Re: [RFC PATCH 2/3] support for broken memory modules (BadRAM)

[Stefan Assmann <sassmann@kpanic.de>]

On 27.04.2011 23:12, Andi Kleen wrote:
> On Wed, Apr 27, 2011 at 06:16:46PM +0200, Stefan Assmann wrote:
>> BadRAM is a mechanism to exclude memory addresses (pages) from being used by
>> the system. The addresses are given to the kernel via kernel command line.
>> This is useful for systems with defective RAM modules, especially if the RAM
>> modules cannot be replaced.
>>
>> command line parameter: badram=<addr>,<mask>[,...]
>>
>> Patterns for the command line parameter can be obtained by running Memtest86.
>> In Memtest86 press "c" for configuration, select "Error Report Mode" and
>> finally "BadRAM Patterns"
>>
>> This has already been done by Rick van Rein a long time ago but it never found
>> it's way into the kernel.
> 
> Looks good to me, except for the too verbose printks. Logging
> every page this way will be very noisy for larger areas.

You're right, logging every page marked would be too verbose. That's why
I wrapped that logging into pr_debug.
http://www.kernel.org/doc/local/pr_debug.txt
This way it shouldn't bother anybody but it still could be useful in the
case of debugging.
However I kept the printk in the case of early allocated pages. The user
should be notified of the attempt to mark a page that's already been
allocated by the kernel itself.

> 
> The mask will also only work for very simple memory interleaving
> setups, so I suspect it won't work for a lot of modern systems
> unless you go more fancy.
> 
> Longer term there should be also likely a better way to specify
> these pages than the kernel command line, e.g. the new persistent
> store on some systems.

I'd be happy to help improving and refining things for more fancy
scenarios after this is done.

Thanks for the feedback Andi.

  Stefan

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