Re: [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone

Vlastimil Babka
2016-06-17T10:46:10Z

On 06/09/2016 08:04 PM, Mel Gorman wrote:
> kswapd is woken when zones are below the low watermark but the wakeup
> decision is not taking the classzone into account. Now that reclaim is
> node-based, it is only required to wake kswapd once per node and only if
> all zones are unbalanced for the requested classzone.
>
> Note that one node might be checked multiple times but there is no cheap
> way of tracking what nodes have already been visited for zoneslists that
> be ordered by either zone or node.

Wouldn't it be possible to optimize for node order as you did in direct reclaim?
Do the zone_balanced checks when going through zonelist, and once node changes
in iteration, wake up if no eligible zones visited so far were balanced.

> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
> mm/vmscan.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7a2d69612231..b9cff9047ac0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3389,6 +3389,7 @@ static int kswapd(void *p)
> void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
> {
> pg_data_t *pgdat;
> + int z;
>
> if (!populated_zone(zone))
> return;
> @@ -3402,8 +3403,16 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
> pgdat->kswapd_order = max(pgdat->kswapd_order, order);
> if (!waitqueue_active(&pgdat->kswapd_wait))
> return;
> - if (zone_balanced(zone, order, 0))
> - return;
> +
> + /* Only wake kswapd if all zones are unbalanced */
> + for (z = 0; z <= classzone_idx; z++) {
> + zone = pgdat->node_zones + z;
> + if (!populated_zone(zone))
> + continue;
> +
> + if (zone_balanced(zone, order, classzone_idx))
> + return;
> + }
>
> trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
> wake_up_interruptible(&pgdat->kswapd_wait);
>