mm: show node to memory section relationship with symlinks in sysfs

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: Gary Hade <garyhade@us.ibm.com>
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 63 insertions, 4 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
index 7a16fe1e2270..9fe91c02ee40 100644
--- a/Documentation/ABI/testing/sysfs-devices-memory
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -6,7 +6,6 @@ Description:
 		internal state of the kernel memory blocks. Files could be
 		added or removed dynamically to represent hot-add/remove
 		operations.
-
 Users:		hotplug memory add/remove tools
 		https://w3.opensource.ibm.com/projects/powerpc-utils/
 
@@ -19,6 +18,56 @@ Description:
 		This is useful for a user-level agent to determine
 		identify removable sections of the memory before attempting
 		potentially expensive hot-remove memory operation
+Users:		hotplug memory remove tools
+		https://w3.opensource.ibm.com/projects/powerpc-utils/
+
+What:		/sys/devices/system/memory/memoryX/phys_device
+Date:		September 2008
+Contact:	Badari Pulavarty <pbadari@us.ibm.com>
+Description:
+		The file /sys/devices/system/memory/memoryX/phys_device
+		is read-only and is designed to show the name of physical
+		memory device.  Implementation is currently incomplete.
 
+What:		/sys/devices/system/memory/memoryX/phys_index
+Date:		September 2008
+Contact:	Badari Pulavarty <pbadari@us.ibm.com>
+Description:
+		The file /sys/devices/system/memory/memoryX/phys_index
+		is read-only and contains the section ID in hexadecimal
+		which is equivalent to decimal X contained in the
+		memory section directory name.
+
+What:		/sys/devices/system/memory/memoryX/state
+Date:		September 2008
+Contact:	Badari Pulavarty <pbadari@us.ibm.com>
+Description:
+		The file /sys/devices/system/memory/memoryX/state
+		is read-write.  When read, it's contents show the
+		online/offline state of the memory section.  When written,
+		root can toggle the the online/offline state of a removable
+		memory section (see removable file description above)
+		using the following commands.
+		# echo online > /sys/devices/system/memory/memoryX/state
+		# echo offline > /sys/devices/system/memory/memoryX/state
+
+		For example, if /sys/devices/system/memory/memory22/removable
+		contains a value of 1 and
+		/sys/devices/system/memory/memory22/state contains the
+		string "online" the following command can be executed by
+		by root to offline that section.
+		# echo offline > /sys/devices/system/memory/memory22/state
 Users:		hotplug memory remove tools
 		https://w3.opensource.ibm.com/projects/powerpc-utils/
+
+What:		/sys/devices/system/node/nodeX/memoryY
+Date:		September 2008
+Contact:	Gary Hade <garyhade@us.ibm.com>
+Description:
+		When CONFIG_NUMA is enabled
+		/sys/devices/system/node/nodeX/memoryY is a symbolic link that
+		points to the corresponding /sys/devices/system/memory/memoryY
+		memory section directory.  For example, the following symbolic
+		link is created for memory section 9 on node0.
+		/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
+
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index 168117bd6ee8..4c2ecf537a4a 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -124,7 +124,7 @@ config options.
     This option can be kernel module too.
 
 --------------------------------
-3 sysfs files for memory hotplug
+4 sysfs files for memory hotplug
 --------------------------------
 All sections have their device information under /sys/devices/system/memory as
 
@@ -138,11 +138,12 @@ For example, assume 1GiB section size. A device for a memory starting at
 (0x100000000 / 1Gib = 4)
 This device covers address range [0x100000000 ... 0x140000000)
 
-Under each section, you can see 3 files.
+Under each section, you can see 4 files.
 
 /sys/devices/system/memory/memoryXXX/phys_index
 /sys/devices/system/memory/memoryXXX/phys_device
 /sys/devices/system/memory/memoryXXX/state
+/sys/devices/system/memory/memoryXXX/removable
 
 'phys_index' : read-only and contains section id, same as XXX.
 'state'      : read-write
@@ -150,10 +151,20 @@ Under each section, you can see 3 files.
                at write: user can specify "online", "offline" command
 'phys_device': read-only: designed to show the name of physical memory device.
                This is not well implemented now.
+'removable'  : read-only: contains an integer value indicating
+               whether the memory section is removable or not
+               removable.  A value of 1 indicates that the memory
+               section is removable and a value of 0 indicates that
+               it is not removable.
 
 NOTE:
   These directories/files appear after physical memory hotplug phase.
 
+If CONFIG_NUMA is enabled the
+/sys/devices/system/memory/memoryXXX memory section
+directories can also be accessed via symbolic links located in
+the /sys/devices/system/node/node* directories.  For example:
+/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
 
 --------------------------------
 4. Physical memory hot-add phase
@@ -365,7 +376,6 @@ node if necessary.
   - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
     sysctl or new control file.
   - showing memory section and physical device relationship.
-  - showing memory section and node relationship (maybe good for NUMA)
   - showing memory section is under ZONE_MOVABLE or not
   - test and make it better memory offlining.
   - support HugeTLB page migration and offlining.