netdev - Re: [PATCH v9 07/32] virtio_ring: split: extract the logic of alloc state and extra

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Date:   Wed, 13 Apr 2022 14:48:06 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, netdev@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v9 07/32] virtio_ring: split: extract the logic of alloc state and extra

On Tue, 12 Apr 2022 11:26:49 +0800, Jason Wang <jasowang@...hat.com> wrote:
>
> 在 2022/4/6 上午11:43, Xuan Zhuo 写道:
> > Separate the logic of creating desc_state, desc_extra, and subsequent
> > patches will call it independently.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >   drivers/virtio/virtio_ring.c | 53 ++++++++++++++++++++++++++----------
> >   1 file changed, 38 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 72d5ae063fa0..6de67439cb57 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -198,6 +198,7 @@ struct vring_virtqueue {
> >   #endif
> >   };
> >
> > +static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
> >
> >   /*
> >    * Helpers.
> > @@ -915,6 +916,33 @@ static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> >   	return NULL;
> >   }
> >
> > +static int vring_alloc_state_extra_split(u32 num,
> > +					 struct vring_desc_state_split **desc_state,
> > +					 struct vring_desc_extra **desc_extra)
> > +{
> > +	struct vring_desc_state_split *state;
> > +	struct vring_desc_extra *extra;
> > +
> > +	state = kmalloc_array(num, sizeof(struct vring_desc_state_split), GFP_KERNEL);
> > +	if (!state)
> > +		goto err_state;
> > +
> > +	extra = vring_alloc_desc_extra(num);
> > +	if (!extra)
> > +		goto err_extra;
> > +
> > +	memset(state, 0, num * sizeof(struct vring_desc_state_split));
> > +
> > +	*desc_state = state;
> > +	*desc_extra = extra;
> > +	return 0;
> > +
> > +err_extra:
> > +	kfree(state);
> > +err_state:
> > +	return -ENOMEM;
> > +}
> > +
> >   static void *vring_alloc_queue_split(struct virtio_device *vdev,
> >   				     dma_addr_t *dma_addr,
> >   				     u32 *n,
> > @@ -2196,7 +2224,10 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   					void (*callback)(struct virtqueue *),
> >   					const char *name)
> >   {
> > +	struct vring_desc_state_split *state;
> > +	struct vring_desc_extra *extra;
> >   	struct vring_virtqueue *vq;
> > +	int err;
> >
> >   	if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
> >   		return NULL;
> > @@ -2246,30 +2277,22 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   					vq->split.avail_flags_shadow);
> >   	}
> >
> > -	vq->split.desc_state = kmalloc_array(vring.num,
> > -			sizeof(struct vring_desc_state_split), GFP_KERNEL);
> > -	if (!vq->split.desc_state)
> > -		goto err_state;
> > +	err = vring_alloc_state_extra_split(vring.num, &state, &extra);
>
>
> Nit: we can pass e.g &vq->split.desc_state here to avoid extra temp
> variable and assignment.

The reason for not doing this is that when we implement resize later, when we
call vring_alloc_state_extra_split(), we want to keep the old desc_state, and
desc_extra because we want to release them.

As discussed in patch 11, 12, struct vring_virtqueue_split will optimize this
logic.

Thanks.

>
> Other looks good.
>
> Thanks
>
>
> > +	if (err) {
> > +		kfree(vq);
> > +		return NULL;
> > +	}
> >
> > -	vq->split.desc_extra = vring_alloc_desc_extra(vring.num);
> > -	if (!vq->split.desc_extra)
> > -		goto err_extra;
> > +	vq->split.desc_state = state;
> > +	vq->split.desc_extra = extra;
> >
> >   	/* Put everything in free lists. */
> >   	vq->free_head = 0;
> > -	memset(vq->split.desc_state, 0, vring.num *
> > -			sizeof(struct vring_desc_state_split));
> >
> >   	spin_lock(&vdev->vqs_list_lock);
> >   	list_add_tail(&vq->vq.list, &vdev->vqs);
> >   	spin_unlock(&vdev->vqs_list_lock);
> >   	return &vq->vq;
> > -
> > -err_extra:
> > -	kfree(vq->split.desc_state);
> > -err_state:
> > -	kfree(vq);
> > -	return NULL;
> >   }
> >   EXPORT_SYMBOL_GPL(__vring_new_virtqueue);
> >
>