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    Subject[PATCHv2 29/41] ext4: make ext4_mpage_readpages() hugepage-aware
    Date
    This patch modifies ext4_mpage_readpages() to deal with huge pages.

    We read out 2M at once, so we have to alloc (HPAGE_PMD_NR *
    blocks_per_page) sector_t for that. I'm not entirely happy with kmalloc
    in this codepath, but don't see any other option.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    fs/ext4/readpage.c | 38 ++++++++++++++++++++++++++++++++------
    1 file changed, 32 insertions(+), 6 deletions(-)

    diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
    index a81b829d56de..6d7cbddceeb2 100644
    --- a/fs/ext4/readpage.c
    +++ b/fs/ext4/readpage.c
    @@ -104,12 +104,12 @@ int ext4_mpage_readpages(struct address_space *mapping,

    struct inode *inode = mapping->host;
    const unsigned blkbits = inode->i_blkbits;
    - const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
    const unsigned blocksize = 1 << blkbits;
    sector_t block_in_file;
    sector_t last_block;
    sector_t last_block_in_file;
    - sector_t blocks[MAX_BUF_PER_PAGE];
    + sector_t blocks_on_stack[MAX_BUF_PER_PAGE];
    + sector_t *blocks = blocks_on_stack;
    unsigned page_block;
    struct block_device *bdev = inode->i_sb->s_bdev;
    int length;
    @@ -122,8 +122,9 @@ int ext4_mpage_readpages(struct address_space *mapping,
    map.m_flags = 0;

    for (; nr_pages; nr_pages--) {
    - int fully_mapped = 1;
    - unsigned first_hole = blocks_per_page;
    + int fully_mapped = 1, nr = nr_pages;
    + unsigned blocks_per_page = PAGE_SIZE >> blkbits;
    + unsigned first_hole;

    prefetchw(&page->flags);
    if (pages) {
    @@ -138,10 +139,31 @@ int ext4_mpage_readpages(struct address_space *mapping,
    goto confused;

    block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
    - last_block = block_in_file + nr_pages * blocks_per_page;
    +
    + if (PageTransHuge(page)) {
    + BUILD_BUG_ON(BIO_MAX_PAGES < HPAGE_PMD_NR);
    + nr = HPAGE_PMD_NR * blocks_per_page;
    + /* XXX: need a better solution ? */
    + blocks = kmalloc(sizeof(sector_t) * nr, GFP_NOFS);
    + if (!blocks) {
    + if (pages) {
    + delete_from_page_cache(page);
    + goto next_page;
    + }
    + return -ENOMEM;
    + }
    +
    + blocks_per_page *= HPAGE_PMD_NR;
    + last_block = block_in_file + blocks_per_page;
    + } else {
    + blocks = blocks_on_stack;
    + last_block = block_in_file + nr * blocks_per_page;
    + }
    +
    last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
    if (last_block > last_block_in_file)
    last_block = last_block_in_file;
    + first_hole = blocks_per_page;
    page_block = 0;

    /*
    @@ -213,6 +235,8 @@ int ext4_mpage_readpages(struct address_space *mapping,
    }
    }
    if (first_hole != blocks_per_page) {
    + if (PageTransHuge(page))
    + goto confused;
    zero_user_segment(page, first_hole << blkbits,
    PAGE_SIZE);
    if (first_hole == 0) {
    @@ -248,7 +272,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
    goto set_error_page;
    }
    bio = bio_alloc(GFP_KERNEL,
    - min_t(int, nr_pages, BIO_MAX_PAGES));
    + min_t(int, nr, BIO_MAX_PAGES));
    if (!bio) {
    if (ctx)
    fscrypt_release_ctx(ctx);
    @@ -289,5 +313,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
    BUG_ON(pages && !list_empty(pages));
    if (bio)
    submit_bio(bio);
    + if (blocks != blocks_on_stack)
    + kfree(blocks);
    return 0;
    }
    --
    2.8.1
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