Re: how to tell if arbitrary kernel memory address is backed by physicalmemory?

[Chris Friesen]

Christoph Lameter wrote:
> On Thu, 16 Apr 2009, Chris Friesen wrote:

> > Is there a portable way to tell whether a particular virtual address in the
> > lowmem address range is backed by physical memory and is readable?
> >
> > For background...we have some guys working on a software memory scrubber for
> > an embedded board.  The memory controller supports ECC but doesn't support
> > scrubbing  in hardware.  What we want to do is walk all of lowmem, reading in
> > memory.  If a fault is encountered, it will be handled by other code.
>
> Virtual address in the lowmem address range? lowmem address ranges exist
> for physical addresses.
>
> If you walk lowmem (physical) then you will never see a missing page.

We have a mips board that appears to have holes in the lowmem mappings 
such that blindly walking all of it causes problems.  I assume the 
allocator knows about these holes and simply doesn't assign memory at 
those addresses.

We may have found a solution though...it looks like virt_addr_valid() 
returns false for the problematic addresses.  Would it be reasonable to 
call this once for each page before trying to access it?

Chris

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