Re: [discuss] Re: [patch 3/3] add x86-64 support for memory hot-add II

[Andi Kleen]

> In general SRAT has a hotplug memory bit so it's possible
> to predict how much memory there will be in advance. Since
> the overhead of the kernel page tables should be very
> low I would prefer if you just used instead.
> 
> (i.e. instead of extending the kernel mapping preallocate
> the direct mapping and just clear the P bits) 
> 
> That should be much simpler.

Looking at it again - accessing SRAT currently relies on the 
direct mapping already. Untangling that would be possible,
but require an bt_ioremap which would also add lots of code.

Ok I retract that objection. I guess your way is better
for now.

In addition to the __cpuinit comment

+if (after_bootmem) spin_unlock(&init_mm.page_table_lock);

Conditional locking is evil. spinlocking in the boot
case should just work too I think.

The EXPORTs should be probably EXPORT_SYMBOL_GPL.

With these changes it would look ok for me.

-Andi
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