Re: [PATCH v2 1/8] vsock/virtio: limit the memory used per-socket

Jason Wang
2019-05-13T09:59:08Z

On 2019/5/10 下午8:58, Stefano Garzarella wrote:
> Since virtio-vsock was introduced, the buffers filled by the host
> and pushed to the guest using the vring, are directly queued in
> a per-socket list avoiding to copy it.
> These buffers are preallocated by the guest with a fixed
> size (4 KB).
>
> The maximum amount of memory used by each socket should be
> controlled by the credit mechanism.
> The default credit available per-socket is 256 KB, but if we use
> only 1 byte per packet, the guest can queue up to 262144 of 4 KB
> buffers, using up to 1 GB of memory per-socket. In addition, the
> guest will continue to fill the vring with new 4 KB free buffers
> to avoid starvation of other sockets.
>
> This patch solves this issue copying the payload in a new buffer.
> Then it is queued in the per-socket list, and the 4KB buffer used
> by the host is freed.
>
> In this way, the memory used by each socket respects the credit
> available, and we still avoid starvation, paying the cost of an
> extra memory copy. When the buffer is completely full we do a
> "zero-copy", moving the buffer directly in the per-socket list.

I wonder in the long run we should use generic socket accouting
mechanism provided by kernel (e.g socket, skb, sndbuf, recvbug,
truesize) instead of vsock specific thing to avoid duplicating efforts.

>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> drivers/vhost/vsock.c | 2 +
> include/linux/virtio_vsock.h | 8 +++
> net/vmw_vsock/virtio_transport.c | 1 +
> net/vmw_vsock/virtio_transport_common.c | 95 ++++++++++++++++++-------
> 4 files changed, 81 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index bb5fc0e9fbc2..7964e2daee09 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -320,6 +320,8 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
> return NULL;
> }
>
> + pkt->buf_len = pkt->len;
> +
> nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
> if (nbytes != pkt->len) {
> vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index e223e2632edd..345f04ee9193 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -54,9 +54,17 @@ struct virtio_vsock_pkt {
> void *buf;
> u32 len;
> u32 off;
> + u32 buf_len;
> bool reply;
> };
>
> +struct virtio_vsock_buf {
> + struct list_head list;
> + void *addr;
> + u32 len;
> + u32 off;
> +};
> +
> struct virtio_vsock_pkt_info {
> u32 remote_cid, remote_port;
> struct vsock_sock *vsk;
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 15eb5d3d4750..af1d2ce12f54 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -280,6 +280,7 @@ static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
> break;
> }
>
> + pkt->buf_len = buf_len;
> pkt->len = buf_len;
>
> sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 602715fc9a75..0248d6808755 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -65,6 +65,9 @@ virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
> pkt->buf = kmalloc(len, GFP_KERNEL);
> if (!pkt->buf)
> goto out_pkt;
> +
> + pkt->buf_len = len;
> +
> err = memcpy_from_msg(pkt->buf, info->msg, len);
> if (err)
> goto out;
> @@ -86,6 +89,46 @@ virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
> return NULL;
> }
>
> +static struct virtio_vsock_buf *
> +virtio_transport_alloc_buf(struct virtio_vsock_pkt *pkt, bool zero_copy)
> +{
> + struct virtio_vsock_buf *buf;
> +
> + if (pkt->len == 0)
> + return NULL;
> +
> + buf = kzalloc(sizeof(*buf), GFP_KERNEL);
> + if (!buf)
> + return NULL;
> +
> + /* If the buffer in the virtio_vsock_pkt is full, we can move it to
> + * the new virtio_vsock_buf avoiding the copy, because we are sure that
> + * we are not use more memory than that counted by the credit mechanism.
> + */
> + if (zero_copy && pkt->len == pkt->buf_len) {
> + buf->addr = pkt->buf;
> + pkt->buf = NULL;
> + } else {

Is the copy still needed if we're just few bytes less? We meet similar
issue for virito-net, and virtio-net solve this by always copy first
128bytes for big packets.

See receive_big().

