v5 De-couple sysfs memory directories from memory sections

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.

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.

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.

Thanks,

Nathan Fontenot

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