Re: [PATCH v3 1/1] virtio-blk: add num_request_queues module parameter

[Leon Romanovsky <leon@kernel.org>]

On Thu, Sep 02, 2021 at 11:46:22PM +0300, Max Gurtovoy wrote:
> Sometimes a user would like to control the amount of request queues to
> be created for a block device. For example, for limiting the memory
> footprint of virtio-blk devices.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
> 
> changes from v2:
>  - renamed num_io_queues to num_request_queues (from Stefan)
>  - added Reviewed-by signatures (from Stefan and Christoph)
> 
> changes from v1:
>  - use param_set_uint_minmax (from Christoph)
>  - added "Should > 0" to module description
> 
> Note: This commit apply on top of Jens's branch for-5.15/drivers
> 
> ---
>  drivers/block/virtio_blk.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 4b49df2dfd23..aaa2833a4734 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -24,6 +24,23 @@
>  /* The maximum number of sg elements that fit into a virtqueue */
>  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>  
> +static int virtblk_queue_count_set(const char *val,
> +		const struct kernel_param *kp)
> +{
> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> +}
> +
> +static const struct kernel_param_ops queue_count_ops = {
> +	.set = virtblk_queue_count_set,
> +	.get = param_get_uint,
> +};
> +
> +static unsigned int num_request_queues;
> +module_param_cb(num_request_queues, &queue_count_ops, &num_request_queues,
> +		0644);
> +MODULE_PARM_DESC(num_request_queues,
> +		 "Number of request queues to use for blk device. Should > 0");
> +

Won't it limit all virtio block devices to the same limit?

It is very common to see multiple virtio-blk devices on the same system
and they probably need different limits.

Thanks
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