Linux Virtualization - May 2019 - [PATCH v2 1/8] vsock/virtio: limit the memory used per-socket

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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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

On Fri, May 17, 2019 at 10:25:05AM +0200, Stefano Garzarella
wrote:
> 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:
> > > +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?
Yes, but it's your choice whether optimization is worthwhile.  If it
increases the complexity of the code and doesn't result in a measurable
improvement, then it's not worth it.

Stefan
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