kernel ram testing

["Dr. David Alan Gilbert" <linux@spamtrap.treblig.org>]

Hi,
  After a particularly odd experience with a duff dimm a few weeks ago*  I
started thinking again about building continuous RAM testing into the kernel.

I've so far put together a little piece of code that regularly checksums
the kernel text (from _text to _etext).  But now I have some questions:

 1) _text and _etext seem to be defined differently on different
 architectures (some don't define both).  Ideally I think I'd like just
 the kernel text in a way that can be extracted with objdump at build
 time (so I can calculate the sum then for comparison). Suggestions on
 whether _text and _etext are appropriate would be useful.

 2) I want to test the rest of RAM as well - as much as possible,
 repeatedly while the system is running.  I could repeatedly allocate,
 test and deallocate a page. But will I keep getting the same page
 rather than circling through the rest of RAM? Can I ask for particular
 physical pages portably?

 3) I also want to test pages that are being used by the buffers and
 processes; I'd really like to kick a page onto a different physical
 page so I can test it - is this easily possible? (I could lock the
 whole machine down, copy the page somewhere else and then test it, but
 I fear this would take too long).


At the moment my code lives in a kernel thread (kintegrityd) that runs
and then sleeps for a while before running again (at lowest priority
above idle). (I'm presently fiddling with this under user mode linux
2.4.18).

Thoughts and suggestions welcome.

Dave

(*) The DIMM appears, from memtest86, to have had an approximately 4MB
range where one bit in 32bits (or was it perhaps wider) was stuck low.
First noticed by a mismatch on md5sums of a downloaded debian package
and by ' characters appearing in an od I did of the corrupted package on
a machine that otherwise appeared stable.

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