linux-kernel - Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support large-page Nand chip

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Date:	Mon, 05 Dec 2011 08:47:03 +0200
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	shuo.liu@...escale.com
Cc:	dwmw2@...radead.org, Artem.Bityutskiy@...ia.com,
	scottwood@...escale.com, linux-mtd@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, leoli@...escale.com
Subject: Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support
 large-page Nand chip

On Sun, 2011-12-04 at 12:31 +0800, shuo.liu@...escale.com wrote:
> +		/*
> +		 * Freescale FCM controller has a 2K size limitation of buffer
> +		 * RAM, so elbc_fcm_ctrl->buffer have to be used if writesize
> +		 * of chip is greater than 2048.
> +		 * We malloc a large enough buffer (maximum page size is 16K).
> +		 */
> +		elbc_fcm_ctrl->buffer = kmalloc(1024 * 16 + 1024, GFP_KERNEL);
> +		if (!elbc_fcm_ctrl->buffer) {
> +			dev_err(dev, "failed to allocate memory\n");
> +			mutex_unlock(&fsl_elbc_nand_mutex);
> +			ret = -ENOMEM;
> +			goto err;
> +		}

Sorry for returning to this again and agian - I do not have time to dig
suggest you the right solutions on the one hand, you do not provide me a
good answer on the other hand (or I forgot?).

16KiB pages do not even exist I believe. And you kmalloc 33KiB or RAM
although in most cases you need only 5KiB. I think this is wrong - what
is the very strong reason of wasting RAM you have?

Why you cannot allocate exactly the required amount of RAM after
'nand_scan_ident()' finishes and you know the page size?

Artem.

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