This fixes Page Table accounting bug.
MIPS is the ONLY arch just defining __HAVE_ARCH_PMD_ALLOC_ONE alone.
Since commit 
b2b29d6d011944 (mm: account PMD tables like PTE tables),
"pmd_free" in asm-generic with PMD table accounting and "pmd_alloc_one"
in MIPS without PMD table accounting causes PageTable accounting number
negative, which read by global_zone_page_state(), always returns 0.
Signed-off-by: Huang Pei <huangpei@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
 
 static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
 {
-       pmd_t *pmd;
+       pmd_t *pmd = NULL;
+       struct page *pg;
 
-       pmd = (pmd_t *) __get_free_pages(GFP_KERNEL, PMD_ORDER);
-       if (pmd)
+       pg = alloc_pages(GFP_KERNEL | __GFP_ACCOUNT, PMD_ORDER);
+       if (pg) {
+               pgtable_pmd_page_ctor(pg);
+               pmd = (pmd_t *)page_address(pg);
                pmd_init((unsigned long)pmd, (unsigned long)invalid_pte_table);
+       }
        return pmd;
 }