Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757998AbZKXIAE (ORCPT ); Tue, 24 Nov 2009 03:00:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757860AbZKXIAD (ORCPT ); Tue, 24 Nov 2009 03:00:03 -0500 Received: from mga10.intel.com ([192.55.52.92]:46087 "EHLO fmsmga102.fm.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757301AbZKXIAC (ORCPT ); Tue, 24 Nov 2009 03:00:02 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.47,275,1257148800"; d="scan'208";a="516812524" Subject: Re: [MM] Make mm counters per cpu instead of atomic From: "Zhang, Yanmin" To: Christoph Lameter Cc: KAMEZAWA Hiroyuki , "hugh.dickins@tiscali.co.uk" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Tejun Heo , Andi Kleen In-Reply-To: References: <1258440521.11321.32.camel@localhost> <1258443101.11321.33.camel@localhost> <1258450465.11321.36.camel@localhost> <1258966270.29789.45.camel@localhost> Content-Type: text/plain; charset="ISO-8859-1" Date: Tue, 24 Nov 2009 16:02:33 +0800 Message-Id: <1259049753.29789.49.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.28.0 (2.28.0-2.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1079 Lines: 23 On Mon, 2009-11-23 at 08:31 -0600, Christoph Lameter wrote: > On Mon, 23 Nov 2009, Zhang, Yanmin wrote: > > > Another theoretic issue is below scenario: > > Process A get the read lock on cpu 0 and is scheduled to cpu 2 to unlock. Then > > it's scheduled back to cpu 0 to repeat the step. eventually, the reader counter > > will overflow. Considering multiple thread cases, it might be faster to > > overflow than what we imagine. When it overflows, processes will hang there. > > True.... We need to find some alternative to per cpu data to scale mmap > sem then. I ran lots of benchmarks such like specjbb2005/hackbench/tbench/dbench/iozone /sysbench_oltp(mysql)/aim7 against percpu tree(based on 2.6.32-rc7) on a 4*8*2 logical cpu machine, and didn't find big result difference between with your patch and without your patch. -- 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/