virtio-fs: limit number of request queues

Virtio-fs devices might allocate significant resources to virtio queues
such as CPU cores that busy poll on the queue. The device indicates how
many request queues it can support and the driver should initialize the
number of queues that they want to utilize.

In this patch we limit the number of initialized request queues to the
number of CPUs, to limit the resource consumption on the device-side
and to prepare for the upcoming multi-queue patch.

Signed-off-by: Peter-Jan Gootzen <pgootzen@nvidia.com>
Signed-off-by: Yoray Zack <yorayz@nvidia.com>
Suggested-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index bb3e941b95031ac199532e6f2057f3df77c2939d..fa4c16abfe101a5f8e7258bce7c3ac1be1a60e0b 100644 (file)
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -751,6 +751,9 @@ static int virtio_fs_setup_vqs(struct virtio_device *vdev,
        if (fs->num_request_queues == 0)
                return -EINVAL;
 
+       /* Truncate nr of request queues to nr_cpu_id */
+       fs->num_request_queues = min_t(unsigned int, fs->num_request_queues,
+                                       nr_cpu_ids);
        fs->nvqs = VQ_REQUEST + fs->num_request_queues;
        fs->vqs = kcalloc(fs->nvqs, sizeof(fs->vqs[VQ_HIPRIO]), GFP_KERNEL);
        if (!fs->vqs)