vhost scsi: alloc vhost_scsi with kvzalloc() to avoid delay

The size of 'struct vhost_scsi' is order-10 (~2.3MB). It may take long time
delay by kzalloc() to compact memory pages by retrying multiple times when
there is a lack of high-order pages. As a result, there is latency to
create a VM (with vhost-scsi) or to hotadd vhost-scsi-based storage.

The prior commit 595cb754 ("vhost/scsi: use vmalloc for order-10
allocation") prefers to fallback only when really needed, while this patch
allocates with kvzalloc() with __GFP_NORETRY implicitly set to avoid
retrying memory pages compact for multiple times.

The __GFP_NORETRY is implicitly set if the size to allocate is more than
PAGE_SZIE and when __GFP_RETRY_MAYFAIL is not explicitly set.

Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Link: https://lore.kernel.org/r/20210123080853.4214-1-dongli.zhang@oracle.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vhost/scsi.c

@@ -1814,12 +1814,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
 	struct vhost_virtqueue **vqs;
 	int r = -ENOMEM, i;
 
-	vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN | __GFP_RETRY_MAYFAIL);
-	if (!vs) {
-		vs = vzalloc(sizeof(*vs));
-		if (!vs)
-			goto err_vs;
-	}
+	vs = kvzalloc(sizeof(*vs), GFP_KERNEL);
+	if (!vs)
+		goto err_vs;
 
 	vqs = kmalloc_array(VHOST_SCSI_MAX_VQ, sizeof(*vqs), GFP_KERNEL);
 	if (!vqs)