From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id 8185AB70DF for ; Tue, 28 Sep 2010 22:44:56 +1000 (EST) Message-ID: <4CA1E338.6070201@redhat.com> Date: Tue, 28 Sep 2010 14:44:40 +0200 From: Avi Kivity MIME-Version: 1.0 To: Nathan Fontenot Subject: Re: [PATCH 0/8] v2 De-Couple sysfs memory directories from memory sections References: <4CA0EBEB.1030204@austin.ibm.com> In-Reply-To: <4CA0EBEB.1030204@austin.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linuxppc-dev@ozlabs.org, Greg KH , linux-kernel@vger.kernel.org, Dave Hansen , linux-mm@kvack.org, KAMEZAWA Hiroyuki List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 09/27/2010 09:09 PM, Nathan Fontenot wrote: > 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 perfomance 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. > Why not update sysfs directory creation to be fast, for example by using an rbtree instead of a linked list. This fixes an implementation problem in the kernel instead of working around it and creating a new ABI. New ABIs mean old tools won't work, and new tools need to understand both ABIs. -- error compiling committee.c: too many arguments to function