma_addr(page) + + (buf - (char *)page_address(page)); + + sg_init_table(rq->sg, 1); + sg_fill_dma(rq->sg, addr, len); + return virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, + buf, ctx, gfp); + } + + sg_init_one(rq->sg, buf, len); + return virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp); +} + /* Unlike mergeable buffers, all buffers are allocated to the * same size, except for the headroom. For this reason we do * not need to use mergeable_len_to_ctx here - it is enough@@ -2666,32 +2603,27 @@ 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; + unsigned int alloc_len; + 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); + alloc_len = len; + buf = page_pool_alloc_va(rq->page_pool, &alloc_len, gfp); if (unlikely(!buf)) return -ENOMEM;
As noted by Micheal in the previous revision the above will skb->truesize under accounting. That is not safe and at least need a solid explaination, which is still missing. /P