From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752301Ab1GSHJb (ORCPT ); Tue, 19 Jul 2011 03:09:31 -0400 Received: from mga03.intel.com ([143.182.124.21]:12618 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751551Ab1GSHJ3 (ORCPT ); Tue, 19 Jul 2011 03:09:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,227,1309762800"; d="scan'208";a="28819251" Subject: [PATCH]vmscan: fix a livelock in kswapd From: Shaohua Li To: Andrew Morton Cc: mgorman@suse.de, linux-mm , lkml Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Jul 2011 15:09:27 +0800 Message-ID: <1311059367.15392.299.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I'm running a workload which triggers a lot of swap in a machine with 4 nodes. After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or kswapd2 are keeping running and I can't access filesystem, but most memory is free. This looks like a regression since commit 08951e545918c159. Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if all zones have watermark ok, end_zone will keep 0. Later sleeping_prematurely() always returns true. Because this is an order 3 wakeup, and if classzone_idx is 0, both balanced_pages and present_pages in pgdat_balanced() are 0. We add a special case here. If a zone has no page, we think it's balanced. This fixes the livelock. Signed-off-by: Shaohua Li diff --git a/mm/vmscan.c b/mm/vmscan.c index 5ed24b9..ad4056f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2310,7 +2310,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages, for (i = 0; i <= classzone_idx; i++) present_pages += pgdat->node_zones[i].present_pages; - return balanced_pages > (present_pages >> 2); + /* A special case here: if zone has no page, we think it's balanced */ + return balanced_pages >= (present_pages >> 2); } /* is kswapd sleeping prematurely? */