On Sun, Mar 17, 2013 at 01:04:10PM +0000, 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>
>---
> mm/vmscan.c | 52 +++++++++++++++++++++-------------------------------
> 1 file changed, 21 insertions(+), 31 deletions(-)
>
>diff --git a/mm/vmscan.c b/mm/vmscan.c
>index 279d0c2..7513bd1 100644
>--- a/mm/vmscan.c
>+++ b/mm/vmscan.c
>@@ -2694,8 +2694,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>
> do {
> unsigned long lru_pages = 0;
>+ unsigned long nr_to_reclaim = 0;
> unsigned long nr_reclaimed = sc.nr_reclaimed;
>+ unsigned long this_reclaimed;
> bool raise_priority = true;
>+ bool pgdat_needs_compaction = true;
>
> /*
> * Scan in the highmem->dma direction for the highest
>@@ -2743,7 +2746,17 @@ 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);
>+
>+ /* Check if the memory needs to be defragmented */
>+ if (order && pgdat_needs_compaction &&
>+ zone_watermark_ok(zone, order,
>+ low_wmark_pages(zone),
>+ *classzone_idx, 0))
>+ pgdat_needs_compaction = false;
> }
>
> /*
>@@ -2814,6 +2827,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> */
> if (kswapd_shrink_zone(zone, &sc, lru_pages))
> raise_priority = false;
>+
>+ nr_to_reclaim += sc.nr_to_reclaim;
> }
>
> /*
>@@ -2864,46 +2879,21 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> if (try_to_freeze() || kthread_should_stop())
> break;
>
>- /* If no reclaim progress then increase scanning priority */
>- if (sc.nr_reclaimed - nr_reclaimed == 0)
>- raise_priority = true;
>+ /* Compact if necessary and kswapd is reclaiming efficiently */
>+ this_reclaimed = sc.nr_reclaimed - nr_reclaimed;
>+ if (order && pgdat_needs_compaction &&
>+ this_reclaimed > nr_to_reclaim)
>+ compact_pgdat(pgdat, order);
>
Hi Mel,
If you should check compaction_suitable here to confirm it's not because
other reasons like large number of pages under writeback to avoid blind
compaction. :-)
Regards,
Wanpeng Li
> /*
> * Raise priority if scanning rate is too low or there was no
> * progress in reclaiming pages
> */
>- if (raise_priority || sc.nr_reclaimed - nr_reclaimed == 0)
>+ if (raise_priority || !this_reclaimed)
> sc.priority--;
> } 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
>
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