On Fri, Feb 18, 2000 at 04:06:55PM -0800, Matthew Dillon wrote:
> If I understand the hardware hash table method correctly, then
> I think the absolute best choice for FreeBSD is to use that method
> as it will allow us to get rid of the scaleability problems we have
> with the pv_entry_t scheme we use for IA32. The number of pv_entry_t's
> in an IA64 architecture wind up being fixed. How big can we make the
> hardware-assisted hash table?
Smaller than 2**64. Minimum is 2**15.
>
> Also, a hash table scheme is a much better fit for a 64 bit address
> space model, especially with sparse mappings. The MIPS R4K and later
> all use a hash table scheme and it seems to work well for them.
>
Madhu Talluri's paper on page tables for 64 bit address spaces claims that
having collision chains is expensive - for 8 bytes of mapping information,
the pointer and tag storage overhead is 16 bytes.
Though page table space is important, in the age of big memory computers,
I think performance and manageability are more important.
-Arun
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