Messages in this thread Patch in this message | | | Date | Wed, 11 Apr 2007 22:30:47 -0700 | Subject | [PATCH 2/4] Pte clear optimization.patch | From | Zachary Amsden <> |
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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 <zach@vmware.com>
diff -r 1478ce4ec9e3 include/asm-i386/pgtable-2level.h --- a/include/asm-i386/pgtable-2level.h Wed Apr 11 17:13:10 2007 -0700 +++ b/include/asm-i386/pgtable-2level.h Wed Apr 11 18:22:51 2007 -0700 @@ -35,6 +35,11 @@ static inline void native_set_pmd(pmd_t #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) { diff -r 1478ce4ec9e3 include/asm-i386/pgtable.h --- a/include/asm-i386/pgtable.h Wed Apr 11 17:13:10 2007 -0700 +++ b/include/asm-i386/pgtable.h Wed Apr 11 18:21:43 2007 -0700 @@ -349,7 +349,7 @@ static inline pte_t ptep_get_and_clear_f 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); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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