From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756080Ab0IWSkQ (ORCPT ); Thu, 23 Sep 2010 14:40:16 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:58510 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750855Ab0IWSkO (ORCPT ); Thu, 23 Sep 2010 14:40:14 -0400 Date: Fri, 24 Sep 2010 00:10:02 +0530 From: Balbir Singh To: Nathan Fontenot Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@ozlabs.org, Greg KH , KAMEZAWA Hiroyuki , Dave Hansen Subject: Re: [PATCH 0/8] De-couple sysfs memory directories from memory sections Message-ID: <20100923184002.GM3952@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <4C9A0F8F.2030409@austin.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <4C9A0F8F.2030409@austin.ibm.com> User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Nathan Fontenot [2010-09-22 09:15:43]: > This set of patches decouples the concept that a single memory > section corresponds to a single directory in > /sys/devices/system/memory/. On systems > with large amounts of memory (1+ TB) there are performance issues > related to creating the large number of sysfs directories. For > a powerpc machine with 1 TB of memory we are creating 63,000+ > directories. This is resulting in boot times of around 45-50 > minutes for systems with 1 TB of memory and 8 hours for systems > with 2 TB of memory. With this patch set applied I am now seeing > boot times of 5 minutes or less. > > The root of this issue is in sysfs directory creation. Every time > a directory is created a string compare is done against all sibling > directories to ensure we do not create duplicates. The list of > directory nodes in sysfs is kept as an unsorted list which results > in this being an exponentially longer operation as the number of > directories are created. > > The solution solved by this patch set is to allow a single > directory in sysfs to span multiple memory sections. This is > controlled by an optional architecturally defined function > memory_block_size_bytes(). The default definition of this > routine returns a memory block size equal to the memory section > size. This maintains the current layout of sysfs memory > directories as it appears to userspace to remain the same as it > is today. > > For architectures that define their own version of this routine, > as is done for powerpc in this patchset, the view in userspace > would change such that each memoryXXX directory would span > multiple memory sections. The number of sections spanned would > depend on the value reported by memory_block_size_bytes. > > In both cases a new file 'end_phys_index' is created in each > memoryXXX directory. This file will contain the physical id > of the last memory section covered by the sysfs directory. For > the default case, the value in 'end_phys_index' will be the same > as in the existing 'phys_index' file. > What does this mean for memory hotplug or hotunplug? -- Three Cheers, Balbir