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SubjectRe: [PATCH 11/34] mm, vmscan: remove duplicate logic clearing node congestion and dirty state
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On 07/08/2016 11:34 AM, Mel Gorman wrote:
> Reclaim may stall if there is too much dirty or congested data on a node.
> This was previously based on zone flags and the logic for clearing the
> flags is in two places. As congestion/dirty tracking is now tracked on a
> per-node basis, we can remove some duplicate logic.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>

I don't think it's that big a side-effect to be concerned. I would be
more worried about frequently dirtying cache lines from other
zone_balanced callers where, but I guess even the calls from
wakeup_kswapd() rarely return true for zone_balanced(), otherwise the
wakeups wouldn't have a reason to happen.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/vmscan.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 01fe4708e404..8b39b903bd14 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3008,7 +3008,17 @@ static bool zone_balanced(struct zone *zone, int order, int classzone_idx)
> {
> unsigned long mark = high_wmark_pages(zone);
>
> - return zone_watermark_ok_safe(zone, order, mark, classzone_idx);
> + if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
> + return false;
> +
> + /*
> + * If any eligible zone is balanced then the node is not considered
> + * to be congested or dirty
> + */
> + clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
> + clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
> +
> + return true;
> }
>
> /*
> @@ -3154,13 +3164,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
> if (!zone_balanced(zone, order, 0)) {
> classzone_idx = i;
> break;
> - } else {
> - /*
> - * If any eligible zone is balanced then the
> - * node is not considered congested or dirty.
> - */
> - clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
> - clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
> }
> }
>
> @@ -3219,11 +3222,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
> if (!populated_zone(zone))
> continue;
>
> - if (zone_balanced(zone, sc.order, classzone_idx)) {
> - clear_bit(PGDAT_CONGESTED, &pgdat->flags);
> - clear_bit(PGDAT_DIRTY, &pgdat->flags);
> + if (zone_balanced(zone, sc.order, classzone_idx))
> goto out;
> - }
> }
>
> /*
>

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