Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752175Ab3GSUzr (ORCPT ); Fri, 19 Jul 2013 16:55:47 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:50541 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751812Ab3GSUzn (ORCPT ); Fri, 19 Jul 2013 16:55:43 -0400 From: Johannes Weiner To: Andrew Morton Cc: Mel Gorman , Rik van Riel , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [patch 1/3] mm: vmscan: fix numa reclaim balance problem in kswapd Date: Fri, 19 Jul 2013 16:55:23 -0400 Message-Id: <1374267325-22865-2-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 1.8.3.2 In-Reply-To: <1374267325-22865-1-git-send-email-hannes@cmpxchg.org> References: <1374267325-22865-1-git-send-email-hannes@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1839 Lines: 48 When the page allocator fails to get a page from all zones in its given zonelist, it wakes up the per-node kswapds for all zones that are at their low watermark. However, with a system under load and the free page counters being per-cpu approximations, the observed counter value in a zone can fluctuate enough that the allocation fails but the kswapd wakeup is also skipped while the zone is still really close to the low watermark. When one node misses a wakeup like this, it won't be aged before all the other node's zones are down to their low watermarks again. And skipping a full aging cycle is an obvious fairness problem. Kswapd runs until the high watermarks are restored, so it should also be woken when the high watermarks are not met. This ages nodes more equally and creates a safety margin for the page counter fluctuation. By using zone_balanced(), it will now check, in addition to the watermark, if compaction requires more order-0 pages to create a higher order page. Signed-off-by: Johannes Weiner --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index e364542..bccc6d3 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3277,7 +3277,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) } if (!waitqueue_active(&pgdat->kswapd_wait)) return; - if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) + if (zone_balanced(zone, order, 0, 0)) return; trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); -- 1.8.3.2 -- 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/