linux-kernel - Re: [PATCH] Fix Oops with Atmel SPI

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Date:	Thu, 15 Apr 2010 17:32:14 +1000
From:	Iwo Mergler <iwo@...l-direct.com.au>
To:	Anders Larsen <al@...rsen.net>
CC:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	Ian McDonnell <ian@...ghtstareng.com>,
	Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org,
	Matthias Kaehlcke <matthias@...hlcke.net>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] Fix Oops with Atmel SPI

Hi Anders,

Anders Larsen wrote:
> Hi Iwo,
> 
> On 2010-04-14 09:30:41, Iwo Mergler wrote:
>> I wouldn't recommend that. MTD erase blocks are 64K or more. In a typical
>> embedded system you will not be able to kmalloc that much memory after
>> a few day's of operation - the page pool gets fragmented.
> 
> the original problem occurs with SPI flashes, which typically have a much
> smaller erase block size (and it only occurs when they are driven by an Atmel
> SoC SPI controller, hence the #ifdefs)
> 
>> A possibly better approach is to arrange for that memory to get allocated
>> at driver start time.
> 
> The buffer in question is indeed allocated _once_ (at the first write
> operation to the device) and only deallocated when the device is unmounted,
> so allocating it at driver load time wouldn't make much difference IMHO.
> 

I'm sorry, I thought you were somewhere else in the MTD source.
The bad block handling code for NAND also has a full erase block
allocation, which happens during runtime. 

You are correct in that the mount time allocation should be
safe, for most systems.

Best regards,

Iwo

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