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

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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@xxxxxxxxxx>
---
  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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