From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754005AbbC0T3E (ORCPT ); Fri, 27 Mar 2015 15:29:04 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:52789 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752673AbbC0T26 (ORCPT ); Fri, 27 Mar 2015 15:28:58 -0400 Date: Fri, 27 Mar 2015 12:28:50 -0700 From: Nishanth Aravamudan To: Mel Gorman Cc: anton@sambar.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Johannes Weiner , Michal Hocko , Rik van Riel , Dan Streetman Subject: [PATCH] mm: vmscan: do not throttle based on pfmemalloc reserves if node has no reclaimable zones Message-ID: <20150327192850.GA18701@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Operating-System: Linux 3.13.0-40-generic (x86_64) User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15032719-0033-0000-0000-000004115DBD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Based upon 675becce15 ("mm: vmscan: do not throttle based on pfmemalloc reserves if node has no ZONE_NORMAL") from Mel. We have a system with the following topology: (0) root @ br30p03: /root # numactl -H available: 3 nodes (0,2-3) node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 node 0 size: 28273 MB node 0 free: 27323 MB node 2 cpus: node 2 size: 16384 MB node 2 free: 0 MB node 3 cpus: 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 node 3 size: 30533 MB node 3 free: 13273 MB node distances: node 0 2 3 0: 10 20 20 2: 20 10 20 3: 20 20 10 Node 2 has no free memory, because: # cat /sys/devices/system/node/node2/hugepages/hugepages-16777216kB/nr_hugepages 1 This leads to the following zoneinfo: Node 2, zone DMA pages free 0 min 1840 low 2300 high 2760 scanned 0 spanned 262144 present 262144 managed 262144 ... all_unreclaimable: 1 If one then attempts to allocate some normal 16M hugepages: echo 37 > /proc/sys/vm/nr_hugepages The echo enver returns and kswapd2 consumes CPU cycles. This is because throttle_direct_reclaim ends up calling wait_event(pfmemalloc_wait, pfmemalloc_watermark_ok...). pfmemalloc_watermark_ok() in turn checks all zones on the node and see if the there are any reserves, and if so, then indicates the watermarks are ok, by seeing if there are sufficient free pages. 675becce15 added a condition already for memoryless nodes. In this case, though, the node has memory, it is just all consumed (and not recliamable). Effectively, though, the result is the same on this call to pfmemalloc_watermark_ok() and thus seems like a reasonable additional condition. With this change, the afore-mentioned 16M hugepage allocation succeeds and correctly round-robins between Nodes 1 and 3. Signed-off-by: Nishanth Aravamudan diff --git a/mm/vmscan.c b/mm/vmscan.c index dcd90c8..033c2b7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2585,7 +2585,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat) for (i = 0; i <= ZONE_NORMAL; i++) { zone = &pgdat->node_zones[i]; - if (!populated_zone(zone)) + if (!populated_zone(zone) || !zone_reclaimable(zone)) continue; pfmemalloc_reserve += min_wmark_pages(zone);