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    Subject[tip:sched/core] mm: Do not flush TLB during protection change if !pte_present && !migration_entry
    Commit-ID:  e920e14ca29b0b2a981cfc90e4e20edd6f078d19
    Gitweb: http://git.kernel.org/tip/e920e14ca29b0b2a981cfc90e4e20edd6f078d19
    Author: Mel Gorman <mgorman@suse.de>
    AuthorDate: Mon, 7 Oct 2013 11:28:48 +0100
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 9 Oct 2013 12:39:48 +0200

    mm: Do not flush TLB during protection change if !pte_present && !migration_entry

    NUMA PTE scanning is expensive both in terms of the scanning itself and
    the TLB flush if there are any updates. Currently non-present PTEs are
    accounted for as an update and incurring a TLB flush where it is only
    necessary for anonymous migration entries. This patch addresses the
    problem and should reduce TLB flushes.

    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1381141781-10992-11-git-send-email-mgorman@suse.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    mm/mprotect.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/mm/mprotect.c b/mm/mprotect.c
    index 2bbb648..7bdbd4b 100644
    --- a/mm/mprotect.c
    +++ b/mm/mprotect.c
    @@ -101,8 +101,9 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
    make_migration_entry_read(&entry);
    set_pte_at(mm, addr, pte,
    swp_entry_to_pte(entry));
    +
    + pages++;
    }
    - pages++;
    }
    } while (pte++, addr += PAGE_SIZE, addr != end);
    arch_leave_lazy_mmu_mode();

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