On 08/12/2010 02:08 PM, Andrew Morton wrote: > On Mon, 09 Aug 2010 12:53:00 -0500 > Nathan Fontenot <nfont@xxxxxxxxxxxxxx> wrote: > >> This set of patches de-couples the idea that there is a single >> directory in sysfs for each memory section. The intent of the >> patches is to reduce the number of sysfs directories created to >> resolve a boot-time performance issue. On very large systems >> boot time are getting very long (as seen on powerpc hardware) >> due to the enormous number of sysfs directories being created. >> On a system with 1 TB of memory we create ~63,000 directories. >> For even larger systems boot times are being measured in hours. > > And those "hours" are mainly due to this problem, I assume. Yes, those hours are spent creating the sysfs directories for each of the memory sections. > >> This set of patches allows for each directory created in sysfs >> to cover more than one memory section. The default behavior for >> sysfs directory creation is the same, in that each directory >> represents a single memory section. A new file 'end_phys_index' >> in each directory contains the physical_id of the last memory >> section covered by the directory so that users can easily >> determine the memory section range of a directory. > > What you're proposing appears to be a non-back-compatible > userspace-visible change. This is a big issue! > > It's not an unresolvable issue, as this is a must-fix problem. But you > should tell us what your proposal is to prevent breakage of existing > installations. A Kconfig option would be good, but a boot-time kernel > command line option which selects the new format would be much better. This shouldn't break existing installations, unless an architecture chooses to do so. With my patch only the powerpc/pseries arch is updated such that what is seen in userspace is different. The default behavior is maintained for all architectures unless they define their own version of memory_block_size_bytes(). The default definition of this routine (defined as __weak in Patch 5/8) sets the memory block size to the same size it currently is, and thus preserving the exisitng 1 sysfs directory per memory section. The only change that will be seen is a new propery for memory section, end_phys_addr, which will have the same value as the existing 'phys_addr' property. > > However you didn't mention this issue at all, and it's the most > important one. > > >> Updates for version 5 of the patchset include the following: >> >> Patch 4/8 Add mutex for add/remove of memory blocks >> - Define the mutex using DEFINE_MUTEX macro. >> >> Patch 8/8 Update memory-hotplug documentation >> - Add information concerning memory holes in phys_index..end_phys_index. > > And you forgot to tell us how long those machines boot with the > patchset applied, which is the entire point of the patchset! Yes, I am working on getting more time on our large systems to get performance numbers with this patch. I'll post them when I get them. -Nathan -- 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>