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 --- include/linux/virtio_vsock.h | 1 - net/vmw_vsock/virtio_transport.c | 7 ++++++- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h index eb6980aa19fd..1b5731186095 100644 --- a/include/linux/virtio_vsock.h +++ b/include/linux/virtio_vsock.h @@ -109,7 +109,6 @@ 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_MAX_BUF_SIZE 0xFFFFFFFFUL #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE (1024 * 64) diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c index 488e6ddc6ffa..3daba06ed499 100644 --- a/net/vmw_vsock/virtio_transport.c +++ b/net/vmw_vsock/virtio_transport.c @@ -307,7 +307,12 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk) static void virtio_vsock_rx_fill(struct virtio_vsock *vsock) { - int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM; + /* Dimension the SKB so that the entire thing fits exactly into + * a single page. This avoids wasting memory due to alloc_skb() + * rounding up to the next page order and also means that we + * don't leave higher-order pages sitting around in the RX queue. + */ + int total_len = SKB_WITH_OVERHEAD(PAGE_SIZE); struct scatterlist pkt, *p; struct virtqueue *vq; struct sk_buff *skb; -- 2.50.0.727.gbf7dc18ff4-goog