Re: [PATCH v5 07/11] thp: implement splitting pmd for huge zero page

Kirill A. Shutemov
2012-11-15T09:23:48Z

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On Wed, Nov 14, 2012 at 03:28:15PM -0800, David Rientjes wrote:
> On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:
>
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 90e651c..f36bc7d 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1611,6 +1611,7 @@ int split_huge_page(struct page *page)
> > struct anon_vma *anon_vma;
> > int ret = 1;
> >
> > + BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
> > BUG_ON(!PageAnon(page));
> > anon_vma = page_lock_anon_vma(page);
> > if (!anon_vma)
> > @@ -2509,23 +2510,63 @@ static int khugepaged(void *none)
> > return 0;
> > }
> >
> > +static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
> > + unsigned long haddr, pmd_t *pmd)
> > +{
>
> This entire function duplicates other code in mm/huge_memory.c which gives
> even more incentive into breaking do_huge_pmd_wp_zero_page_fallback() into
> logical helper functions and reusing them for both page and !page.
> Duplicating all this code throughout the thp code just becomes a
> maintenance nightmare down the road.

Okay, I'll try.

> > + pgtable_t pgtable;
> > + pmd_t _pmd;
> > + int i;
> > +
> > + pmdp_clear_flush(vma, haddr, pmd);
> > + /* leave pmd empty until pte is filled */
> > +
> > + pgtable = get_pmd_huge_pte(vma->vm_mm);
> > + pmd_populate(vma->vm_mm, &_pmd, pgtable);
> > +
> > + for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> > + pte_t *pte, entry;
> > + entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
> > + entry = pte_mkspecial(entry);
> > + pte = pte_offset_map(&_pmd, haddr);
> > + VM_BUG_ON(!pte_none(*pte));
> > + set_pte_at(vma->vm_mm, haddr, pte, entry);
> > + pte_unmap(pte);
> > + }
> > + smp_wmb(); /* make pte visible before pmd */
> > + pmd_populate(vma->vm_mm, pmd, pgtable);
> > +}
> > +
> > void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
> > pmd_t *pmd)
> > {
> > struct page *page;
> > + struct mm_struct *mm = vma->vm_mm;
> > unsigned long haddr = address & HPAGE_PMD_MASK;
> > + unsigned long mmun_start; /* For mmu_notifiers */
> > + unsigned long mmun_end; /* For mmu_notifiers */
> >
> > BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
> >
> > - spin_lock(&vma->vm_mm->page_table_lock);
> > + mmun_start = haddr;
> > + mmun_end = address + HPAGE_PMD_SIZE;
>
> address or haddr?

haddr. I'll fix.

--
Kirill A. Shutemov

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