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

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");
+
 static int major;
 static DEFINE_IDA(vd_index_ida);

@@ -501,7 +518,9 @@ static int init_vq(struct virtio_blk *vblk)
        if (err)
                num_vqs = 1;

-       num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
+       num_vqs = min_t(unsigned int,
+                       min_not_zero(num_request_queues, nr_cpu_ids),
+                       num_vqs);

        vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
        if (!vblk->vqs)
--