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    Subject[PATCH 2/7] vmscan: synchronous lumpy reclaim don't call congestion_wait()
    Date
    congestion_wait() mean "waiting quueue congestion is cleared".
    That said, if the system have plenty dirty pages and flusher thread push
    new request to IO queue conteniously, IO queue are not cleared
    congestion status for long time. thus, congestion_wait(HZ/10) become
    almostly equivalent schedule_timeout(HZ/10).

    However, synchronous lumpy reclaim donesn't need this
    congestion_wait() at all. shrink_page_list(PAGEOUT_IO_SYNC) are
    using wait_on_page_writeback() and it provide sufficient waiting.

    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    ---
    mm/vmscan.c | 1 -
    1 files changed, 0 insertions(+), 1 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index cf51d62..1cdc3db 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1341,7 +1341,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,

    /* Check if we should syncronously wait for writeback */
    if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
    - congestion_wait(BLK_RW_ASYNC, HZ/10);
    /*
    * The attempt at page out may have made some
    * of the pages active, mark them inactive again.
    --
    1.6.5.2




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