On 09/28/2010 07:38 AM, Robin Holt wrote: > I was tasked with looking at a slowdown in similar sized SGI machines > booting x86_64. Jack Steiner had already looked into the memory_dev_init. > I was looking at link_mem_sections(). > > I made a dramatic improvement on a 16TB machine in that function by > merely caching the most recent memory section and checking to see if > the next memory section happens to be the subsequent in the linked list > of kobjects. > > That simple cache reduced the time for link_mem_sections from 1 hour 27 > minutes down to 46 seconds. Nice! > > I would like to propose we implement something along those lines also, > but I am currently swamped. I can probably get you a patch tomorrow > afternoon that applies at the end of this set. Should this be done as a separate patch? This patch set concentrates on updates to the memory code with the node updates only being done due to the memory changes. I think its a good idea to do the caching and have no problem adding on to this patchset if no one else has any objections. -Nathan > > Thanks, > Robin > > On Mon, Sep 27, 2010 at 02:09:31PM -0500, 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. >> >> 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. >> >> This version of the patch set includes an update to to properly >> report block_size_bytes, phys_index, and end_phys_index. Additionally, >> the patch that adds the end_phys_index sysfs file is now patch 5/8 >> instead of being patch 2/8 as in the previous version of the patches. >> >> -Nathan Fontenot >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ -- 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>