From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [patch 029/101] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Date: Thu, 28 Jul 2016 15:45:59 -0700 Message-ID: <579a8b27.8x78MLx5j1gGjeE1%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:56811 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752106AbcG1WqA (ORCPT ); Thu, 28 Jul 2016 18:46:00 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: torvalds@linux-foundation.org, mm-commits@vger.kernel.org, akpm@linux-foundation.org, mgorman@techsingularity.net, hannes@cmpxchg.org, hillf.zj@alibaba-inc.com, iamjoonsoo.kim@lge.com, mhocko@kernel.org, minchan@kernel.org, riel@surriel.com, vbabka@suse.cz From: Mel Gorman Subject: mm: vmscan: do not reclaim from kswapd if there is any eligible zone kswapd scans from highest to lowest for a zone that requires balancing. This was necessary when reclaim was per-zone to fairly age pages on lower zones. Now that we are reclaiming on a per-node basis, any eligible zone can be used and pages will still be aged fairly. This patch avoids reclaiming excessively unless buffer_heads are over the limit and it's necessary to reclaim from a higher zone than requested by the waker of kswapd to relieve low memory pressure. [hillf.zj@alibaba-inc.com: Force kswapd reclaim no more than needed] Link: http://lkml.kernel.org/r/1466518566-30034-12-git-send-email-mgorman@techsingularity.net Link: http://lkml.kernel.org/r/1467970510-21195-13-git-send-email-mgorman@techsingularity.net Signed-off-by: Mel Gorman Signed-off-by: Hillf Danton Acked-by: Vlastimil Babka Acked-by: Johannes Weiner Cc: Joonsoo Kim Cc: Michal Hocko Cc: Minchan Kim Cc: Rik van Riel Signed-off-by: Andrew Morton --- mm/vmscan.c | 59 ++++++++++++++++++++++---------------------------- 1 file changed, 27 insertions(+), 32 deletions(-) diff -puN mm/vmscan.c~mm-vmscan-do-not-reclaim-from-kswapd-if-there-is-any-eligible-zone mm/vmscan.c --- a/mm/vmscan.c~mm-vmscan-do-not-reclaim-from-kswapd-if-there-is-any-eligible-zone +++ a/mm/vmscan.c @@ -3144,31 +3144,39 @@ static int balance_pgdat(pg_data_t *pgda sc.nr_reclaimed = 0; - /* Scan from the highest requested zone to dma */ - for (i = classzone_idx; i >= 0; i--) { - zone = pgdat->node_zones + i; - if (!populated_zone(zone)) - continue; - - /* - * If the number of buffer_heads in the machine - * exceeds the maximum allowed level and this node - * has a highmem zone, force kswapd to reclaim from - * it to relieve lowmem pressure. - */ - if (buffer_heads_over_limit && is_highmem_idx(i)) { - classzone_idx = i; - break; - } + /* + * If the number of buffer_heads in the machine exceeds the + * maximum allowed level then reclaim from all zones. This is + * not specific to highmem as highmem may not exist but it is + * it is expected that buffer_heads are stripped in writeback. + */ + if (buffer_heads_over_limit) { + for (i = MAX_NR_ZONES - 1; i >= 0; i--) { + zone = pgdat->node_zones + i; + if (!populated_zone(zone)) + continue; - if (!zone_balanced(zone, order, 0)) { classzone_idx = i; break; } } - if (i < 0) - goto out; + /* + * Only reclaim if there are no eligible zones. Check from + * high to low zone as allocations prefer higher zones. + * Scanning from low to high zone would allow congestion to be + * cleared during a very small window when a small low + * zone was balanced even under extreme pressure when the + * overall node may be congested. + */ + for (i = classzone_idx; i >= 0; i--) { + zone = pgdat->node_zones + i; + if (!populated_zone(zone)) + continue; + + if (zone_balanced(zone, sc.order, classzone_idx)) + goto out; + } /* * Do some background aging of the anon list, to give @@ -3214,19 +3222,6 @@ static int balance_pgdat(pg_data_t *pgda break; /* - * Stop reclaiming if any eligible zone is balanced and clear - * node writeback or congested. - */ - for (i = 0; i <= classzone_idx; i++) { - zone = pgdat->node_zones + i; - if (!populated_zone(zone)) - continue; - - if (zone_balanced(zone, sc.order, classzone_idx)) - goto out; - }