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Date: Tue, 28 Sep 2010 14:44:40 +0200 From: Avi Kivity <avi@...hat.com> To: Nathan Fontenot <nfont@...tin.ibm.com> CC: linux-kernel@...r.kernel.org, linux-mm@...ck.org, linuxppc-dev@...abs.org, Greg KH <greg@...ah.com>, Dave Hansen <dave@...ux.vnet.ibm.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Subject: Re: [PATCH 0/8] v2 De-Couple sysfs memory directories from memory sections 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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