[PATCH] optimise copy page range

Suggested by Linus: optimise a condition in the clear_p?d_range functions.
Results in one less conditional branch on i386 with gcc-3.4.4
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -98,7 +98,8 @@ static inline void clear_pmd_range(struct mmu_gather *tlb, pmd_t *pmd, unsigned
 		pmd_clear(pmd);
 		return;
 	}
-	if (!(start & ~PMD_MASK) && !(end & ~PMD_MASK)) {
+	if (!((start | end) & ~PMD_MASK)) {
+		/* Only clear full, aligned ranges */
 		page = pmd_page(*pmd);
 		pmd_clear(pmd);
 		dec_page_state(nr_page_table_pages);
@@ -131,7 +132,8 @@ static inline void clear_pud_range(struct mmu_gather *tlb, pud_t *pud, unsigned
 		addr = next;
 	} while (addr && (addr < end));
 
-	if (!(start & ~PUD_MASK) && !(end & ~PUD_MASK)) {
+	if (!((start | end) & ~PUD_MASK)) {
+		/* Only clear full, aligned ranges */
 		pud_clear(pud);
 		pmd_free_tlb(tlb, __pmd);
 	}
@@ -162,7 +164,8 @@ static inline void clear_pgd_range(struct mmu_gather *tlb, pgd_t *pgd, unsigned
 		addr = next;
 	} while (addr && (addr < end));
 
-	if (!(start & ~PGDIR_MASK) && !(end & ~PGDIR_MASK)) {
+	if (!((start | end) & ~PGDIR_MASK)) {
+		/* Only clear full, aligned ranges */
 		pgd_clear(pgd);
 		pud_free_tlb(tlb, __pud);
 	}