Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755218Ab0K3RPr (ORCPT ); Tue, 30 Nov 2010 12:15:47 -0500 Received: from gir.skynet.ie ([193.1.99.77]:46857 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755022Ab0K3RPk (ORCPT ); Tue, 30 Nov 2010 12:15:40 -0500 From: Mel Gorman To: Simon Kirby Cc: KOSAKI Motohiro , Shaohua Li , Dave Hansen , linux-mm , linux-kernel , Mel Gorman Subject: [PATCH 3/3] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node is balanced Date: Tue, 30 Nov 2010 17:15:39 +0000 Message-Id: <1291137339-6323-4-git-send-email-mel@csn.ul.ie> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1291137339-6323-1-git-send-email-mel@csn.ul.ie> References: <1291137339-6323-1-git-send-email-mel@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3837 Lines: 116 When reclaiming for high-orders, kswapd is responsible for balancing a node but it should not reclaim excessively. It avoids excessive reclaim by considering if any zone in a node is balanced then the node is balanced. In the cases where there are imbalanced zone sizes (e.g. ZONE_DMA with both ZONE_DMA32 and ZONE_NORMAL), kswapd can go to sleep prematurely as just one small zone was balanced. This alters the sleep logic of kswapd slightly. It counts the number of pages that make up the balanced zones. If the total number of balanced pages is more than a quarter of the zone, kswapd will go back to sleep. This should keep a node balanced without reclaiming an excessive number of pages. Signed-off-by: Mel Gorman --- mm/vmscan.c | 30 ++++++++++++++++++++++-------- 1 files changed, 22 insertions(+), 8 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 9891efd..77c511f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2117,12 +2117,26 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, } #endif +/* + * pgdat_balanced is used when checking if a node is balanced for high-order + * allocations. Only zones that meet watermarks make up "balanced". + * The total of balanced pages must be at least 25% of the node for the + * node to be considered balanced. Forcing all zones to be balanced for high + * orders can cause excessive reclaim when there are imbalanced zones. + * Similarly, we do not want kswapd to go to sleep because ZONE_DMA happens + * to be balanced when ZONE_DMA32 is huge in comparison and unbalanced + */ +static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced) +{ + return balanced > pgdat->node_present_pages / 4; +} + /* is kswapd sleeping prematurely? */ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) { int i; + unsigned long balanced = 0; bool all_zones_ok = true; - bool any_zone_ok = false; /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ if (remaining) @@ -2142,7 +2156,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) 0, 0)) all_zones_ok = false; else - any_zone_ok = true; + balanced += zone->present_pages; } /* @@ -2151,7 +2165,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) * For order-0, all zones must be balanced */ if (order) - return !any_zone_ok; + return pgdat_balanced(pgdat, balanced); else return !all_zones_ok; } @@ -2181,7 +2195,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, int high_zoneidx) { int all_zones_ok; - int any_zone_ok; + unsigned long balanced; int priority; int i; int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ @@ -2215,7 +2229,7 @@ loop_again: disable_swap_token(); all_zones_ok = 1; - any_zone_ok = 0; + balanced = 0; /* * Scan in the highmem->dma direction for the highest @@ -2326,11 +2340,11 @@ loop_again: */ zone_clear_flag(zone, ZONE_CONGESTED); if (i <= high_zoneidx) - any_zone_ok = 1; + balanced += zone->present_pages; } } - if (all_zones_ok || (order && any_zone_ok)) + if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced))) break; /* kswapd: all done */ /* * OK, kswapd is getting into trouble. Take a nap, then take @@ -2353,7 +2367,7 @@ loop_again: break; } out: - if (!(all_zones_ok || (order && any_zone_ok))) { + if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced)))) { cond_resched(); try_to_freeze(); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/