linux-kernel - Re: zram: device management utility needed

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Message-ID: <20140805081238.GA3700@gmail.com>
Date:	Tue, 5 Aug 2014 08:12:47 +0000
From:	Minchan Kim <minchan@...nel.org>
To:	Karel Zak <kzak@...hat.com>
Cc:	Sami Kerola <kerolasa@....fi>, util-linux@...r.kernel.org,
	Timofey Titovets <nefelim4ag@...il.com>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: zram: device management utility needed

On Tue, Aug 05, 2014 at 09:07:16AM +0200, Karel Zak wrote:
> On Tue, Aug 05, 2014 at 11:00:24AM +0900, Minchan Kim wrote:
> > On Wed, Jul 30, 2014 at 12:14:42AM +0100, Sami Kerola wrote:
> > > The zram devices are not created by any sort of equipment appearing in a
> > > bus so an method of creating new or removing existing devices will be
> > > needed.  When the zram module is loaded it should create
> > > /dev/zram-control device, that responds to ioctl() calls[4].  The calls
> > > could be similar with /dev/loop-control[5], that allow adding or removing
> > > specified device, and discover adding a free device.
> > 
> > Normally, dynamic management is good to have, I think but I didn't hear
> > strong requirement for that until now.
> 
> I guess that number of zram devices will be always relatively small
> compare to /dev/loopN devices. It is not unusual that people use
> systems with more than 256 loop devs, so /dev/loop-control makes a lot
> of sense to keep the device management effective and simple.
> 
> > Why don't you change num_device param at module loading time?
> 
> If you have really many loopN devices than create all the nodes at
> boot time means extra overhead (allocate nodes in kernel, events to
> udev, create /dev files etc.).  The ioctl LOOP_CTL_* API also provides
> LOOP_CTL_GET_FREE that returns unused device, so you don't have to
> scan all the /dev/loopN devices to detect a free device.

Thanks for the info!

> 
> > I'd like to hear real scenario from whom are about to using that faeture
> > right now and what's the problem with num_device param.
> 
> Again, I don't think it's so important for zram as for loop devices.
> All depends how people will use zram devices. We will see...

Yeb and we can do it when we see.

> 
>     Karel
> 
> -- 
>  Karel Zak  <kzak@...hat.com>
>  http://karelzak.blogspot.com
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