Re: [PATCH 22/49] mm: mempolicy: Add MPOL_MF_LAZY

[Mel Gorman]

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