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    Subject[PATCH 6/7] shmem: rework majmin and ZERO_PAGE
    Very minor adjustments to shmem_getpage return path: I now prefer it to
    return NULL and let do_shmem_file_read use ZERO_PAGE(0) in that case;
    and we don't need a local majmin variable, do_no_page initializes *type
    to VM_FAULT_MINOR already.

    Signed-off-by: Hugh Dickins <hugh@veritas.com>
    ---

    mm/shmem.c | 26 ++++++++++++--------------
    1 files changed, 12 insertions(+), 14 deletions(-)

    --- shmem5/mm/shmem.c 2004-09-05 17:06:30.195820472 +0100
    +++ shmem6/mm/shmem.c 2004-09-05 17:06:41.258138744 +0100
    @@ -885,7 +885,7 @@ static int shmem_getpage(struct inode *i
    struct page *swappage;
    swp_entry_t *entry;
    swp_entry_t swap;
    - int error, majmin = VM_FAULT_MINOR;
    + int error;

    if (idx >= SHMEM_MAX_INDEX)
    return -EFBIG;
    @@ -923,9 +923,10 @@ repeat:
    shmem_swp_unmap(entry);
    spin_unlock(&info->lock);
    /* here we actually do the io */
    - if (majmin == VM_FAULT_MINOR && type)
    + if (type && *type == VM_FAULT_MINOR) {
    inc_page_state(pgmajfault);
    - majmin = VM_FAULT_MAJOR;
    + *type = VM_FAULT_MAJOR;
    + }
    swappage = shmem_swapin(info, swap, idx);
    if (!swappage) {
    spin_lock(&info->lock);
    @@ -1077,15 +1078,10 @@ repeat:
    SetPageUptodate(filepage);
    }
    done:
    - if (!*pagep) {
    - if (filepage) {
    - unlock_page(filepage);
    - *pagep = filepage;
    - } else
    - *pagep = ZERO_PAGE(0);
    + if (*pagep != filepage) {
    + unlock_page(filepage);
    + *pagep = filepage;
    }
    - if (type)
    - *type = majmin;
    return 0;

    failed:
    @@ -1442,13 +1438,14 @@ static void do_shmem_file_read(struct fi
    if (index == end_index) {
    nr = i_size & ~PAGE_CACHE_MASK;
    if (nr <= offset) {
    - page_cache_release(page);
    + if (page)
    + page_cache_release(page);
    break;
    }
    }
    nr -= offset;

    - if (page != ZERO_PAGE(0)) {
    + if (page) {
    /*
    * If users can be writing to this page using arbitrary
    * virtual addresses, take care about potential aliasing
    @@ -1461,7 +1458,8 @@ static void do_shmem_file_read(struct fi
    */
    if (!offset)
    mark_page_accessed(page);
    - }
    + } else
    + page = ZERO_PAGE(0);

    /*
    * Ok, we have the page, and it's up-to-date, so
    -
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