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    Subject[PATCH 3.18 08/21] mm: fix the NULL mapping case in __isolate_lru_page()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Hugh Dickins <hughd@google.com>

    commit 145e1a71e090575c74969e3daa8136d1e5b99fc8 upstream.

    George Boole would have noticed a slight error in 4.16 commit
    69d763fc6d3a ("mm: pin address_space before dereferencing it while
    isolating an LRU page"). Fix it, to match both the comment above it,
    and the original behaviour.

    Although anonymous pages are not marked PageDirty at first, we have an
    old habit of calling SetPageDirty when a page is removed from swap
    cache: so there's a category of ex-swap pages that are easily
    migratable, but were inadvertently excluded from compaction's async
    migration in 4.16.

    Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1805302014001.12558@eggly.anvils
    Fixes: 69d763fc6d3a ("mm: pin address_space before dereferencing it while isolating an LRU page")
    Signed-off-by: Hugh Dickins <hughd@google.com>
    Acked-by: Minchan Kim <minchan@kernel.org>
    Acked-by: Mel Gorman <mgorman@techsingularity.net>
    Reported-by: Ivan Kalvachev <ikalvachev@gmail.com>
    Cc: "Huang, Ying" <ying.huang@intel.com>
    Cc: Jan Kara <jack@suse.cz>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/vmscan.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1234,7 +1234,7 @@ int __isolate_lru_page(struct page *page
    return ret;

    mapping = page_mapping(page);
    - migrate_dirty = mapping && mapping->a_ops->migratepage;
    + migrate_dirty = !mapping || mapping->a_ops->migratepage;
    unlock_page(page);
    if (!migrate_dirty)
    return ret;

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