Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753955Ab0LJKT4 (ORCPT ); Fri, 10 Dec 2010 05:19:56 -0500 Received: from gir.skynet.ie ([193.1.99.77]:58027 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751428Ab0LJKTy (ORCPT ); Fri, 10 Dec 2010 05:19:54 -0500 Date: Fri, 10 Dec 2010 10:19:36 +0000 From: Mel Gorman To: Minchan Kim Cc: Simon Kirby , KOSAKI Motohiro , Shaohua Li , Dave Hansen , Johannes Weiner , Andrew Morton , linux-mm , linux-kernel Subject: Re: [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node is balanced Message-ID: <20101210101935.GI20133@csn.ul.ie> References: <1291893500-12342-1-git-send-email-mel@csn.ul.ie> <1291893500-12342-3-git-send-email-mel@csn.ul.ie> <20101209154258.GC1740@barrios-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20101209154258.GC1740@barrios-desktop> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6619 Lines: 187 On Fri, Dec 10, 2010 at 12:42:58AM +0900, Minchan Kim wrote: > On Thu, Dec 09, 2010 at 11:18:16AM +0000, Mel Gorman wrote: > > 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 > Reviewed-by: Minchan Kim > > Just below trivials. > > > --- > > 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 > > Could you write down why you select 25% in description? > It could help someone who try to change that watermark in future. > Sure, how about; +/* + * 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. + * The choice of 25% is due to + * o a 16M DMA zone that is balanced will not balance a zone on any + * reasonable sized machine + * o On all other machines, the top zone must be at least a reasonable + * precentage of the middle zones. For example, on 32-bit x86, highmem + * would need to be at least 256M for it to be balance a whole node. + * Similarly, on x86-64 the Normal zone would need to be at least 1G + * to balance a node on its own. These seemed like reasonable ratios. + */ +static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced) +{ + return balanced > pgdat->node_present_pages / 4; +} ? > > + * 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) > > I think balanced_pages is more clear. > But it's a preference. > Updated. > > +{ > > + 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 > > The comment isn't exact. > could allow? > Correct; + /* + * For high-order requests, the balanced zones must contain at least + * 25% of the nodes pages for kswapd to sleep. For order-0, all zones + * must be balanced + */ + if (order) + return pgdat_balanced(pgdat, balanced); + else + return !all_zones_ok; Thanks > > + */ > > + 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(); -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/