• Gary Hade's avatar
    mm: show node to memory section relationship with symlinks in sysfs · c04fc586
    Gary Hade authored
    Show node to memory section relationship with symlinks in sysfs
    
    Add /sys/devices/system/node/nodeX/memoryY symlinks for all
    the memory sections located on nodeX.  For example:
    /sys/devices/system/node/node1/memory135 -> ../../memory/memory135
    indicates that memory section 135 resides on node1.
    
    Also revises documentation to cover this change as well as updating
    Documentation/ABI/testing/sysfs-devices-memory to include descriptions
    of memory hotremove files 'phys_device', 'phys_index', and 'state'
    that were previously not described there.
    
    In addition to it always being a good policy to provide users with
    the maximum possible amount of physical location information for
    resources that can be hot-added and/or hot-removed, the following
    are some (but likely not all) of the user benefits provided by
    this change.
    Immediate:
      - Provides information needed to determine the specific node
        on which a defective DIMM is located.  This will reduce system
        downtime when the node or defective DIMM is swapped out.
      - Prevents unintended onlining of a memory section that was
        previously offlined due to a defective DIMM.  This could happen
        during node hot-add when the user or node hot-add assist script
        onlines _all_ offlined sections due to user or script inability
        to identify the specific memory sections located on the hot-added
        node.  The consequences of reintroducing the defective memory
        could be ugly.
      - Provides information needed to vary the amount and distribution
        of memory on specific nodes for testing or debugging purposes.
    Future:
      - Will provide information needed to identify the memory
        sections that need to be offlined prior to physical removal
        of a specific node.
    
    Symlink creation during boot was tested on 2-node x86_64, 2-node
    ppc64, and 2-node ia64 systems.  Symlink creation during physical
    memory hot-add tested on a 2-node x86_64 system.
    Signed-off-by: default avatarGary Hade <garyhade@us.ibm.com>
    Signed-off-by: default avatarBadari Pulavarty <pbadari@us.ibm.com>
    Acked-by: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c04fc586
memory.h 2.96 KB