From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754074AbcFPKJF (ORCPT ); Thu, 16 Jun 2016 06:09:05 -0400 Received: from mx2.suse.de ([195.135.220.15]:40534 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753994AbcFPKJB (ORCPT ); Thu, 16 Jun 2016 06:09:01 -0400 Subject: Re: [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is any eligible zone To: Mel Gorman , Andrew Morton , Linux-MM References: <1465495483-11855-1-git-send-email-mgorman@techsingularity.net> <1465495483-11855-12-git-send-email-mgorman@techsingularity.net> Cc: Rik van Riel , Johannes Weiner , LKML From: Vlastimil Babka Message-ID: Date: Thu, 16 Jun 2016 12:08:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <1465495483-11855-12-git-send-email-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2016 08:04 PM, Mel Gorman wrote: > 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. Looks like the code was even wrong before... if classzone_idx wasn't already set to the highmem zone in the first place, it wouldn't look at it. > Signed-off-by: Mel Gorman After fixing the bug below, Acked-by: Vlastimil Babka > --- > mm/vmscan.c | 32 +++++++++++++++++++------------- > 1 file changed, 19 insertions(+), 13 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index e4f3e068b7a0..6663fc75c3bc 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3102,24 +3102,30 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > > sc.nr_reclaimed = 0; > > - /* Scan from the highest requested zone to dma */ > + /* > + * 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) { > + for (i = MAX_NR_ZONES - 1; i >= 0; i++) { i-- > + zone = pgdat->node_zones + i; > + if (!populated_zone(zone)) > + continue; > + > + if (is_highmem_idx(i)) > + classzone_idx = i; > + break; > + } > + } > + > + /* Only reclaim if there are no eligible zones */ > 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 (!zone_balanced(zone, order, 0)) { > + if (!zone_balanced(zone, sc.order, classzone_idx)) { > classzone_idx = i; > break; > } >