Hi,
On Mon, 07 Dec 1998 18:56:49 -0600, Tim Majni <[EMAIL PROTECTED]> said:
> There is a reason why they call it IA-32. The 36 bit stuff is an
> afterthought. There are significant limitations on memory above 4GB,
> least of which being 4MB pages.
Not if you are using 3-level page tables. The memory above 4G is truly
transparent to the application in that case.
> How about IO out of that region? Difficult to say the least.
IO bounce buffers (already needed for ISA DMA transfers) or 64-bit PCI.
You also do tricks like allocating page cache pages from the bottom of
memory up and anonymous pages from the top down, to reduce the
likelihood of having to do IO above 4G.
> Addressing more than 4GB of memory by an application transparently is
> also difficult.
Not with 3-level page tables. The memory above 4G looks *exactly* the
same as memory below the boundary. With 3-level page tables, all of the
application's 4k pages have 36 bit physical addresses (in fact there is
room in the page tables for much more addressing than that: using
3-level page tables gives you 64-bit ptes).
--Stephen
-
Linux SMP list: FIRST see FAQ at http://www.irisa.fr/prive/mentre/smp-faq/
To Unsubscribe: send "unsubscribe linux-smp" to [EMAIL PROTECTED]
