since when does ARM map the kernel memory in sections?

[Peter Wächtler]

Am Mittwoch, 13. April 2011, 17:44:09 schrieb Nicolas Pitre:
> On Wed, 13 Apr 2011, Peter Wächtler wrote:
> > Am Dienstag, 12. April 2011, 21:20:14 schrieb Andrei Warkentin:
> > > How are you mounting your rootfs and what file system are you using?
> > > What sort of corruptions to the super block are you seeing?
> > 
> > It's using ext4 with metadata journalling in ordered mode.
> > I had to check "if it's the FS" - the test programs create lots of
> > directories and files while a timer is armed to issue a soft reset.
> > The partitions where the "stress tests" run on - survive it happily -
> > just the rootfs where almost nothing gets written is severly damaged so
> > that fsck.ext4 will not repair it automatically.
> 
> SD cards are doing their own wear leveling internally and you have no
> control over it.  Some blocks of data may be moved around, affecting a
> separate logical partition, even if you are not actively writing to that
> partition.  Now if you cut power or reset the card while this is
> happening you'll certainly end up with data loss.  Those SD cards are
> made to be both cheap and fast, meaning they're certainly not reliable
> with regards to unexpected interruptions.
> 
> Furthermore, you should have a look at this article and referenced
> material: http://lwn.net/Articles/428584/.
> 
> 

Yes, I know this article - and I know about wear levelling etc.

Data loss is not the biggest problem. The capacity is huge (>>4GB) - therefore 
I wouldn't want to miss journalling - but I was not involved on the decision. 
Ten years ago I carefully ordered the fsync, rename on ext2 on a 64MiB 
CompactFlash - worked well enough.

The vendor knows about the requirements - perhaps learned it with another 
customer ;)

I tried to "smash" the FS without success in the past - but the rootfs was 
mounted via NFS ;) And the partitions that get tortured stay intact - of 
course you can say that the wear levelling switches some blocks - but I don't 
buy it.

Thanks for all the nice work on Linux - Russell included ;)

  Peter