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    Subject[PATCH 03/12] mm: Methods for teaching filesystems about PG_swapcache pages
    Date
    In order to teach filesystems to handle swap cache pages, three new
    page functions are introduced:

    pgoff_t page_file_index(struct page *);
    loff_t page_file_offset(struct page *);
    struct address_space *page_file_mapping(struct page *);

    page_file_index() - gives the offset of this page in the file in
    PAGE_CACHE_SIZE blocks. Like page->index is for mapped pages, this
    function also gives the correct index for PG_swapcache pages.

    page_file_offset() - uses page_file_index(), so that it will give
    the expected result, even for PG_swapcache pages.

    page_file_mapping() - gives the mapping backing the actual page;
    that is for swap cache pages it will give swap_file->f_mapping.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    include/linux/mm.h | 25 +++++++++++++++++++++++++
    include/linux/pagemap.h | 5 +++++
    mm/swapfile.c | 19 +++++++++++++++++++
    3 files changed, 49 insertions(+)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index b36d08c..0c0301c 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -805,6 +805,17 @@ static inline void *page_rmapping(struct page *page)
    return (void *)((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
    }

    +extern struct address_space *__page_file_mapping(struct page *);
    +
    +static inline
    +struct address_space *page_file_mapping(struct page *page)
    +{
    + if (unlikely(PageSwapCache(page)))
    + return __page_file_mapping(page);
    +
    + return page->mapping;
    +}
    +
    static inline int PageAnon(struct page *page)
    {
    return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
    @@ -821,6 +832,20 @@ static inline pgoff_t page_index(struct page *page)
    return page->index;
    }

    +extern pgoff_t __page_file_index(struct page *page);
    +
    +/*
    + * Return the file index of the page. Regular pagecache pages use ->index
    + * whereas swapcache pages use swp_offset(->private)
    + */
    +static inline pgoff_t page_file_index(struct page *page)
    +{
    + if (unlikely(PageSwapCache(page)))
    + return __page_file_index(page);
    +
    + return page->index;
    +}
    +
    /*
    * Return true if this page is mapped into pagetables.
    */
    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index 7cfad3b..e42c762 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -286,6 +286,11 @@ static inline loff_t page_offset(struct page *page)
    return ((loff_t)page->index) << PAGE_CACHE_SHIFT;
    }

    +static inline loff_t page_file_offset(struct page *page)
    +{
    + return ((loff_t)page_file_index(page)) << PAGE_CACHE_SHIFT;
    +}
    +
    extern pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
    unsigned long address);

    diff --git a/mm/swapfile.c b/mm/swapfile.c
    index 71373d0..6123151 100644
    --- a/mm/swapfile.c
    +++ b/mm/swapfile.c
    @@ -33,6 +33,7 @@
    #include <linux/oom.h>
    #include <linux/frontswap.h>
    #include <linux/swapfile.h>
    +#include <linux/export.h>

    #include <asm/pgtable.h>
    #include <asm/tlbflush.h>
    @@ -2286,6 +2287,24 @@ int swapcache_prepare(swp_entry_t entry)
    }

    /*
    + * out-of-line __page_file_ methods to avoid include hell.
    + */
    +struct address_space *__page_file_mapping(struct page *page)
    +{
    + VM_BUG_ON(!PageSwapCache(page));
    + return page_swap_info(page)->swap_file->f_mapping;
    +}
    +EXPORT_SYMBOL_GPL(__page_file_mapping);
    +
    +pgoff_t __page_file_index(struct page *page)
    +{
    + swp_entry_t swap = { .val = page_private(page) };
    + VM_BUG_ON(!PageSwapCache(page));
    + return swp_offset(swap);
    +}
    +EXPORT_SYMBOL_GPL(__page_file_index);
    +
    +/*
    * add_swap_count_continuation - called when a swap count is duplicated
    * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
    * page of the original vmalloc'ed swap_map, to hold the continuation count
    --
    1.7.9.2


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