diff options
| author | Will Deacon <will@kernel.org> | 2025-07-17 10:01:11 +0100 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2025-08-01 09:11:09 -0400 |
| commit | 03a92f036a04fed2b00d69f5f46f1a486e70dc5c (patch) | |
| tree | 8e9c259031e3ed99f41fb1a4286f10f5a3afdcd8 | |
| parent | 87dbae5e36613a6020f3d64a2eaeac0a1e0e6dc6 (diff) | |
vsock/virtio: Resize receive buffers so that each SKB fits in a 4K page
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 on systems with 4KiB pages just for the
sake of a few hundred bytes of packet data.
Limit the vsock virtio RX buffers to 4KiB per SKB, resulting in much
better memory utilisation and removing the need to allocate higher-order
pages entirely.
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
Message-Id: <20250717090116.11987-5-will@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
| -rw-r--r-- | include/linux/virtio_vsock.h | 7 | ||||
| -rw-r--r-- | net/vmw_vsock/virtio_transport.c | 2 |
2 files changed, 7 insertions, 2 deletions
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h index 97465f378ade..879f1dfa7d3a 100644 --- a/include/linux/virtio_vsock.h +++ b/include/linux/virtio_vsock.h @@ -106,7 +106,12 @@ 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) +/* Dimension the RX SKB so that the entire thing fits exactly into + * a single 4KiB 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. + */ +#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE SKB_WITH_OVERHEAD(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 0166919f8705..39f346890f7f 100644 --- a/net/vmw_vsock/virtio_transport.c +++ b/net/vmw_vsock/virtio_transport.c @@ -307,7 +307,7 @@ out_rcu: static void virtio_vsock_rx_fill(struct virtio_vsock *vsock) { - int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM; + int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE; struct scatterlist pkt, *p; struct virtqueue *vq; struct sk_buff *skb; |