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

[Tolentino, Matthew E]

Andi Kleen <mailto:ak@xxxxxxx> wrote:
>> 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.

Thanks for considering this Andi.  
 
> 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.

Excellent points.  Thanks for the review and suggestions.  I'm
testing a revised patch now and will repost in a bit.  

matt
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