Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751670Ab0F1EPk (ORCPT ); Mon, 28 Jun 2010 00:15:40 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:51838 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750838Ab0F1EPj (ORCPT ); Mon, 28 Jun 2010 00:15:39 -0400 To: KOSAKI Motohiro Cc: Nathan Fontenot , Andi Kleen , linux-kernel@vger.kernel.org, Greg Kroah-Hartman References: <87d3vfeage.fsf@basil.nowhere.org> <4C24C279.3050206@austin.ibm.com> <20100628110658.387B.A69D9226@jp.fujitsu.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: Sun, 27 Jun 2010 21:15:29 -0700 In-Reply-To: <20100628110658.387B.A69D9226@jp.fujitsu.com> (KOSAKI Motohiro's message of "Mon\, 28 Jun 2010 11\:20\:27 +0900 \(JST\)") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in02.mta.xmission.com;;;ip=67.188.5.249;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 67.188.5.249 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa04 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;KOSAKI Motohiro X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [PATCH] memory hotplug disable boot option X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1923 Lines: 41 KOSAKI Motohiro writes: >> On 06/25/2010 04:19 AM, Andi Kleen wrote: >> > KOSAKI Motohiro writes: >> > >> >>> Proposed patch to disable memory hotplug via a boot option, >> >>> mem_hotplug=[on|off]. The patch only disables memory hotplug in that it >> >>> prevents the creation of the memory sysfs directories for memory sections. >> >>> >> >>> This patch is meant to help alleviate very long boot times on systems with >> >>> large memory (1+ TB) and many memory sections (10's of thousands). >> >> >> >> Why making simple /sys file is so slowly? Couldn't we fix such performance >> >> problem? >> >> The issue is the large number of sysfs memory directories that get created. >> On a system with 1 TB of memory I am seeing ~63,00 directories. The long >> creation time is due to the string compare check in sysfs code to ensure >> we are not creating a directory with a duplicate name. > > Ah, I see. probably this is sysfs issue. So Let's cc Greg and Eric. > Greg, I have dumb question. Why sysfs call strcmp() so heavily? I mean why sysfs > don't have hash based name dupliation check? Simplicity of the current implementation. I have a prototype patch sitting around somewhere. I think ultimately it makes sense to do something like extN's htree directory structure in sysfs. I wanted to get the tagged sysfs support in before I worked on scalability because that slightly changes the requirements. Improving the scalability here is certainly worth doing, but I am slightly concerned there is something else algorithmically wrong if this is still going to take 33 minutes to boot with 2TB. Eric -- 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/