From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755156AbcH3PA7 (ORCPT ); Tue, 30 Aug 2016 11:00:59 -0400 Received: from outbound-smtp02.blacknight.com ([81.17.249.8]:45401 "EHLO outbound-smtp02.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753135AbcH3PA5 (ORCPT ); Tue, 30 Aug 2016 11:00:57 -0400 Date: Tue, 30 Aug 2016 16:00:51 +0100 From: Mel Gorman To: Srikar Dronamraju Cc: Andrew Morton , Linux-MM , Rik van Riel , Vlastimil Babka , Johannes Weiner , Minchan Kim , Joonsoo Kim , LKML , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Mahesh Salgaonkar , Hari Bathini Subject: Re: [PATCH 07/34] mm, vmscan: make kswapd reclaim in terms of nodes Message-ID: <20160830150051.GW8119@techsingularity.net> References: <1467970510-21195-1-git-send-email-mgorman@techsingularity.net> <1467970510-21195-8-git-send-email-mgorman@techsingularity.net> <20160829093844.GA2592@linux.vnet.ibm.com> <20160830120728.GV8119@techsingularity.net> <20160830142508.GA10514@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20160830142508.GA10514@linux.vnet.ibm.com> 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, Aug 30, 2016 at 07:55:08PM +0530, Srikar Dronamraju wrote: > > > > > > This patch seems to hurt FA_DUMP functionality. This behaviour is not > > > seen on v4.7 but only after this patch. > > > > > > So when a kernel on a multinode machine with memblock_reserve() such > > > that most of the nodes have zero available memory, kswapd seems to be > > > consuming 100% of the time. > > > > > > > Why is FA_DUMP specifically the trigger? If the nodes have zero available > > memory then is the zone_populated() check failing when FA_DUMP is enabled? If > > so, that would both allow kswapd to wake and stay awake. > > > > The trigger is memblock_reserve() for the complete node memory. And > this is exactly what FA_DUMP does. Here again the node has memory but > its all reserved so there is no free memory in the node. > > Did you mean populated_zone() when you said zone_populated or have I > mistaken? populated_zone() does return 1 since it checks for > zone->present_pages. > Yes, I meant populated_zone(). Using present pages may have hidden a long-lived corner case as it was unexpected that an entire node would be reserved. The old code happened to survive *probably* because pgdat_reclaimable would look false and kswapd checks for pgdat being balanced would happen to do the right thing in this case. Can you check if something like this works? diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index d572b78b65e1..cf64a5456cf6 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -830,7 +830,7 @@ unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long); static inline int populated_zone(struct zone *zone) { - return (!!zone->present_pages); + return (!!zone->managed_pages); } extern int movable_zone; -- Mel Gorman SUSE Labs