linux-kernel - Re: [PATCH] jffs2 summary allocation

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Date:	Sat, 5 Apr 2008 10:29:25 +0900
From:	"Kyungmin Park" <kmpark@...radead.org>
To:	"Josh Boyer" <jwboyer@...il.com>
Cc:	"David Brownell" <david-b@...bell.net>,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	"Michael Trimarchi" <trimarchimichael@...oo.it>,
	spi-devel-general@...ts.sourceforge.net,
	"Andrew Morton" <akpm@...ux-foundation.org>, dwmw2@...radead.org,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH] jffs2 summary allocation

On Sat, Apr 5, 2008 at 10:11 AM, Josh Boyer <jwboyer@...il.com> wrote:
> On Fri, 2008-04-04 at 16:58 -0700, David Brownell wrote:
>  > On Friday 04 April 2008, Josh Boyer wrote:
>  > >
>  > > >   ... This means specifically that you may _not_ use the
>  > > >   memory/addresses returned from vmalloc() for DMA.  ...
>  > > >
>  > > > So I'm rather surprised to see *ANY* kernel code trying to do
>  > > > that.  That rule has been in effect for many, many years now.
>  > >
>  > > I don't think it was intentional.  You're going through several layers
>  > > here:
>  > >
>  > > JFFS2 -> mtd parts -> mtd dataflash -> atmel_spi.
>  > >
>  > > Typically MTD drivers aren't doing DMAs to flash and JFFS2 has no idea
>  > > which particular chip driver is being used because it's abstracted by
>  > > MTD.
>  >
>  > That's true ... although I can imagine using DMA to
>  > avoid dcache trashing if its setup cost is low enough,
>  > with either NAND or NOR chips.
>  >
>  > Still:  in this context vmalloc() is wrong.
>
>  Agreed.  One issue is that the summary code allocates a buffer that
>  equals the eraseblock size of the underlying MTD device.  For larger
>  NAND chips, that may be up to 256KiB.  I believe this is within the
>  allowable kmalloc size for most architectures these days, but the
>  summary code is 3 years old and was likely expecting a smaller limit.
>  And there is always the question on whether finding that much contiguous
>  memory will be an issue.

In MLC chips it goes up to 512KiB. It means it can't allocate the
eraseblock size memory with kmalloc().
In ARM environment I can't see the 256KiB or more memory allocation
with kmalloc().
So I now changed the kmalloc eraseblock to vmalloc at both jffs2 and mtd-utils.

Thank you,
Kyungmin Park
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