Re: [PATCH 05/11] vhost: move vq iovec allocation to dev init time

* Re: [PATCH 05/11] vhost: move vq iovec allocation to dev init time
       [not found] ` <1604528804-2878-6-git-send-email-michael.christie@oracle.com>
@ 2020-11-09  3:41   ` Jason Wang
  0 siblings, 0 replies; 5+ messages in thread
From: Jason Wang @ 2020-11-09  3:41 UTC (permalink / raw)
  To: Mike Christie, martin.petersen, linux-scsi, target-devel, mst,
	pbonzini, stefanha, virtualization

On 2020/11/5 上午6:26, Mike Christie wrote:
> The next patches allow us to create vqs on demand after vhost_dev_init
> and vhost_dev_set_owner have been called. For vhost-scsi we don't
> know the number of vqs we really want until the vring/vq setup
> operations have started up. For other devices we know the number of vqs
> at vhost_dev_init time, so for those devs we init the vq and allocate
> the needed iovecs. For vhost-scsi we will do it later when userspace has
> indicated to us that it's going to use a vq.
>
> Signed-off-by: Mike Christie <michael.christie@oracle.com>
> ---
>   drivers/vhost/vhost.c | 71 +++++++++++++++++++++++++++------------------------
>   1 file changed, 38 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index b35229e..a4a4450 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -383,29 +383,27 @@ static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
>   	vq->heads = NULL;
>   }
>   
> -/* Helper to allocate iovec buffers for all vqs. */
> -static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
> +static int vhost_vq_alloc_iovecs(struct vhost_dev *dev,
> +				 struct vhost_virtqueue *vq)
>   {
> -	struct vhost_virtqueue *vq;
> -	int i;
> +	vq->indirect = kmalloc_array(UIO_MAXIOV, sizeof(*vq->indirect),
> +				     GFP_KERNEL);
> +	if (!vq->indirect)
> +		return -ENOMEM;
> +
> +	if (!dev->iov_limit)
> +		return 0;

This looks like an optimization. Let's try to defer this into another patch.

> +
> +	vq->log = kmalloc_array(dev->iov_limit, sizeof(*vq->log), GFP_KERNEL);
> +	vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads),
> +				  GFP_KERNEL);
> +	if (!vq->log || !vq->heads)
> +		goto err_nomem;
>   
> -	for (i = 0; i < dev->nvqs; ++i) {
> -		vq = dev->vqs[i];
> -		vq->indirect = kmalloc_array(UIO_MAXIOV,
> -					     sizeof(*vq->indirect),
> -					     GFP_KERNEL);
> -		vq->log = kmalloc_array(dev->iov_limit, sizeof(*vq->log),
> -					GFP_KERNEL);
> -		vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads),
> -					  GFP_KERNEL);
> -		if (!vq->indirect || !vq->log || !vq->heads)
> -			goto err_nomem;
> -	}
>   	return 0;
>   
>   err_nomem:
> -	for (; i >= 0; --i)
> -		vhost_vq_free_iovecs(dev->vqs[i]);
> +	vhost_vq_free_iovecs(vq);
>   	return -ENOMEM;
>   }
>   
> @@ -458,6 +456,21 @@ static size_t vhost_get_desc_size(struct vhost_virtqueue *vq,
>   	return sizeof(*vq->desc) * num;
>   }
>   
> +static int vhost_vq_init(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> +{
> +	vq->log = NULL;
> +	vq->indirect = NULL;
> +	vq->heads = NULL;
> +	vq->dev = dev;
> +	mutex_init(&vq->mutex);
> +	vhost_vq_reset(dev, vq);
> +
> +	if (vq->handle_kick)
> +		vhost_poll_init(&vq->poll, vq->handle_kick, EPOLLIN, dev);
> +
> +	return vhost_vq_alloc_iovecs(dev, vq);
> +}

If it's possible, I would do a patch to introduce vhost_vq_init() and 
then add vhost_vq_alloc_iovecs() on top.

Thanks

> +
>   int vhost_dev_init(struct vhost_dev *dev,
>   		   struct vhost_virtqueue **vqs, int nvqs,
>   		   int iov_limit, int weight, int byte_weight,
> @@ -465,7 +478,6 @@ int vhost_dev_init(struct vhost_dev *dev,
>   		   int (*msg_handler)(struct vhost_dev *dev,
>   				      struct vhost_iotlb_msg *msg))
>   {
> -	struct vhost_virtqueue *vq;
>   	int i;
>   
>   	dev->vqs = vqs;
> @@ -489,19 +501,16 @@ int vhost_dev_init(struct vhost_dev *dev,
>   
>   
>   	for (i = 0; i < dev->nvqs; ++i) {
> -		vq = dev->vqs[i];
> -		vq->log = NULL;
> -		vq->indirect = NULL;
> -		vq->heads = NULL;
> -		vq->dev = dev;
> -		mutex_init(&vq->mutex);
> -		vhost_vq_reset(dev, vq);
> -		if (vq->handle_kick)
> -			vhost_poll_init(&vq->poll, vq->handle_kick,
> -					EPOLLIN, dev);
> +		if (vhost_vq_init(dev, dev->vqs[i]))
> +			goto err_vq_init;
>   	}
>   
>   	return 0;
> +
> +err_vq_init:
> +	for (--i; i >= 0; --i)
> +		vhost_vq_free_iovecs(dev->vqs[i]);
> +	return -ENOMEM;
>   }
>   EXPORT_SYMBOL_GPL(vhost_dev_init);
>   
> @@ -606,10 +615,6 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>   			goto err_cgroup;
>   	}
>   
> -	err = vhost_dev_alloc_iovecs(dev);
> -	if (err)
> -		goto err_cgroup;
> -
>   	return 0;
>   err_cgroup:
>   	if (dev->worker) {

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