Re: [PATCH 1/1] virtio/vsock: Make vsock virtio packet buff size configurable

[Stefano Garzarella]

On Wed, Jul 21, 2021 at 03:30:00PM +0100, Lee Jones wrote:
> From: Ram Muthiah <rammuthiah@xxxxxxxxxx>
>
> After a virtual device has been running for some time, the SLAB
> sustains ever increasing fragmentation. Contributing to this
> fragmentation are the virtio packet buffer allocations which
> are a drain on 64Kb compound pages. Eventually these can't be
> allocated due to fragmentation.
>
> To enable successful allocations for this packet buffer, the
> packet buffer's size needs to be reduced.
>
> In order to enable a reduction without impacting current users,
> this variable is being exposed as a command line parameter.
>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Cc: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Ram Muthiah <rammuthiah@xxxxxxxxxx>
> Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
> include/linux/virtio_vsock.h            | 4 +++-
> net/vmw_vsock/virtio_transport_common.c | 4 ++++
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 35d7eedb5e8e4..8c77d60a74d34 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -7,9 +7,11 @@
> #include <net/sock.h>
> #include <net/af_vsock.h>
>
> +extern uint virtio_transport_max_vsock_pkt_buf_size;
> +
> #define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
> #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
> -#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
> +#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		virtio_transport_max_vsock_pkt_buf_size
>
> enum {
> 	VSOCK_VQ_RX     = 0, /* for host to guest data */
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 169ba8b72a630..d0d913afec8b6 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -26,6 +26,10 @@
> /* Threshold for detecting small packets to copy */
> #define GOOD_COPY_LEN  128
>
> +uint virtio_transport_max_vsock_pkt_buf_size = 1024 * 64;
> +module_param(virtio_transport_max_vsock_pkt_buf_size, uint, 0444);
> +EXPORT_SYMBOL_GPL(virtio_transport_max_vsock_pkt_buf_size);
> +

Maybe better to add an entry under sysfs similar to what Jiang proposed 
here:
https://lists.linuxfoundation.org/pipermail/virtualization/2021-June/054769.html

Thanks,
Stefano