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SubjectRe: [PATCH v3 07/10] thp: implement splitting pmd for huge zero page
On 10/02/2012 11:19 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> We can't split huge zero page itself, but we can split the pmd which
> points to it.
>
> On splitting the pmd we create a table with all ptes set to normal zero
> page.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
> mm/huge_memory.c | 32 ++++++++++++++++++++++++++++++++
> 1 files changed, 32 insertions(+), 0 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 95032d3..3f1c59c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1600,6 +1600,7 @@ 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)
> @@ -2503,6 +2504,32 @@ 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)
> +{
> + pgtable_t pgtable;
> + pmd_t _pmd;
> + int i;
> +
> + pmdp_clear_flush_notify(vma, haddr, pmd);

why I can't find function pmdp_clear_flush_notify in kernel source code?
Do you mean pmdp_clear_flush_young_notify or something like that?

> + /* 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)
> {
> @@ -2516,6 +2543,11 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
> spin_unlock(&vma->vm_mm->page_table_lock);
> return;
> }
> + if (is_huge_zero_pmd(*pmd)) {
> + __split_huge_zero_page_pmd(vma, haddr, pmd);
> + spin_unlock(&vma->vm_mm->page_table_lock);
> + return;
> + }
> page = pmd_page(*pmd);
> VM_BUG_ON(!page_count(page));
> get_page(page);



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