linux-kernel - Re: [PATCH] zram: rework reset and destroy path

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Date:	Wed, 4 Feb 2015 09:35:10 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ganesh Mahendran <opensource.ganesh@...il.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
	nefelim4ag@...il.com, eternaleye@...il.com
Subject: Re: [PATCH] zram: rework reset and destroy path

On Wed, Feb 04, 2015 at 09:24:51AM +0900, Sergey Senozhatsky wrote:
> Hello Minchan,
> 
> On (02/04/15 08:42), Minchan Kim wrote:
> > > +	kfree(zram_devices);
> > > +	unregister_blkdev(zram_major, "zram");
> > > +	pr_debug("Destroyed %u device(s)\n", nr);
> > 
> > Create_device just shows the number of created device so I think
> > no worth to emit per-device information in destroy_devices.
> > Let's just emit clean up done like old in zram_exit but
> > use pr_info instead of pr_debug.
> 
> not critical let's keep it as is (it just mirrors the message from init()),
> and I wouldn't say it's totally useless now. we allocate space for devices,
> disk, queue, etc. and we destroy it here.

As I said, it is just minor but at least want to fix pr_debug into
pr_info.

> 
> please see below.
> 
> > Another concern is I'd like to keep per-device interface(e,g.
> > create_device, destroy_device) because there was requirement
> > to add new zram device dynamically. I guess you could remember
> > that. Although I didn't have a enough time to response,
> > Alex finally convinced me so I hope a contributor who have time
> > will do it if he has an interest about that.
> 
> yes, I was going to tell you that perhaps I'll do that. I had several
> discussions on google+ and it seems that people want to see this
> feature. so I was going to ask your opinion.
> 
> the solution I'm thinking about now is to replace zram devices fixed
> size array with a list, protected by mutex or spin lock (doesn't
> matter at this point). this will change destroy_devices() from array
> iteration to destroy each list entry.

Yeb.

> 
> so:
> a)	pr_debug("Destroyed %u device(s)\n", nr)
> it will show the actual number of active devices by that time.
> 
> b) I'll refactor destroy_devices().
> 
> this rework will not make it into the upcoming merge window, so we'll
> have enough time.
> 
> I haven't decided yet, if I wan't to keep released zram devices in the
> list (idle zram devices list, picking up the first available device
> when user requests new zram device) or I will destroy abondoned devices
> and , thus, the list will represent only active devices.

I perfer destroy abandoned devices.

> 
> 
> I tend to select the latter one -- destroy unused zram devices. I don't
> want to give additional sysfs knob to limit the number of idle devices,
> waste memory for idle devices, etc. We already  have a number of quite
> complicated knobs.

True.

-- 
Kind regards,
Minchan Kim
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