On Mon 13-05-13 09:12:35, Mel Gorman wrote:
> In the past, kswapd makes a decision on whether to compact memory after the
> pgdat was considered balanced. This more or less worked but it is late to
> make such a decision and does not fit well now that kswapd makes a decision
> whether to exit the zone scanning loop depending on reclaim progress.
>
> This patch will compact a pgdat if at least the requested number of pages
> were reclaimed from unbalanced zones for a given priority. If any zone is
> currently balanced, kswapd will not call compaction as it is expected the
> necessary pages are already available.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/vmscan.c | 59 ++++++++++++++++++++++++++++++-----------------------------
> 1 file changed, 30 insertions(+), 29 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1c10ee5..cd09803 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2661,7 +2661,8 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
> */
> static bool kswapd_shrink_zone(struct zone *zone,
> struct scan_control *sc,
> - unsigned long lru_pages)
> + unsigned long lru_pages,
> + unsigned long *nr_attempted)
> {
> unsigned long nr_slab;
> struct reclaim_state *reclaim_state = current->reclaim_state;
> @@ -2677,6 +2678,9 @@ static bool kswapd_shrink_zone(struct zone *zone,
> nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
> sc->nr_reclaimed += reclaim_state->reclaimed_slab;
>
> + /* Account for the number of pages attempted to reclaim */
> + *nr_attempted += sc->nr_to_reclaim;
> +
> if (nr_slab == 0 && !zone_reclaimable(zone))
> zone->all_unreclaimable = 1;
>
> @@ -2724,7 +2728,9 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>
> do {
> unsigned long lru_pages = 0;
> + unsigned long nr_attempted = 0;
> bool raise_priority = true;
> + bool pgdat_needs_compaction = (order > 0);
>
> sc.nr_reclaimed = 0;
>
> @@ -2774,7 +2780,21 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> for (i = 0; i <= end_zone; i++) {
> struct zone *zone = pgdat->node_zones + i;
>
> + if (!populated_zone(zone))
> + continue;
> +
> lru_pages += zone_reclaimable_pages(zone);
> +
> + /*
> + * If any zone is currently balanced then kswapd will
> + * not call compaction as it is expected that the
> + * necessary pages are already available.
> + */
> + if (pgdat_needs_compaction &&
> + zone_watermark_ok(zone, order,
> + low_wmark_pages(zone),
> + *classzone_idx, 0))
> + pgdat_needs_compaction = false;
> }
>
> /*
> @@ -2843,7 +2863,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> * already being scanned that high
> * watermark would be met at 100% efficiency.
> */
> - if (kswapd_shrink_zone(zone, &sc, lru_pages))
> + if (kswapd_shrink_zone(zone, &sc, lru_pages,
> + &nr_attempted))
> raise_priority = false;
> }
>
> @@ -2896,6 +2917,13 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> break;
>
> /*
> + * Compact if necessary and kswapd is reclaiming at least the
> + * high watermark number of pages as requsted
> + */
> + if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
> + compact_pgdat(pgdat, order);
> +
> + /*
> * Raise priority if scanning rate is too low or there was no
> * progress in reclaiming pages
> */
> @@ -2904,33 +2932,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> } while (sc.priority >= 0 &&
> !pgdat_balanced(pgdat, order, *classzone_idx));
>
> - /*
> - * If kswapd was reclaiming at a higher order, it has the option of
> - * sleeping without all zones being balanced. Before it does, it must
> - * ensure that the watermarks for order-0 on *all* zones are met and
> - * that the congestion flags are cleared. The congestion flag must
> - * be cleared as kswapd is the only mechanism that clears the flag
> - * and it is potentially going to sleep here.
> - */
> - if (order) {
> - int zones_need_compaction = 1;
> -
> - for (i = 0; i <= end_zone; i++) {
> - struct zone *zone = pgdat->node_zones + i;
> -
> - if (!populated_zone(zone))
> - continue;
> -
> - /* Check if the memory needs to be defragmented. */
> - if (zone_watermark_ok(zone, order,
> - low_wmark_pages(zone), *classzone_idx, 0))
> - zones_need_compaction = 0;
> - }
> -
> - if (zones_need_compaction)
> - compact_pgdat(pgdat, order);
> - }
> -
> out:
> /*
> * Return the order we were reclaiming at so prepare_kswapd_sleep()
> --
> 1.8.1.4
>
--
Michal Hocko
SUSE Labs
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