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    Subject[PATCH 3.11 146/208] mm: numa: do not clear PMD during PTE update scan
    Date
    3.11.10.3 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mel Gorman <mgorman@suse.de>

    commit 5a6dac3ec5f583cc8ee7bc53b5500a207c4ca433 upstream.

    If the PMD is flushed then a parallel fault in handle_mm_fault() will
    enter the pmd_none and do_huge_pmd_anonymous_page() path where it'll
    attempt to insert a huge zero page. This is wasteful so the patch
    avoids clearing the PMD when setting pmd_numa.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    Cc: Alex Thorlton <athorlton@sgi.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    mm/huge_memory.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index 72da10d..ac2546c 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1486,20 +1486,22 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,

    if (__pmd_trans_huge_lock(pmd, vma) == 1) {
    pmd_t entry;
    - entry = pmdp_get_and_clear(mm, addr, pmd);
    if (!prot_numa) {
    + entry = pmdp_get_and_clear(mm, addr, pmd);
    entry = pmd_modify(entry, newprot);
    BUG_ON(pmd_write(entry));
    + set_pmd_at(mm, addr, pmd, entry);
    } else {
    struct page *page = pmd_page(*pmd);
    + entry = *pmd;

    /* only check non-shared pages */
    if (page_mapcount(page) == 1 &&
    !pmd_numa(*pmd)) {
    entry = pmd_mknuma(entry);
    + set_pmd_at(mm, addr, pmd, entry);
    }
    }
    - set_pmd_at(mm, addr, pmd, entry);
    spin_unlock(&vma->vm_mm->page_table_lock);
    ret = 1;
    }
    --
    1.8.3.2


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