Re: mlockall and mmap of IO devices don't mix

[Andrew Morton]

Andi Kleen <ak@xxxxxx> wrote:
>
> Joe Korty <joe.korty@xxxxxxxx> writes:
> 
> >  
> > I do not believe that the above constitutes a correct fix.  The
> > problem is that follow_pages() is fundamentally not able to handle a
> > mapping which does not have a 'struct page' backing it up, and a
> > mapping to IO memory by definition has no 'struct page' structure to
> > back it up.
> 
> The 2.4 vm scanner handles this by always checking VALID_PAGE().
> 

VALID_PAGE got nuked.

It still exists in vestigial form in some architectures, but x86 does not
implement it and core kernel does not use it.

It is not a trivial thing to do now we no longer have a single mem_map[].
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