From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754797AbcGLOfi (ORCPT ); Tue, 12 Jul 2016 10:35:38 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:51736 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755040AbcGLO3W (ORCPT ); Tue, 12 Jul 2016 10:29:22 -0400 Date: Tue, 12 Jul 2016 10:29:09 -0400 From: Johannes Weiner To: Mel Gorman Cc: Andrew Morton , Linux-MM , Rik van Riel , Vlastimil Babka , Minchan Kim , Joonsoo Kim , LKML Subject: Re: [PATCH 12/34] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Message-ID: <20160712142909.GF5881@cmpxchg.org> References: <1467970510-21195-1-git-send-email-mgorman@techsingularity.net> <1467970510-21195-13-git-send-email-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1467970510-21195-13-git-send-email-mgorman@techsingularity.net> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 08, 2016 at 10:34:48AM +0100, 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. > > [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 > Signed-off-by: Mel Gorman > Signed-off-by: Hillf Danton > Acked-by: Vlastimil Babka Acked-by: Johannes Weiner One and a half observations: > @@ -3144,31 +3144,39 @@ 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 */ > - 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. The mention of highmem in this comment make only sense within the context of this diff; it'll be pretty confusing in the standalone code. Also, double "it is" :)