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

Stefano Garzarella
2019-05-17T08:25:16Z

On Thu, May 16, 2019 at 04:25:33PM +0100, Stefan Hajnoczi wrote:
> 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.
>

Sure, I'll fix it.

> > +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.
>

IIUC, in the case of zero-copy I should allocate only the buf,
otherwise I should allocate both buf and buf->addr in a single call
when I'm doing a full-copy.

Is it correct?

> > @@ -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.

I'll return -ENOMEM when the allocation fails.

Thanks,
Stefano