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[PATCH] i386: pte clear optimization

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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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Zachary Amsden 2007-05-02 19:27:19 +02:00 committed by Andi Kleen
parent df3624aa29
commit c2c1accd4b
2 changed files with 6 additions and 1 deletions
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5
include/asm-i386/pgtable-2level.h
View File

@ -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));

2
include/asm-i386/pgtable.h
View File

@ -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);
}