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 <will@xxxxxxxxxx>
---
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).
Thanks,
Stefano
#define VIRTIO_VSOCK_MAX_BUF_SIZE 0xFFFFFFFFUL
#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE (1024 * 64)
--
2.50.0.714.g196bf9f422-goog
