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    Subject[PATCH v2 01/10] Make clear description of isolate/putback functions
    Date
    Commonly, putback_lru_page is used with isolated_lru_page.
    The isolated_lru_page picks the page in middle of LRU and
    putback_lru_page insert the lru in head of LRU.
    It means it could make LRU churning so we have to be very careful.
    Let's clear description of isolate/putback functions.

    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Acked-by: Johannes Weiner <hannes@cmpxchg.org>
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
    ---
    mm/migrate.c | 2 +-
    mm/vmscan.c | 8 ++++++--
    2 files changed, 7 insertions(+), 3 deletions(-)

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 34132f8..819d233 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -68,7 +68,7 @@ int migrate_prep_local(void)
    }

    /*
    - * Add isolated pages on the list back to the LRU under page lock
    + * Add isolated pages on the list back to the LRU's head under page lock
    * to avoid leaking evictable pages back onto unevictable list.
    */
    void putback_lru_pages(struct list_head *l)
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 8bfd450..a658dde 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -551,10 +551,10 @@ int remove_mapping(struct address_space *mapping, struct page *page)
    }

    /**
    - * putback_lru_page - put previously isolated page onto appropriate LRU list
    + * putback_lru_page - put previously isolated page onto appropriate LRU list's head
    * @page: page to be put back to appropriate lru list
    *
    - * Add previously isolated @page to appropriate LRU list.
    + * Add previously isolated @page to appropriate LRU list's head
    * Page may still be unevictable for other reasons.
    *
    * lru_lock must not be held, interrupts must be enabled.
    @@ -1196,6 +1196,10 @@ static unsigned long clear_active_flags(struct list_head *page_list,
    * without a stable reference).
    * (2) the lru_lock must not be held.
    * (3) interrupts must be enabled.
    + *
    + * NOTE : This function removes the page from LRU list and putback_lru_page
    + * insert the page to LRU list's head. It means it makes LRU churing so you
    + * have to use the function carefully.
    */
    int isolate_lru_page(struct page *page)
    {
    --
    1.7.0.4


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