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    Subject[PATCHv4 08/24] mm: adjust FOLL_SPLIT for new refcounting
    Date
    We prepare kernel to allow transhuge pages to be mapped with ptes too.
    We need to handle FOLL_SPLIT in follow_page_pte().

    Also we use split_huge_page() directly instead of split_huge_page_pmd().
    split_huge_page_pmd() will gone.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    mm/gup.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++------------------
    1 file changed, 51 insertions(+), 19 deletions(-)

    diff --git a/mm/gup.c b/mm/gup.c
    index ca7b607ab671..080535d5efab 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -79,6 +79,20 @@ retry:
    page = pte_page(pte);
    }

    + if (flags & FOLL_SPLIT && PageTransCompound(page)) {
    + int ret;
    + page = compound_head(page);
    + get_page(page);
    + pte_unmap_unlock(ptep, ptl);
    + lock_page(page);
    + ret = split_huge_page(page);
    + unlock_page(page);
    + put_page(page);
    + if (ret)
    + return ERR_PTR(ret);
    + goto retry;
    + }
    +
    if (flags & FOLL_GET)
    get_page_foll(page);
    if (flags & FOLL_TOUCH) {
    @@ -186,27 +200,45 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
    }
    if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
    return no_page_table(vma, flags);
    - if (pmd_trans_huge(*pmd)) {
    - if (flags & FOLL_SPLIT) {
    - split_huge_page_pmd(vma, address, pmd);
    - return follow_page_pte(vma, address, pmd, flags);
    - }
    - ptl = pmd_lock(mm, pmd);
    - if (likely(pmd_trans_huge(*pmd))) {
    - if (unlikely(pmd_trans_splitting(*pmd))) {
    - spin_unlock(ptl);
    - wait_split_huge_page(vma->anon_vma, pmd);
    - } else {
    - page = follow_trans_huge_pmd(vma, address,
    - pmd, flags);
    - spin_unlock(ptl);
    - *page_mask = HPAGE_PMD_NR - 1;
    - return page;
    - }
    - } else
    + if (likely(!pmd_trans_huge(*pmd)))
    + return follow_page_pte(vma, address, pmd, flags);
    +
    + ptl = pmd_lock(mm, pmd);
    + if (unlikely(!pmd_trans_huge(*pmd))) {
    + spin_unlock(ptl);
    + return follow_page_pte(vma, address, pmd, flags);
    + }
    +
    + if (unlikely(pmd_trans_splitting(*pmd))) {
    + spin_unlock(ptl);
    + wait_split_huge_page(vma->anon_vma, pmd);
    + return follow_page_pte(vma, address, pmd, flags);
    + }
    +
    + if (flags & FOLL_SPLIT) {
    + int ret;
    + page = pmd_page(*pmd);
    + if (is_huge_zero_page(page)) {
    + spin_unlock(ptl);
    + ret = 0;
    + split_huge_pmd(vma, pmd, address);
    + } else {
    + get_page(page);
    spin_unlock(ptl);
    + lock_page(page);
    + ret = split_huge_page(page);
    + unlock_page(page);
    + put_page(page);
    + }
    +
    + return ret ? ERR_PTR(ret) :
    + follow_page_pte(vma, address, pmd, flags);
    }
    - return follow_page_pte(vma, address, pmd, flags);
    +
    + page = follow_trans_huge_pmd(vma, address, pmd, flags);
    + spin_unlock(ptl);
    + *page_mask = HPAGE_PMD_NR - 1;
    + return page;
    }

    static int get_gate_page(struct mm_struct *mm, unsigned long address,
    --
    2.1.4


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