From c2c1accd4b2f9c82fb89d40611c7f581948db255 Mon Sep 17 00:00:00 2001 From: Zachary Amsden Date: Wed, 2 May 2007 19:27:19 +0200 Subject: [PATCH] [PATCH] i386: pte clear optimization When exiting from an address space, no special hypervisor notification of page table updates needs to occur; direct page table hypervisors, such as Xen, switch to another address space first (init_mm) and unprotects the page tables to avoid the cost of trapping to the hypervisor for each pte_clear. Shadow mode hypervisors, such as VMI and lhype don't need to do the extra work of calling through paravirt-ops, and can just directly clear the page table entries without notifiying the hypervisor, since all the page tables are about to be freed. So introduce native_pte_clear functions which bypass any paravirt-ops notification. This results in a significant performance win for VMI and removes some indirect calls from zap_pte_range. Note the 3-level paging already had a native_pte_clear function, thus demanding argument conformance and extra args for the 2-level definition. Signed-off-by: Zachary Amsden Signed-off-by: Andrew Morton Signed-off-by: Andi Kleen --- include/asm-i386/pgtable-2level.h | 5 +++++ include/asm-i386/pgtable.h | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/include/asm-i386/pgtable-2level.h b/include/asm-i386/pgtable-2level.h index 781fe4bcc962..85d9005c0cdf 100644 --- a/include/asm-i386/pgtable-2level.h +++ b/include/asm-i386/pgtable-2level.h @@ -36,6 +36,11 @@ static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd) #define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0) #define pmd_clear(xp) do { set_pmd(xp, __pmd(0)); } while (0) +static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *xp) +{ + *xp = __pte(0); +} + static inline pte_t native_ptep_get_and_clear(pte_t *xp) { return __pte(xchg(&xp->pte_low, 0)); diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h index e7ddd2341309..00e97a9d367e 100644 --- a/include/asm-i386/pgtable.h +++ b/include/asm-i386/pgtable.h @@ -344,7 +344,7 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm, unsigned long pte_t pte; if (full) { pte = *ptep; - pte_clear(mm, addr, ptep); + native_pte_clear(mm, addr, ptep); } else { pte = ptep_get_and_clear(mm, addr, ptep); }