Re: Overhead of highpte

From: William Lee Irwin III (
Date: Wed Jul 02 2003 - 18:15:02 EST

On Wed, Jul 02, 2003 at 03:53:24PM -0700, Martin J. Bligh wrote:
> Some people were saying they couldn't see an overhead with highpte.
> Seems pretty obvious to me still. It should help *more* on the NUMA
> box, as PTEs become node-local.
> The kmap_atomic is, of course, perfectly understandable. The increase
> in the rmap functions is a bit of a mystery to me.

The rmap functions perform kmap_atomic() internally while traversing
pte_chains and so will take various additional TLB misses and incur
various bits of computational expense with i386's kmap_atomic() semantics.

The observations I made were in combination with both highpmd and an as
of yet unmerged full 3-level pagetable cacheing patch.

-- wli
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