Re: [RFC] Tight check of pfn_valid on sparsemem

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Wed, 2010-07-14 at 00:43 +0900, Minchan Kim wrote:
> 3 is not a big deal than 2 about memory usage.
> If the system use memory space fully(MAX_PHYSMEM_BITS 31), it just consumes
> 1024(128 * 8) byte. So now I think best solution is 2. 
> 
> Russell. What do you think about it? 

I'm not Russell, but I'll tell you what I think. :)

Make the sections 16MB.  You suggestion to add the start/end pfns
_doubles_ the size of the structure, and its size overhead.  We have
systems with a pretty tremendous amount of memory with 16MB sections.

If you _really_ can't make the section size smaller, and the vast
majority of the sections are fully populated, you could hack something
in.  We could, for instance, have a global list that's mostly readonly
which tells you which sections need to be have their sizes closely
inspected.  That would work OK if, for instance, you only needed to
check a couple of memory sections in the system.  It'll start to suck if
you made the lists very long.

-- Dave

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