From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753370Ab2GZVan (ORCPT ); Thu, 26 Jul 2012 17:30:43 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:40055 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753304Ab2GZVad (ORCPT ); Thu, 26 Jul 2012 17:30:33 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Shaohua Li , Mel Gorman , Minchan Kim Subject: [ 11/40] vmscan: clear ZONE_CONGESTED for zone with good watermark Date: Thu, 26 Jul 2012 14:29:29 -0700 Message-Id: <20120726211412.097882882@linuxfoundation.org> X-Mailer: git-send-email 1.7.10.1.362.g242cab3 In-Reply-To: <20120726211411.164006056@linuxfoundation.org> References: <20120726211424.GA7709@kroah.com> <20120726211411.164006056@linuxfoundation.org> User-Agent: quilt/0.60-20.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Greg KH 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shaohua Li commit 439423f6894aa0dec22187526827456f5004baed upstream. Stable note: Not tracked in Bugzilla. kswapd is responsible for clearing ZONE_CONGESTED after it balances a zone and this patch fixes a bug where that was failing to happen. Without this patch, processes can stall in wait_iff_congested unnecessarily. For users, this can look like an interactivity stall but some workloads would see it as sudden drop in throughput. ZONE_CONGESTED is only cleared in kswapd, but pages can be freed in any task. It's possible ZONE_CONGESTED isn't cleared in some cases: 1. the zone is already balanced just entering balance_pgdat() for order-0 because concurrent tasks free memory. In this case, later check will skip the zone as it's balanced so the flag isn't cleared. 2. high order balance fallbacks to order-0. quote from Mel: At the end of balance_pgdat(), kswapd uses the following logic; If reclaiming at high order { for each zone { if all_unreclaimable skip if watermark is not met order = 0 loop again /* watermark is met */ clear congested } } i.e. it clears ZONE_CONGESTED if it the zone is balanced. if not, it restarts balancing at order-0. However, if the higher zones are balanced for order-0, kswapd will miss clearing ZONE_CONGESTED as that only happens after a zone is shrunk. This can mean that wait_iff_congested() stalls unnecessarily. This patch makes kswapd clear ZONE_CONGESTED during its initial highmem->dma scan for zones that are already balanced. Signed-off-by: Shaohua Li Acked-by: Mel Gorman Reviewed-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman --- mm/vmscan.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2456,6 +2456,9 @@ loop_again: high_wmark_pages(zone), 0, 0)) { end_zone = i; break; + } else { + /* If balanced, clear the congested flag */ + zone_clear_flag(zone, ZONE_CONGESTED); } } if (i < 0)