linux-kernel - Re: [PATCH v3 15/15] vsock/virtio: reorder fields to reduce padding

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Message-ID: <aXsclvInQFIuFe5i@sgarzare-redhat>
Date: Thu, 29 Jan 2026 09:42:06 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>, 
	Jonathan Corbet <corbet@....net>, Olivia Mackall <olivia@...enic.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Jason Wang <jasowang@...hat.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
	Eugenio Pérez <eperezma@...hat.com>, "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Gerd Hoffmann <kraxel@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Robin Murphy <robin.murphy@....com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Petr Tesarik <ptesarik@...e.com>, Leon Romanovsky <leon@...nel.org>, 
	Jason Gunthorpe <jgg@...pe.ca>, Bartosz Golaszewski <brgl@...nel.org>, linux-doc@...r.kernel.org, 
	linux-crypto@...r.kernel.org, virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org, 
	iommu@...ts.linux.dev, kvm@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v3 15/15] vsock/virtio: reorder fields to reduce padding

On Wed, Jan 28, 2026 at 03:31:21PM -0500, Michael S. Tsirkin wrote:
>Reorder struct virtio_vsock fields to place the DMA buffer (event_list)
>last. This eliminates the padding from aligning the struct size on
>ARCH_DMA_MINALIGN.
>
>Suggested-by: Stefano Garzarella <sgarzare@...hat.com>
>Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>---
>
>changes from v2:
>	move event_lock and event_run too, to keep
>	event things logically together, as suggested by
>	Stefano Garzarella.

Thanks for that!

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

>
>Note: this is the only change in v3 and it's cosmetic, so I am
>not reposting the whole patchset.
>
>
> net/vmw_vsock/virtio_transport.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index 999a0839726a..b333a7591b26 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -55,15 +55,6 @@ struct virtio_vsock {
> 	int rx_buf_nr;
> 	int rx_buf_max_nr;
>
>-	/* The following fields are protected by event_lock.
>-	 * vqs[VSOCK_VQ_EVENT] must be accessed with event_lock held.
>-	 */
>-	struct mutex event_lock;
>-	bool event_run;
>-	__dma_from_device_group_begin();
>-	struct virtio_vsock_event event_list[8];
>-	__dma_from_device_group_end();
>-
> 	u32 guest_cid;
> 	bool seqpacket_allow;
>
>@@ -77,6 +68,15 @@ struct virtio_vsock {
> 	 */
> 	struct scatterlist *out_sgs[MAX_SKB_FRAGS + 1];
> 	struct scatterlist out_bufs[MAX_SKB_FRAGS + 1];
>+
>+	/* The following fields are protected by event_lock.
>+	 * vqs[VSOCK_VQ_EVENT] must be accessed with event_lock held.
>+	 */
>+	struct mutex event_lock;
>+	bool event_run;
>+	__dma_from_device_group_begin();
>+	struct virtio_vsock_event event_list[8];
>+	__dma_from_device_group_end();
> };
>
> static u32 virtio_transport_get_local_cid(void)
>-- 
>MST
>