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:

quoted

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

quoted

+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