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

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Message-ID: <20210210125014.GC23499@wotan.suse.de>
Date:   Wed, 10 Feb 2021 12:50:14 +0000
From:   Michal Rostecki <mrostecki@...e.de>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        "open list:BTRFS FILE SYSTEM" <linux-btrfs@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Michal Rostecki <mrostecki@...e.com>
Subject: Re: [PATCH RFC 4/6] btrfs: Check if the filesystem is has mixed type
 of devices

On Wed, Feb 10, 2021 at 05:08:05AM +0100, Michał Mirosław wrote:
> On Tue, Feb 09, 2021 at 09:30:38PM +0100, Michal Rostecki wrote:
> > From: Michal Rostecki <mrostecki@...e.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;
> 

Good idea.

> The scan might be necessary on device removal, though.
> 

And good point. I didn't address the case of device removal at all.

> > -	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?
> 

Will do that as well.

> Best Regards,
> Michał Mirosław

Regards,
Michal