Commit 03a92f03 authored by Will Deacon's avatar Will Deacon Committed by Michael S. Tsirkin
Browse files

vsock/virtio: Resize receive buffers so that each SKB fits in a 4K page 



When allocating receive buffers for the vsock virtio RX virtqueue, an
SKB is allocated with a 4140 data payload (the 44-byte packet header +
VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE). Even when factoring in the SKB
overhead, the resulting 8KiB allocation thanks to the rounding in
kmalloc_reserve() is wasteful (~3700 unusable bytes) and results in a
higher-order page allocation on systems with 4KiB pages just for the
sake of a few hundred bytes of packet data.

Limit the vsock virtio RX buffers to 4KiB per SKB, resulting in much
better memory utilisation and removing the need to allocate higher-order
pages entirely.

Reviewed-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
Message-Id: <20250717090116.11987-5-will@kernel.org>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 87dbae5e

include/linux/virtio_vsock.h

+6 −1
Original line number Diff line number Diff line
@@ -106,7 +106,12 @@ static inline size_t virtio_vsock_skb_len(struct sk_buff *skb) 
	return (size_t)(skb_end_pointer(skb) - skb->head);

}



#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)

/* Dimension the RX SKB so that the entire thing fits exactly into

 * a single 4KiB page. This avoids wasting memory due to alloc_skb()

 * rounding up to the next page order and also means that we

 * don't leave higher-order pages sitting around in the RX queue.

 */

#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	SKB_WITH_OVERHEAD(1024 * 4)

#define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL

#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)

net/vmw_vsock/virtio_transport.c

+1 −1
Original line number Diff line number Diff line
@@ -307,7 +307,7 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk) 


static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)

{

	int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM;

	int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;

	struct scatterlist pkt, *p;

	struct virtqueue *vq;

	struct sk_buff *skb;