On Fri, Jun 27, 2025 at 12:41:48PM +0200, Stefano Garzarella wrote: > On Wed, Jun 25, 2025 at 02:15:40PM +0100, Will Deacon wrote: > > When allocating receive buffers for the vsock virtio RX virtqueue, an > > SKB is allocated with a 4140 data payload (the 44-byte packet header + > > VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE). Even when factoring in the SKB > > overhead, the resulting 8KiB allocation thanks to the rounding in > > kmalloc_reserve() is wasteful (~3700 unusable bytes) and results in a > > higher-order page allocation for the sake of a few hundred bytes of > > packet data. > > > > Limit the vsock virtio RX buffers to a page per SKB, resulting in much > > better memory utilisation and removing the need to allocate higher-order > > pages entirely. > > > > Signed-off-by: Will Deacon <[email protected]> > > --- > > include/linux/virtio_vsock.h | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h > > index 36fb3edfa403..67ffb64325ef 100644 > > --- a/include/linux/virtio_vsock.h > > +++ b/include/linux/virtio_vsock.h > > @@ -111,7 +111,8 @@ static inline size_t virtio_vsock_skb_len(struct > > sk_buff *skb) > > return (size_t)(skb_end_pointer(skb) - skb->head); > > } > > > > -#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE (1024 * 4) > > +#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE (SKB_WITH_OVERHEAD(PAGE_SIZE) \ > > + - VIRTIO_VSOCK_SKB_HEADROOM) > > This is only used in net/vmw_vsock/virtio_transport.c : > > static void virtio_vsock_rx_fill(struct virtio_vsock *vsock) > { > int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE + > VIRTIO_VSOCK_SKB_HEADROOM; > > > What about just remove VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE and use > `SKB_WITH_OVERHEAD(PAGE_SIZE)` there? (maybe with a comment summarizing > the issue we found).
Sure, works for me. That gets rid of the funny +- VIRTIO_VSOCK_SKB_HEADROOM too. Will
