[PATCH 2/5] vsock/virtio: Resize receive buffers so that each SKB fits in a page

[Will Deacon <will@kernel.org>]

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@kernel.org>
---
 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)
 #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
 #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
 
-- 
2.50.0.714.g196bf9f422-goog