Andi Kleen wrote:
On Tuesday 20 November 2007 04:50, Christoph Lameter wrote:
On Tue, 20 Nov 2007, Andi Kleen wrote:
I might be pointing out the obvious, but on x86-64 there is definitely
not 256TB of VM available for this.
Well maybe in the future.
That would either require more than 4 levels or larger pages
in page tables.
One of the issues that I ran into is that I had to place the cpu area
in between to make the offsets link right.
Above -2GB, otherwise you cannot address them
This limitation shouldn't apply to the percpu area, since gs_base can be
pointed anywhere in the address space -- in effect we're always indirect.
Obviously the offsets *within* the percpu area has to be in range (±2 GB
per cpu for absolute offsets, slightly smaller for %rip-based addressing
-- obviously judicious use of an offset for gs_base is essential in the
latter case).
Thus you want the percpu areas below -2 GB where they don't interfere
with modules or any other precious address space.
-hpa
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