6.15-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will@kernel.org
[ Upstream commit 03a92f036a04fed2b00d69f5f46f1a486e70dc5c ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/virtio_vsock.h | 7 ++++++- 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 36fb3edfa403..6c00687539cf 100644 --- a/include/linux/virtio_vsock.h +++ b/include/linux/virtio_vsock.h @@ -111,7 +111,12 @@ 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 f0e48e6911fc..f01f9e878106 100644 --- a/net/vmw_vsock/virtio_transport.c +++ b/net/vmw_vsock/virtio_transport.c @@ -307,7 +307,7 @@ 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; + int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE; struct scatterlist pkt, *p; struct virtqueue *vq; struct sk_buff *skb;