Re: hammer: MAP_32BIT

[Timothy Miller]

H. Peter Anvin wrote:
> Timothy Miller wrote:
> 
>>If your program is capable of handling an address with more than 32
>>bits, what point is there giving a hint?  Either your program can handle
>>64-bit pointers or it cannot.  Any program flexible enough to handle
>>either size dynamically would expend enough overhead checking that it
>>would be worse than if it just made a hard choice.
>>
> 
> 
> The purpose is that there is a slight task-switching speed advantage if
> the address is in the bottom 4 GB.  Since this affects every process,
> and most processes use very little TLS, this is worthwhile.
> 
> This is fundamentally due to a K8 design flaw.

Is there an explicit check somewhere for this?  Are the page tables laid 
out differently?