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SubjectRe: [PATCH] x86/mm: Don't flush the TLB on #WP pmd fixups
On Tue, 20 Nov 2012, Ingo Molnar wrote:

> Subject: x86/mm: Don't flush the TLB on #WP pmd fixups
> From: Ingo Molnar <mingo@kernel.org>
> Date: Tue Nov 20 14:46:34 CET 2012
>
> If we have a write protection #PF and fix up the pmd then the
> hugetlb code [the only user of pmdp_set_access_flags], in its
> do_huge_pmd_wp_page() page fault resolution function calls
> pmdp_set_access_flags() to mark the pmd permissive again,
> and flushes the TLB.
>
> This TLB flush is unnecessary: a flush on #PF is guaranteed on
> most (all?) x86 CPUs, and even in the worst-case we'll generate
> a spurious fault.
>
> So remove it.
>

This patch did not cause the 2% speedup that you reported with THP
enabled for me:

numa/core at ec05a2311c35: 136918.34 SPECjbb2005 bops
numa/core at 01aa90068b12: 128315.19 SPECjbb2005 bops (-6.3%)
numa/core at 01aa90068b12 + patch: 128184.77 SPECjbb2005 bops (-6.4%)


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