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    Subject[PATCHv5 17/36] fs: make block_read_full_page() be able to read huge page
    Date
    The approach is straight-forward: for compound pages we read out whole
    huge page.

    For huge page we cannot have array of buffer head pointers on stack --
    it's 4096 pointers on x86-64 -- 'arr' is allocated with kmalloc() for
    huge pages.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    fs/buffer.c | 22 +++++++++++++++++-----
    include/linux/buffer_head.h | 9 +++++----
    include/linux/page-flags.h | 2 +-
    3 files changed, 23 insertions(+), 10 deletions(-)

    diff --git a/fs/buffer.c b/fs/buffer.c
    index d21771fcf7d3..090f7edfa6b7 100644
    --- a/fs/buffer.c
    +++ b/fs/buffer.c
    @@ -871,7 +871,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,

    try_again:
    head = NULL;
    - offset = PAGE_SIZE;
    + offset = hpage_size(page);
    while ((offset -= size) >= 0) {
    bh = alloc_buffer_head(GFP_NOFS);
    if (!bh)
    @@ -1466,7 +1466,7 @@ void set_bh_page(struct buffer_head *bh,
    struct page *page, unsigned long offset)
    {
    bh->b_page = page;
    - BUG_ON(offset >= PAGE_SIZE);
    + BUG_ON(offset >= hpage_size(page));
    if (PageHighMem(page))
    /*
    * This catches illegal uses and preserves the offset:
    @@ -2280,11 +2280,13 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
    {
    struct inode *inode = page->mapping->host;
    sector_t iblock, lblock;
    - struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
    + struct buffer_head *arr_on_stack[MAX_BUF_PER_PAGE];
    + struct buffer_head *bh, *head, **arr = arr_on_stack;
    unsigned int blocksize, bbits;
    int nr, i;
    int fully_mapped = 1;

    + VM_BUG_ON_PAGE(PageTail(page), page);
    head = create_page_buffers(page, inode, 0);
    blocksize = head->b_size;
    bbits = block_size_bits(blocksize);
    @@ -2295,6 +2297,11 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
    nr = 0;
    i = 0;

    + if (PageTransHuge(page)) {
    + arr = kmalloc(sizeof(struct buffer_head *) * HPAGE_PMD_NR *
    + MAX_BUF_PER_PAGE, GFP_NOFS);
    + }
    +
    do {
    if (buffer_uptodate(bh))
    continue;
    @@ -2310,7 +2317,9 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
    SetPageError(page);
    }
    if (!buffer_mapped(bh)) {
    - zero_user(page, i * blocksize, blocksize);
    + zero_user(page + (i * blocksize / PAGE_SIZE),
    + i * blocksize % PAGE_SIZE,
    + blocksize);
    if (!err)
    set_buffer_uptodate(bh);
    continue;
    @@ -2336,7 +2345,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
    if (!PageError(page))
    SetPageUptodate(page);
    unlock_page(page);
    - return 0;
    + goto out;
    }

    /* Stage two: lock the buffers */
    @@ -2358,6 +2367,9 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
    else
    submit_bh(REQ_OP_READ, 0, bh);
    }
    +out:
    + if (arr != arr_on_stack)
    + kfree(arr);
    return 0;
    }
    EXPORT_SYMBOL(block_read_full_page);
    diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
    index fd4134ce9c54..f12f6293ed44 100644
    --- a/include/linux/buffer_head.h
    +++ b/include/linux/buffer_head.h
    @@ -131,13 +131,14 @@ BUFFER_FNS(Meta, meta)
    BUFFER_FNS(Prio, prio)
    BUFFER_FNS(Defer_Completion, defer_completion)

    -#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
    +#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~hpage_mask(bh->b_page))

    /* If we *know* page->private refers to buffer_heads */
    -#define page_buffers(page) \
    +#define page_buffers(__page) \
    ({ \
    - BUG_ON(!PagePrivate(page)); \
    - ((struct buffer_head *)page_private(page)); \
    + struct page *p = compound_head(__page); \
    + BUG_ON(!PagePrivate(p)); \
    + ((struct buffer_head *)page_private(p)); \
    })
    #define page_has_buffers(page) PagePrivate(page)

    diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
    index a2bef9a41bcf..20b7684e9298 100644
    --- a/include/linux/page-flags.h
    +++ b/include/linux/page-flags.h
    @@ -730,7 +730,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
    */
    static inline int page_has_private(struct page *page)
    {
    - return !!(page->flags & PAGE_FLAGS_PRIVATE);
    + return !!(compound_head(page)->flags & PAGE_FLAGS_PRIVATE);
    }

    #undef PF_ANY
    --
    2.10.2
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