Re: [PATCH RFC 4/6] btrfs: Check if the filesystem is has mixed type of devices

[Michał Mirosław]

On Tue, Feb 09, 2021 at 09:30:38PM +0100, Michal Rostecki wrote:
> From: Michal Rostecki <mroste...@suse.com>
> 
> Add the btrfs_check_mixed() function which checks if the filesystem has
> the mixed type of devices (non-rotational and rotational). This
> information is going to be used in roundrobin raid1 read policy.a
[...]
> @@ -669,8 +699,12 @@ static int btrfs_open_one_device(struct btrfs_fs_devices 
> *fs_devices,
>       }
>  
>       q = bdev_get_queue(bdev);
> -     if (!blk_queue_nonrot(q))
> +     rotating = !blk_queue_nonrot(q);
> +     device->rotating = rotating;
> +     if (rotating)
>               fs_devices->rotating = true;
> +     if (!fs_devices->mixed)
> +             fs_devices->mixed = btrfs_check_mixed(fs_devices, rotating);
[...]

Since this is adding to a set, a faster way is:

if (fs_devices->rotating != rotating)
        fs_devices->mixed = true;

The scan might be necessary on device removal, though.

> -     if (!blk_queue_nonrot(q))
> +     rotating = !blk_queue_nonrot(q);
> +     device->rotating = rotating;
> +     if (rotating)
>               fs_devices->rotating = true;
> +     if (!fs_devices->mixed)
> +             fs_devices->mixed = btrfs_check_mixed(fs_devices, rotating);

Duplication. Maybe pull all this into a function?

Best Regards,
Michał Mirosław