[PATCH 5/5] vhost/vsock: Allocate nonlinear SKBs for handling large transmit buffers

Will Deacon
2025-06-25T13:16:04Z

When transmitting a vsock packet, virtio_transport_send_pkt_info() calls
virtio_transport_alloc_skb() to allocate and fill SKBs with the transmit
data. Unfortunately, these are always linear allocations and can
therefore result in significant pressure on kmalloc() considering that
the maximum packet size (VIRTIO_VSOCK_MAX_PKT_BUF_SIZE +
VIRTIO_VSOCK_SKB_HEADROOM) is a little over 64KiB, resulting in a 128KiB
allocation for each packet.

Rework the vsock SKB allocation so that, for sizes with page order
greater than PAGE_ALLOC_COSTLY_ORDER, a nonlinear SKB is allocated
instead with the packet header in the SKB and the transmit data in the
fragments.

Signed-off-by: Will Deacon <will@kernel.org>
---
net/vmw_vsock/virtio_transport_common.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 1b5d9896edae..424eb69e84f9 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -109,7 +109,8 @@ static int virtio_transport_fill_skb(struct sk_buff *skb,
return __zerocopy_sg_from_iter(info->msg, NULL, skb,
&info->msg->msg_iter, len, NULL);

- return memcpy_from_msg(skb_put(skb, len), info->msg, len);
+ virtio_vsock_skb_put(skb);
+ return skb_copy_datagram_from_iter(skb, 0, &info->msg->msg_iter, len);
}

static void virtio_transport_init_hdr(struct sk_buff *skb,
@@ -261,7 +262,11 @@ static struct sk_buff *virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *
if (!zcopy)
skb_len += payload_len;

- skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
+ if (skb_len > SKB_WITH_OVERHEAD(PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
+ skb = virtio_vsock_alloc_skb_with_frags(skb_len, GFP_KERNEL);
+ else
+ skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
+
if (!skb)
return NULL;

--
2.50.0.714.g196bf9f422-goog