[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 <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h
index e7ddd23..00e97a9 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);
 	}