since when does ARM map the kernel memory in sections?

[Arnd Bergmann]

On Wednesday 27 April 2011, Jamie Lokier wrote:
> Imho, only if there's a use for it.  If this is about whole partitions
> picking up random data corruption, versus not doing so, then I suggest
> the choice of "Reliable Write" vs. "Unreliable Write" be a mount
> option or hdparm-style block device option.
> 
> If there are tighter guarantees, such as "Unreliable Write" corruption
> being limited to the written naturally aligned 1MB blocks (say), and
> it was genuinely faster, that would be really valuable information to
> pass up to filesystems - and to userspace - as you can structure
> reliability around that in lots of ways.

In all the SDHC cards that I have seen, the corruption should be local to
an erase block of the size that is supposedly found in
/sys/block/mmcblk*/device/preferred_erase_size, which is typically 4 MB.

However, I don't think that the standard actually guarantees this and,
worse, some cards that I have seen actually lie about the erase block
size and claim that it is 4 MB when it is actually 1.5, 2, 3 or 8 MB.

For eMMC devices, I don't think we can read the erase block size.

	Arnd