From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f71.google.com (mail-lf0-f71.google.com [209.85.215.71]) by kanga.kvack.org (Postfix) with ESMTP id 6FA2C828E1 for ; Tue, 31 May 2016 09:15:24 -0400 (EDT) Received: by mail-lf0-f71.google.com with SMTP id 132so72581424lfz.3 for ; Tue, 31 May 2016 06:15:24 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id ca3si41155944wjd.21.2016.05.31.06.08.37 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 31 May 2016 06:08:37 -0700 (PDT) From: Vlastimil Babka Subject: [PATCH v2 14/18] mm, compaction: create compact_gap wrapper Date: Tue, 31 May 2016 15:08:14 +0200 Message-Id: <20160531130818.28724-15-vbabka@suse.cz> In-Reply-To: <20160531130818.28724-1-vbabka@suse.cz> References: <20160531130818.28724-1-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Joonsoo Kim , David Rientjes , Rik van Riel , Vlastimil Babka Compaction uses a watermark gap of (2UL << order) pages at various places and it's not immediately obvious why. Abstract it through a compact_gap() wrapper to create a single place with a thorough explanation. Signed-off-by: Vlastimil Babka --- include/linux/compaction.h | 16 ++++++++++++++++ mm/compaction.c | 7 +++---- mm/vmscan.c | 4 ++-- 3 files changed, 21 insertions(+), 6 deletions(-) diff --git a/include/linux/compaction.h b/include/linux/compaction.h index 4bef69a83f8f..654cb74418c4 100644 --- a/include/linux/compaction.h +++ b/include/linux/compaction.h @@ -58,6 +58,22 @@ enum compact_result { struct alloc_context; /* in mm/internal.h */ +/* + * Number of free order-0 pages that should be available above given watermark + * to make sure compaction has reasonable chance of not running out of free + * pages that it needs to isolate as migration target during its work. + */ +static inline unsigned long compact_gap(unsigned int order) +{ + /* + * Although all the isolations for migration are temporary, compaction + * may have up to 1 << order pages on its list and then try to split + * an (order - 1) free page. At that point, a gap of 1 << order might + * not be enough, so it's safer to require twice that amount. + */ + return 2UL << order; +} + #ifdef CONFIG_COMPACTION extern int sysctl_compact_memory; extern int sysctl_compaction_handler(struct ctl_table *table, int write, diff --git a/mm/compaction.c b/mm/compaction.c index 4b21a26694a2..bcab680ccb8a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1337,11 +1337,10 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, return COMPACT_PARTIAL; /* - * Watermarks for order-0 must be met for compaction. Note the 2UL. - * This is because during migration, copies of pages need to be - * allocated and for a short time, the footprint is higher + * Watermarks for order-0 must be met for compaction to be able to + * isolate free pages for migration targets. */ - watermark = low_wmark_pages(zone) + (2UL << order); + watermark = low_wmark_pages(zone) + compact_gap(order); if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, alloc_flags, wmark_target)) return COMPACT_SKIPPED; diff --git a/mm/vmscan.c b/mm/vmscan.c index c4a2f4512fca..00034ec9229b 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2345,7 +2345,7 @@ static inline bool should_continue_reclaim(struct zone *zone, * If we have not reclaimed enough pages for compaction and the * inactive lists are large enough, continue reclaiming */ - pages_for_compaction = (2UL << sc->order); + pages_for_compaction = compact_gap(sc->order); inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE); if (get_nr_swap_pages() > 0) inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON); @@ -2472,7 +2472,7 @@ static inline bool compaction_ready(struct zone *zone, int order, int classzone_ */ balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP( zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO)); - watermark = high_wmark_pages(zone) + balance_gap + (2UL << order); + watermark = high_wmark_pages(zone) + balance_gap + compact_gap(order); watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, classzone_idx); /* -- 2.8.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org