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SubjectRe: [PATCHv4 19/24] thp, mm: use migration entries to freeze page counts on split
On Mon, Mar 30, 2015 at 09:15:47PM +0530, Aneesh Kumar K.V wrote:
> "Kirill A. Shutemov" <kirill@shutemov.name> writes:
>
> > On Mon, Mar 30, 2015 at 08:38:08PM +0530, Aneesh Kumar K.V wrote:
> >> ....
> >> ....
> >> +static void freeze_page(struct anon_vma *anon_vma, struct page *page)
> >> > +{
> >> > + struct anon_vma_chain *avc;
> >> > + struct vm_area_struct *vma;
> >> > + pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> >>
> >> So this get called only with head page, We also do
> >> BUG_ON(PageTail(page)) in the caller. But
> >>
> >>
> >> > + unsigned long addr, haddr;
> >> > + unsigned long mmun_start, mmun_end;
> >> > + pgd_t *pgd;
> >> > + pud_t *pud;
> >> > + pmd_t *pmd;
> >> > + pte_t *start_pte, *pte;
> >> > + spinlock_t *ptl;
> >> ......
> >>
> >>
> >> > +
> >> > +static void unfreeze_page(struct anon_vma *anon_vma, struct page *page)
> >> > +{
> >> > + struct anon_vma_chain *avc;
> >> > + pgoff_t pgoff = page_to_pgoff(page);
> >>
> >> Why ? Can this get called for tail pages ?
> >
> > It cannot. pgoff is offset of head page (and therefore whole compound
> > page) within rmapping.
> >
>
> This we can use
>
> pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
>
> similar to what we do in freeze_page(). The difference between
> freeze/unfreeze confused me.

Fair enough. Will fix.

--
Kirill A. Shutemov


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