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    Subject[Patch v4 4/4] mm/mremap: use pmd_addr_end to simplify the calculate of extent
    Date
    The purpose of this code is to calculate the smaller extent in old and
    new range. Let's leverage pmd_addr_end() to do the calculation.

    Hope this would make the code easier to read.

    Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>

    ---
    v4: remove redundant parentheses pointed by Kirill
    ---
    mm/mremap.c | 16 +++++++---------
    1 file changed, 7 insertions(+), 9 deletions(-)

    diff --git a/mm/mremap.c b/mm/mremap.c
    index f5f17d050617..f6f56aa0b893 100644
    --- a/mm/mremap.c
    +++ b/mm/mremap.c
    @@ -237,11 +237,12 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
    unsigned long new_addr, unsigned long len,
    bool need_rmap_locks)
    {
    - unsigned long extent, next, old_end;
    + unsigned long extent, old_next, new_next, old_end, new_end;
    struct mmu_notifier_range range;
    pmd_t *old_pmd, *new_pmd;

    old_end = old_addr + len;
    + new_end = new_addr + len;
    flush_cache_range(vma, old_addr, old_end);

    mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
    @@ -250,14 +251,11 @@ unsigned long move_page_tables(struct vm_area_struct *vma,

    for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
    cond_resched();
    - next = (old_addr + PMD_SIZE) & PMD_MASK;
    - /* even if next overflowed, extent below will be ok */
    - extent = next - old_addr;
    - if (extent > old_end - old_addr)
    - extent = old_end - old_addr;
    - next = (new_addr + PMD_SIZE) & PMD_MASK;
    - if (extent > next - new_addr)
    - extent = next - new_addr;
    +
    + old_next = pmd_addr_end(old_addr, old_end);
    + new_next = pmd_addr_end(new_addr, new_end);
    + extent = min(old_next - old_addr, new_next - new_addr);
    +
    old_pmd = get_old_pmd(vma->vm_mm, old_addr);
    if (!old_pmd)
    continue;
    --
    2.20.1 (Apple Git-117)
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