Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754288Ab0LILSY (ORCPT ); Thu, 9 Dec 2010 06:18:24 -0500 Received: from gir.skynet.ie ([193.1.99.77]:47651 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751105Ab0LILSW (ORCPT ); Thu, 9 Dec 2010 06:18:22 -0500 From: Mel Gorman To: Simon Kirby Cc: KOSAKI Motohiro , Shaohua Li , Dave Hansen , Johannes Weiner , Andrew Morton , linux-mm , linux-kernel , Mel Gorman Subject: [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node is balanced Date: Thu, 9 Dec 2010 11:18:16 +0000 Message-Id: <1291893500-12342-3-git-send-email-mel@csn.ul.ie> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1291893500-12342-1-git-send-email-mel@csn.ul.ie> References: <1291893500-12342-1-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: 4147 Lines: 124 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 | 43 ++++++++++++++++++++++++++++++++++--------- 1 files changed, 34 insertions(+), 9 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 25cb373..b4472a1 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2117,10 +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 int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) { int i; + unsigned long balanced = 0; + bool all_zones_ok = true; /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ if (remaining) @@ -2138,10 +2154,19 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) if (!zone_watermark_ok(zone, order, high_wmark_pages(zone), 0, 0)) - return 1; + all_zones_ok = false; + else + balanced += zone->present_pages; } - return 0; + /* + * For high-order requests, any zone meeting the watermark allows + * kswapd to sleep. For order-0, all zones must be balanced + */ + if (order) + return pgdat_balanced(pgdat, balanced); + else + return !all_zones_ok; } /* @@ -2169,7 +2194,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) { int all_zones_ok; - int any_zone_ok; + unsigned long balanced; int priority; int i; int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ @@ -2203,7 +2228,7 @@ loop_again: disable_swap_token(); all_zones_ok = 1; - any_zone_ok = 0; + balanced = 0; /* * Scan in the highmem->dma direction for the highest @@ -2314,11 +2339,11 @@ loop_again: */ zone_clear_flag(zone, ZONE_CONGESTED); if (i <= classzone_idx) - 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 @@ -2344,10 +2369,10 @@ out: /* * order-0: All zones must meet high watermark for a balanced node - * high-order: Any zone below pgdats classzone_idx must meet the high - * watermark for a balanced node + * high-order: Balanced zones must make up at least 25% of the node + * for the node to be balanced */ - 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/