lkml.org 
[lkml]   [2012]   [Jul]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[ 26/41] kswapd: avoid unnecessary rebalance after an unsuccessful balancing
    Date
    From: Greg KH <gregkh@linuxfoundation.org>

    3.0-stable review patch. If anyone has any objections, please let me know.

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

    From: Alex Shi <alex.shi@intel.com>

    commit d2ebd0f6b89567eb93ead4e2ca0cbe03021f344b upstream.

    Stable note: Fixes https://bugzilla.redhat.com/show_bug.cgi?id=712019. This
    patch reduces kswapd CPU usage.

    In commit 215ddd66 ("mm: vmscan: only read new_classzone_idx from pgdat
    when reclaiming successfully") , Mel Gorman said kswapd is better to sleep
    after a unsuccessful balancing if there is tighter reclaim request pending
    in the balancing. But in the following scenario, kswapd do something that
    is not matched our expectation. The patch fixes this issue.

    1, Read pgdat request A (classzone_idx, order = 3)
    2, balance_pgdat()
    3, During pgdat, a new pgdat request B (classzone_idx, order = 5) is placed
    4, balance_pgdat() returns but failed since returned order = 0
    5, pgdat of request A assigned to balance_pgdat(), and do balancing again.
    While the expectation behavior of kswapd should try to sleep.

    Signed-off-by: Alex Shi <alex.shi@intel.com>
    Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
    Acked-by: Mel Gorman <mgorman@suse.de>
    Tested-by: Pádraig Brady <P@draigBrady.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/vmscan.c | 14 +++++++++++---
    1 file changed, 11 insertions(+), 3 deletions(-)

    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2844,7 +2844,9 @@ static void kswapd_try_to_sleep(pg_data_
    static int kswapd(void *p)
    {
    unsigned long order, new_order;
    + unsigned balanced_order;
    int classzone_idx, new_classzone_idx;
    + int balanced_classzone_idx;
    pg_data_t *pgdat = (pg_data_t*)p;
    struct task_struct *tsk = current;

    @@ -2875,7 +2877,9 @@ static int kswapd(void *p)
    set_freezable();

    order = new_order = 0;
    + balanced_order = 0;
    classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
    + balanced_classzone_idx = classzone_idx;
    for ( ; ; ) {
    int ret;

    @@ -2884,7 +2888,8 @@ static int kswapd(void *p)
    * new request of a similar or harder type will succeed soon
    * so consider going to sleep on the basis we reclaimed at
    */
    - if (classzone_idx >= new_classzone_idx && order == new_order) {
    + if (balanced_classzone_idx >= new_classzone_idx &&
    + balanced_order == new_order) {
    new_order = pgdat->kswapd_max_order;
    new_classzone_idx = pgdat->classzone_idx;
    pgdat->kswapd_max_order = 0;
    @@ -2899,7 +2904,8 @@ static int kswapd(void *p)
    order = new_order;
    classzone_idx = new_classzone_idx;
    } else {
    - kswapd_try_to_sleep(pgdat, order, classzone_idx);
    + kswapd_try_to_sleep(pgdat, balanced_order,
    + balanced_classzone_idx);
    order = pgdat->kswapd_max_order;
    classzone_idx = pgdat->classzone_idx;
    pgdat->kswapd_max_order = 0;
    @@ -2916,7 +2922,9 @@ static int kswapd(void *p)
    */
    if (!ret) {
    trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
    - order = balance_pgdat(pgdat, order, &classzone_idx);
    + balanced_classzone_idx = classzone_idx;
    + balanced_order = balance_pgdat(pgdat, order,
    + &balanced_classzone_idx);
    }
    }
    return 0;

    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2012-07-30 20:41    [W:0.029 / U:36.212 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site