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    Subject[PATCH] mm: migrate: One less atomic operation
    From
    Date
    From 3754c8617ef4377ce2ca2e3b28bdc28f8de1aa0d Mon Sep 17 00:00:00 2001
    From: Jacobo Giralt <jacobo.giralt@gmail.com>
    Date: Sat, 5 Nov 2011 13:12:50 +0100
    Subject: [PATCH] mm: migrate: One less atomic operation

    migrate_page_move_mapping drops a reference from the
    old page after unfreezing its counter. Both operations
    can be merged into a single atomic operation by
    directly unfreezing to one less reference.

    The same applies to migrate_huge_page_move_mapping.

    Signed-off-by: Jacobo Giralt <jacobo.giralt@gmail.com>
    ---
    mm/migrate.c | 10 ++++------
    1 files changed, 4 insertions(+), 6 deletions(-)

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 33358f8..46d04a0 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -269,12 +269,12 @@ static int migrate_page_move_mapping(struct address_space *mapping,

    radix_tree_replace_slot(pslot, newpage);

    - page_unfreeze_refs(page, expected_count);
    /*
    - * Drop cache reference from old page.
    + * Drop cache reference from old page by unfreezing
    + * to one less reference.
    * We know this isn't the last reference.
    */
    - __put_page(page);
    + page_unfreeze_refs(page, expected_count - 1);

    /*
    * If moved to a different zone then also account
    @@ -334,9 +334,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,

    radix_tree_replace_slot(pslot, newpage);

    - page_unfreeze_refs(page, expected_count);
    -
    - __put_page(page);
    + page_unfreeze_refs(page, expected_count - 1);

    spin_unlock_irq(&mapping->tree_lock);
    return 0;
    --
    1.7.5.4




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