Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752804AbbDCSYu (ORCPT ); Fri, 3 Apr 2015 14:24:50 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:35762 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751186AbbDCSYs (ORCPT ); Fri, 3 Apr 2015 14:24:48 -0400 Date: Fri, 3 Apr 2015 20:24:45 +0200 From: Michal Hocko To: Nishanth Aravamudan Cc: Dave Hansen , Mel Gorman , anton@sambar.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Johannes Weiner , Rik van Riel , Dan Streetman Subject: Re: [PATCH v2] mm: vmscan: do not throttle based on pfmemalloc reserves if node has no reclaimable pages Message-ID: <20150403182445.GA31900@dhcp22.suse.cz> References: <20150327192850.GA18701@linux.vnet.ibm.com> <5515BAF7.6070604@intel.com> <20150327222350.GA22887@linux.vnet.ibm.com> <20150331094829.GE9589@dhcp22.suse.cz> <20150403174357.GE32318@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150403174357.GE32318@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 Content-Length: 1880 Lines: 44 On Fri 03-04-15 10:43:57, Nishanth Aravamudan wrote: > On 31.03.2015 [11:48:29 +0200], Michal Hocko wrote: [...] > > I would expect kswapd would be looping endlessly because the zone > > wouldn't be balanced obviously. But I would be wrong... because > > pgdat_balanced is doing this: > > /* > > * A special case here: > > * > > * balance_pgdat() skips over all_unreclaimable after > > * DEF_PRIORITY. Effectively, it considers them balanced so > > * they must be considered balanced here as well! > > */ > > if (!zone_reclaimable(zone)) { > > balanced_pages += zone->managed_pages; > > continue; > > } > > > > and zone_reclaimable is false for you as you didn't have any > > zone_reclaimable_pages(). But wakeup_kswapd doesn't do this check so it > > would see !zone_balanced() AFAICS (build_zonelists doesn't ignore those > > zones right?) and so the kswapd would be woken up easily. So it looks > > like a mess. > > My understanding, and I could easily be wrong, is that kswapd2 (node 2 > is the exhausted one) spins endlessly, because the reclaim logic sees > that we are reclaiming from somewhere but the allocation request for > node 2 (which is __GFP_THISNODE for hugepages, not GFP_THISNODE) will > never complete, so we just continue to reclaim. __GFP_THISNODE would be waking up kswapd2 again and again, that is true. I am just wondering whether we will have any __GFP_THISNODE allocations for a node without CPUs (numa_node_id() shouldn't return such a node AFAICS). Maybe if somebody is bound to Node2 explicitly but I would consider this as a misconfiguration. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/