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

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Message-ID: <AANLkTinsoHUb307N+v6pGfRraHK-epBU70fD0FxPCNup@mail.gmail.com>
Date:	Mon, 9 Aug 2010 21:36:53 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Nitin Gupta <ngupta@...are.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 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?
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