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    Subject[PATCHv2, RFC 02/30] mm: implement zero_huge_user_segment and friends
    Date
    From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

    Let's add helpers to clear huge page segment(s). They provide the same
    functionallity as zero_user_segment{,s} and zero_user, but for huge
    pages.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    include/linux/mm.h | 15 +++++++++++++++
    mm/memory.c | 26 ++++++++++++++++++++++++++
    2 files changed, 41 insertions(+)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 5b7fd4e..df83ab9 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1731,6 +1731,21 @@ extern void dump_page(struct page *page);
    extern void clear_huge_page(struct page *page,
    unsigned long addr,
    unsigned int pages_per_huge_page);
    +extern void zero_huge_user_segment(struct page *page,
    + unsigned start, unsigned end);
    +static inline void zero_huge_user_segments(struct page *page,
    + unsigned start1, unsigned end1,
    + unsigned start2, unsigned end2)
    +{
    + zero_huge_user_segment(page, start1, end1);
    + zero_huge_user_segment(page, start2, end2);
    +}
    +static inline void zero_huge_user(struct page *page,
    + unsigned start, unsigned len)
    +{
    + zero_huge_user_segment(page, start, start+len);
    +}
    +
    extern void copy_user_huge_page(struct page *dst, struct page *src,
    unsigned long addr, struct vm_area_struct *vma,
    unsigned int pages_per_huge_page);
    diff --git a/mm/memory.c b/mm/memory.c
    index 494526a..98c25dd 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -4213,6 +4213,32 @@ void clear_huge_page(struct page *page,
    }
    }

    +void zero_huge_user_segment(struct page *page, unsigned start, unsigned end)
    +{
    + int i;
    +
    + BUG_ON(end < start);
    +
    + might_sleep();
    +
    + if (start == end)
    + return;
    +
    + /* start and end are on the same small page */
    + if ((start & PAGE_MASK) == ((end - 1) & PAGE_MASK))
    + return zero_user_segment(page + (start >> PAGE_SHIFT),
    + start & ~PAGE_MASK,
    + ((end - 1) & ~PAGE_MASK) + 1);
    +
    + zero_user_segment(page + (start >> PAGE_SHIFT),
    + start & ~PAGE_MASK, PAGE_SIZE);
    + for (i = (start >> PAGE_SHIFT) + 1; i < (end >> PAGE_SHIFT) - 1; i++) {
    + cond_resched();
    + clear_highpage(page + i);
    + }
    + zero_user_segment(page + i, 0, ((end - 1) & ~PAGE_MASK) + 1);
    +}
    +
    static void copy_user_gigantic_page(struct page *dst, struct page *src,
    unsigned long addr,
    struct vm_area_struct *vma,
    --
    1.7.10.4


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