Thanks

> + buf->addr = kmalloc(pkt->len, GFP_KERNEL);
> + if (!buf->addr) {
> + kfree(buf);
> + return NULL;
> + }
> +
> + memcpy(buf->addr, pkt->buf, pkt->len);
> + }
> +
> + buf->len = pkt->len;
> +
> + return buf;
> +}
> +
> +static void virtio_transport_free_buf(struct virtio_vsock_buf *buf)
> +{
> + kfree(buf->addr);
> + kfree(buf);
> +}
> +
> /* Packet capture */
> static struct sk_buff *virtio_transport_build_skb(void *opaque)
> {
> @@ -190,17 +233,15 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> return virtio_transport_get_ops()->send_pkt(pkt);
> }
>
> -static void virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> - struct virtio_vsock_pkt *pkt)
> +static void virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, u32 len)
> {
> - vvs->rx_bytes += pkt->len;
> + vvs->rx_bytes += len;
> }
>
> -static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
> - struct virtio_vsock_pkt *pkt)
> +static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs, u32 len)
> {
> - vvs->rx_bytes -= pkt->len;
> - vvs->fwd_cnt += pkt->len;
> + vvs->rx_bytes -= len;
> + vvs->fwd_cnt += len;
> }
>
> void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
> @@ -254,36 +295,36 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> size_t len)
> {
> struct virtio_vsock_sock *vvs = vsk->trans;
> - struct virtio_vsock_pkt *pkt;
> + struct virtio_vsock_buf *buf;
> size_t bytes, total = 0;
> int err = -EFAULT;
>
> spin_lock_bh(&vvs->rx_lock);
> while (total < len && !list_empty(&vvs->rx_queue)) {
> - pkt = list_first_entry(&vvs->rx_queue,
> - struct virtio_vsock_pkt, list);
> + buf = list_first_entry(&vvs->rx_queue,
> + struct virtio_vsock_buf, list);
>
> bytes = len - total;
> - if (bytes > pkt->len - pkt->off)
> - bytes = pkt->len - pkt->off;
> + if (bytes > buf->len - buf->off)
> + bytes = buf->len - buf->off;
>
> /* sk_lock is held by caller so no one else can dequeue.
> * Unlock rx_lock since memcpy_to_msg() may sleep.
> */
> spin_unlock_bh(&vvs->rx_lock);
>
> - err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
> + err = memcpy_to_msg(msg, buf->addr + buf->off, bytes);
> if (err)
> goto out;
>
> spin_lock_bh(&vvs->rx_lock);
>
> total += bytes;
> - pkt->off += bytes;
> - if (pkt->off == pkt->len) {
> - virtio_transport_dec_rx_pkt(vvs, pkt);
> - list_del(&pkt->list);
> - virtio_transport_free_pkt(pkt);
> + buf->off += bytes;
> + if (buf->off == buf->len) {
> + virtio_transport_dec_rx_pkt(vvs, buf->len);
> + list_del(&buf->list);
> + virtio_transport_free_buf(buf);
> }
> }
> spin_unlock_bh(&vvs->rx_lock);
> @@ -841,20 +882,24 @@ virtio_transport_recv_connected(struct sock *sk,
> {
> struct vsock_sock *vsk = vsock_sk(sk);
> struct virtio_vsock_sock *vvs = vsk->trans;
> + struct virtio_vsock_buf *buf;
> int err = 0;
>
> switch (le16_to_cpu(pkt->hdr.op)) {
> case VIRTIO_VSOCK_OP_RW:
> pkt->len = le32_to_cpu(pkt->hdr.len);
> - pkt->off = 0;
> + buf = virtio_transport_alloc_buf(pkt, true);
>
> - spin_lock_bh(&vvs->rx_lock);
> - virtio_transport_inc_rx_pkt(vvs, pkt);
> - list_add_tail(&pkt->list, &vvs->rx_queue);
> - spin_unlock_bh(&vvs->rx_lock);
> + if (buf) {
> + spin_lock_bh(&vvs->rx_lock);
> + virtio_transport_inc_rx_pkt(vvs, pkt->len);
> + list_add_tail(&buf->list, &vvs->rx_queue);
> + spin_unlock_bh(&vvs->rx_lock);
>
> - sk->sk_data_ready(sk);
> - return err;
> + sk->sk_data_ready(sk);
> + }
> +
> + break;
> case VIRTIO_VSOCK_OP_CREDIT_UPDATE:
> sk->sk_write_space(sk);
> break;