linux-kernel - Re: [PATCH 02/10] Remove need for explicit device initialization

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Date:	Tue, 10 Aug 2010 09:08:44 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Pekka Enberg <penberg@...helsinki.fi>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Linux Driver Project <devel@...uxdriverproject.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/10] Remove need for explicit device initialization

On 08/10/2010 12:06 AM, Pekka Enberg wrote:
> On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@...are.org> wrote:
>> Currently, the user has to explicitly write a positive value to
>> initstate sysfs node before the device can be used. This event
>> triggers allocation of per-device metadata like memory pool,
>> table array and so on.
>>
>> We do not pre-initialize all zram devices since the 'table' array,
>> mapping disk blocks to compressed chunks, takes considerable amount
>> of memory (8 bytes per page). So, pre-initializing all devices will
>> be quite wasteful if only few or none of the devices are actually
>> used.
>>
>> This explicit device initialization from user is an odd requirement and
>> can be easily avoided. We now initialize the device when first write is
>> done to the device.
>>
>> Signed-off-by: Nitin Gupta <ngupta@...are.org>
> 
> AFAICT, most hardware block device drivers do things like this in the
> probe function. Why can't we do that for zram as well and drop the
> ->init_done and ->init_lock parts?
> 

I think probe is only for PCI devices? Maybe should hook into open function
in struct block_device_operations. That way, we can also drop init_done and
init_lock parts.

Thanks,
Nitin
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