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    Subject[PATCH 3/5] mm: introduce PageHuge() for testing huge/gigantic pages
    Introduce PageHuge(), which identifies huge/gigantic pages
    by their dedicated compound destructor functions.

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    include/linux/mm.h | 24 ++++++++++++++++++++++++
    mm/hugetlb.c | 2 +-
    mm/page_alloc.c | 11 ++++++++++-
    3 files changed, 35 insertions(+), 2 deletions(-)

    --- mm.orig/mm/page_alloc.c
    +++ mm/mm/page_alloc.c
    @@ -299,13 +299,22 @@ void prep_compound_page(struct page *pag
    }

    #ifdef CONFIG_HUGETLBFS
    +/*
    + * This (duplicated) destructor function distinguishes gigantic pages from
    + * normal compound pages.
    + */
    +void free_gigantic_page(struct page *page)
    +{
    + __free_pages_ok(page, compound_order(page));
    +}
    +
    void prep_compound_gigantic_page(struct page *page, unsigned long order)
    {
    int i;
    int nr_pages = 1 << order;
    struct page *p = page + 1;

    - set_compound_page_dtor(page, free_compound_page);
    + set_compound_page_dtor(page, free_gigantic_page);
    set_compound_order(page, order);
    __SetPageHead(page);
    for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
    --- mm.orig/mm/hugetlb.c
    +++ mm/mm/hugetlb.c
    @@ -550,7 +550,7 @@ struct hstate *size_to_hstate(unsigned l
    return NULL;
    }

    -static void free_huge_page(struct page *page)
    +void free_huge_page(struct page *page)
    {
    /*
    * Can't pass hstate in here because it is called from the
    --- mm.orig/include/linux/mm.h
    +++ mm/include/linux/mm.h
    @@ -355,6 +355,30 @@ static inline void set_compound_order(st
    page[1].lru.prev = (void *)order;
    }

    +#ifdef CONFIG_HUGETLBFS
    +void free_huge_page(struct page *page);
    +void free_gigantic_page(struct page *page);
    +
    +static inline int PageHuge(struct page *page)
    +{
    + compound_page_dtor *dtor;
    +
    + if (!PageCompound(page))
    + return 0;
    +
    + page = compound_head(page);
    + dtor = get_compound_page_dtor(page);
    +
    + return dtor == free_huge_page ||
    + dtor == free_gigantic_page;
    +}
    +#else
    +static inline int PageHuge(struct page *page)
    +{
    + return 0;
    +}
    +#endif
    +
    /*
    * Multiple processes may "see" the same page. E.g. for untouched
    * mappings of /dev/null, all processes see the same page full of
    --



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