Re: [PATCH] Get rid of zone_table

[Andy Whitcroft <apw@shadowen.org>]

Dave Hansen wrote:
> Now that I think about it, we should have room to encode that thing
> inside of the section number on 32-bit platforms.
> 
> We have 32-bits of space, and we need to encode a number that is a
> maximum of 4 bits in size.  That leaves 28 bits minus the one that we
> use for the section present bit.  Our minimum section size on x86 is
> something like 64 or 128MB.  Let's say 64MB.  So, on a 64GB system, we
> only need 1k sections, and 10 bits.
> 
> So, the node number would almost certainly fit in the existing
> mem_section.  We'd just need to set it and mask it out.  
> 
> Andy, what do you think?

The flags field only has a 9 bit space for these value fields.  Into
which we normally shove NODE,ZONE.  With SPARSEMEM that is SECTION,ZONE
and so there is only room for 6-7 bits of information in this field.

The section table only contains an adjusted pointer to the mem_map for
that section?  We use the bottom two bits of that pointer for a couple
of flags.  I don't think there is any space in it.

Are you thinking of somewhere else?

-apw

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