From 39d18dc4b8b0c000fa681cbae10ac3f8a132814b Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 29 Nov 2012 13:54:23 -0800 Subject: mm: vmscan: fix endless loop in kswapd balancing commit 60cefed485a02bd99b6299dad70666fe49245da7 upstream. Kswapd does not in all places have the same criteria for a balanced zone. Zones are only being reclaimed when their high watermark is breached, but compaction checks loop over the zonelist again when the zone does not meet the low watermark plus two times the size of the allocation. This gets kswapd stuck in an endless loop over a small zone, like the DMA zone, where the high watermark is smaller than the compaction requirement. Add a function, zone_balanced(), that checks the watermark, and, for higher order allocations, if compaction has enough free memory. Then use it uniformly to check for balanced zones. This makes sure that when the compaction watermark is not met, at least reclaim happens and progress is made - or the zone is declared unreclaimable at some point and skipped entirely. Signed-off-by: Johannes Weiner Reported-by: George Spelvin Reported-by: Johannes Hirte Reported-by: Tomas Racek Tested-by: Johannes Hirte Reviewed-by: Rik van Riel Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- mm/vmscan.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 313381cc88a..1e4ee1acd2b 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2492,6 +2492,19 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, } #endif +static bool zone_balanced(struct zone *zone, int order, + unsigned long balance_gap, int classzone_idx) +{ + if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + + balance_gap, classzone_idx, 0)) + return false; + + if (COMPACTION_BUILD && order && !compaction_suitable(zone, order)) + return false; + + return true; +} + /* * pgdat_balanced is used when checking if a node is balanced for high-order * allocations. Only zones that meet watermarks and are in a zone allowed @@ -2551,8 +2564,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, continue; } - if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), - i, 0)) + if (!zone_balanced(zone, order, 0, i)) all_zones_ok = false; else balanced += zone->present_pages; @@ -2655,8 +2667,7 @@ loop_again: shrink_active_list(SWAP_CLUSTER_MAX, zone, &sc, priority, 0); - if (!zone_watermark_ok_safe(zone, order, - high_wmark_pages(zone), 0, 0)) { + if (!zone_balanced(zone, order, 0, 0)) { end_zone = i; break; } else { @@ -2717,9 +2728,8 @@ loop_again: (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / KSWAPD_ZONE_BALANCE_GAP_RATIO); - if (!zone_watermark_ok_safe(zone, order, - high_wmark_pages(zone) + balance_gap, - end_zone, 0)) { + if (!zone_balanced(zone, order, + balance_gap, end_zone)) { shrink_zone(priority, zone, &sc); reclaim_state->reclaimed_slab = 0; @@ -2746,8 +2756,7 @@ loop_again: continue; } - if (!zone_watermark_ok_safe(zone, order, - high_wmark_pages(zone), end_zone, 0)) { + if (!zone_balanced(zone, order, 0, end_zone)) { all_zones_ok = 0; /* * We are still under min water mark. This -- cgit v1.2.3-18-g5258