On Fri, Jan 04, 2013 at 11:18:17PM -0600, Simon Jeons wrote:

quoted

+static int
+change_prot_numa_range(struct mm_struct *mm, struct vm_area_struct *vma,
+			unsigned long address)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte, *_pte;
+	struct page *page;
+	unsigned long _address, end;
+	spinlock_t *ptl;
+	int ret = 0;
+
+	VM_BUG_ON(address & ~PAGE_MASK);
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		goto out;
+
+	pud = pud_offset(pgd, address);
+	if (!pud_present(*pud))
+		goto out;
+
+	pmd = pmd_offset(pud, address);
+	if (pmd_none(*pmd))
+		goto out;
+
+	if (pmd_trans_huge_lock(pmd, vma) == 1) {
+		int page_nid;
+		ret = HPAGE_PMD_NR;
+
+		VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+
+		if (pmd_numa(*pmd)) {
+			spin_unlock(&mm->page_table_lock);
+			goto out;
+		}
+
+		page = pmd_page(*pmd);
+
+		/* only check non-shared pages */
+		if (page_mapcount(page) != 1) {
+			spin_unlock(&mm->page_table_lock);
+			goto out;
+		}
+
+		page_nid = page_to_nid(page);
+
+		if (pmd_numa(*pmd)) {
+			spin_unlock(&mm->page_table_lock);
+			goto out;
+		}
+

Hi Gorman,

Since pmd_trans_huge_lock has already held &mm->page_table_lock, then
why check pmd_numa(*pmd) again?

It looks like oversight. I've added a TODO item to clean it up when I
revisit NUMA balancing some time soon.

Thanks.

-- 
Mel Gorman
SUSE Labs

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