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

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Message-Id: <20250625131543.5155-3-will@kernel.org>
Date: Wed, 25 Jun 2025 14:15:40 +0100
From: Will Deacon <will@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Will Deacon <will@...nel.org>,
	Keir Fraser <keirf@...gle.com>,
	Steven Moreland <smoreland@...gle.com>,
	Frederick Mayle <fmayle@...gle.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	netdev@...r.kernel.org,
	virtualization@...ts.linux.dev
Subject: [PATCH 2/5] vsock/virtio: Resize receive buffers so that each SKB fits in a 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 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@...nel.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