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

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Date:	Fri, 4 Apr 2008 19:41:34 -0700
From:	David Brownell <david-b@...bell.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kyungmin Park" <kmpark@...radead.org>,
	"Josh Boyer" <jwboyer@...il.com>, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org,
	"Michael Trimarchi" <trimarchimichael@...oo.it>,
	spi-devel-general@...ts.sourceforge.net, dwmw2@...radead.org,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH] jffs2 summary allocation

On Friday 04 April 2008, Andrew Morton wrote:
> This problem comes up pretty often. 

Which problem -- kmalloc(BIG)?  Or dma(dma-unsafe-mem)?
Or something else?

The specific issue here might best be described as JFFS2
making a bad assumption:  that MTD drivers never use DMA.
The I2C stack does that in some cases (for example, I/O
buffers in i2c_smbus_xfer_emulated are on-stack), but I'd
not call that an especially common assumption.

> Rather than open-coding it yet again 
> it'd be nice to have a little bit of library code which manages an array of
> pages and which has accessors for common operations like
> read/write-u8/u16/u32/u64, memset, memcpy, etc.

If array-of-pages is to be more widely adopted, that'd
make sense.  The MTD framework is a bit odd in that
respect ... it has block devices but doesn't use the
scatterlist primitives.

- Dave
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