From edd6bcd8209c31b91e1fbc112a756475091c483d Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Mon, 4 Feb 2008 16:48:02 +0100 Subject: [PATCH] x86: pud_clear: only reload cr3 if necessary Rather than unconditionally reloading cr3, only do so if the pud we're updating is within the active pgd. This eliminates TLB flushes most of the time. The performance-critical uses of pud_clear are during execve and exit, but in those cases cr3 is referring to some other pagetable. The only other use of pud_clear is during a large (1Gbyte+) munmap, and those are sufficiently rare that a couple of cr3 reloads won't hurt. Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- include/asm-x86/pgtable-3level.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/include/asm-x86/pgtable-3level.h b/include/asm-x86/pgtable-3level.h index ed4c6f0..ad71960 100644 --- a/include/asm-x86/pgtable-3level.h +++ b/include/asm-x86/pgtable-3level.h @@ -93,17 +93,20 @@ static inline void native_pmd_clear(pmd_t *pmd) static inline void pud_clear(pud_t *pudp) { + unsigned long pgd; + set_pud(pudp, __pud(0)); /* * Pentium-II erratum A13: in PAE mode we explicitly have to flush * the TLB via cr3 if the top-level pgd is changed... * - * XXX I don't think we need to worry about this here, since - * when clearing the pud, the calling code needs to flush the - * tlb anyway. But do it now for safety's sake. - jsgf + * Make sure the pud entry we're updating is within the + * current pgd to avoid unnecessary TLB flushes. */ - write_cr3(read_cr3()); + pgd = read_cr3(); + if (__pa(pudp) >= pgd && __pa(pudp) < (pgd + sizeof(pgd_t)*PTRS_PER_PGD)) + write_cr3(pgd); } #define pud_page(pud) \ -- 2.7.4