Re: [PATCH] jffs2 summary allocation

Kyungmin Park
2008-04-05T01:29:27Z

On Sat, Apr 5, 2008 at 10:11 AM, Josh Boyer <jwboyer@gmail.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