From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e7.ny.us.ibm.com (e7.ny.us.ibm.com [32.97.182.137]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id E73C91A054F for ; Sat, 28 Mar 2015 06:28:57 +1100 (AEDT) Received: from /spool/local by e7.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 27 Mar 2015 15:28:55 -0400 Received: from b01cxnp23032.gho.pok.ibm.com (b01cxnp23032.gho.pok.ibm.com [9.57.198.27]) by d01dlp03.pok.ibm.com (Postfix) with ESMTP id 0FB44C90046 for ; Fri, 27 Mar 2015 15:20:03 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t2RJSrX329753568 for ; Fri, 27 Mar 2015 19:28:53 GMT Received: from d01av02.pok.ibm.com (localhost [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t2RJSpRx031944 for ; Fri, 27 Mar 2015 15:28:52 -0400 Date: Fri, 27 Mar 2015 12:28:50 -0700 From: Nishanth Aravamudan To: Mel Gorman 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 Cc: Rik van Riel , anton@sambar.org, linux-kernel@vger.kernel.org, Michal Hocko , linux-mm@kvack.org, Johannes Weiner , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Dan Streetman List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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);