From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754780AbcGEKiM (ORCPT ); Tue, 5 Jul 2016 06:38:12 -0400 Received: from outbound-smtp08.blacknight.com ([46.22.139.13]:46822 "EHLO outbound-smtp08.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752103AbcGEKiL (ORCPT ); Tue, 5 Jul 2016 06:38:11 -0400 Date: Tue, 5 Jul 2016 11:38:06 +0100 From: Mel Gorman To: Minchan Kim Cc: Andrew Morton , Linux-MM , Rik van Riel , Vlastimil Babka , Johannes Weiner , LKML Subject: Re: [PATCH 11/31] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Message-ID: <20160705103806.GH11498@techsingularity.net> References: <1467403299-25786-1-git-send-email-mgorman@techsingularity.net> <1467403299-25786-12-git-send-email-mgorman@techsingularity.net> <20160705061117.GD28164@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20160705061117.GD28164@bbox> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 05, 2016 at 03:11:17PM +0900, Minchan Kim wrote: > > - if (i < 0) > > - goto out; > > + /* > > + * Only reclaim if there are no eligible zones. Check from > > + * high to low zone to avoid prematurely clearing pgdat > > + * congested state. > > I cannot understand "prematurely clearing pgdat congested state". > Could you add more words to clear it out? > It's surprisingly difficult to concisely explain. Is this any better? /* * 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)) > > If buffer_head is over limit, old logic force to reclaim highmem but > this zone_balanced logic will prevent it. > The old logic was always busted on 64-bit because is_highmem would always be 0. The original intent appears to be that buffer_heads_over_limit would release the buffers when pages went inactive. There are a number of things we treated inconsistently that get fixed up in the series and buffer_heads_over_limit is one of them. -- Mel Gorman SUSE Labs