* Nathan Fontenot <nfont@xxxxxxxxxxxxxx> [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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>