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

Stefan Hajnoczi
2019-05-16T15:25:42Z

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On Fri, May 10, 2019 at 02:58:36PM +0200, Stefano Garzarella wrote:
> +struct virtio_vsock_buf {

Please add a comment describing the purpose of this struct and to
differentiate its use from struct virtio_vsock_pkt.

> +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 {
> + buf->addr = kmalloc(pkt->len, GFP_KERNEL);

buf and buf->addr could be allocated in a single call, though I'm not
sure how big an optimization this is.

> @@ -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);
> + }

The return value of this function isn't used but the code still makes an
effort to return errors. Please return -ENOMEM when buf == NULL.

If you'd like to remove the return value that's fine too, but please do
it for the whole function to be consistent.

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