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 <[email protected]> --- 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); /* * 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
