mm: add numa node symlink for memory section in sysfs

Commit c04fc586c (mm: show node to memory section relationship with
symlinks in sysfs) created symlinks from nodes to memory sections, e.g.

/sys/devices/system/node/node1/memory135 -> ../../memory/memory135

If you're examining the memory section though and are wondering what node
it might belong to, you can find it by grovelling around in sysfs, but
it's a little cumbersome.

Add a reverse symlink for each memory section that points back to the
node to which it belongs.

Signed-off-by: Alex Chiang <achiang@hp.com>
Cc: Gary Hade <garyhade@us.ibm.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Greg KH <greg@kroah.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 30 insertions, 6 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
index 9fe91c02ee40..bf1627b02a03 100644
--- a/Documentation/ABI/testing/sysfs-devices-memory
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -60,6 +60,19 @@ Description:
 Users:          hotplug memory remove tools
                 https://w3.opensource.ibm.com/projects/powerpc-utils/
 
+
+What:           /sys/devices/system/memoryX/nodeY
+Date:           October 2009
+Contact:        Linux Memory Management list <linux-mm@kvack.org>
+Description:
+                When CONFIG_NUMA is enabled, a symbolic link that
+                points to the corresponding NUMA node directory.
+
+                For example, the following symbolic link is created for
+                memory section 9 on node0:
+                /sys/devices/system/memory/memory9/node0 -> ../../node/node0
+
+
 What:           /sys/devices/system/node/nodeX/memoryY
 Date:           September 2008
 Contact:        Gary Hade <garyhade@us.ibm.com>
@@ -70,4 +83,3 @@ Description:
                 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 bbc8a6a36921..57e7e9cc1870 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -160,12 +160,15 @@ Under each section, you can see 4 files.
 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:
+If CONFIG_NUMA is enabled the memoryXXX/ 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
 
+A backlink will also be created:
+/sys/devices/system/memory/memory9/node0 -> ../../node/node0
+
 --------------------------------
 4. Physical memory hot-add phase
 --------------------------------
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 54e5d8eaf70e..44eed11bbdf3 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -312,6 +312,7 @@ static int get_nid_for_pfn(unsigned long pfn)
 /* register memory section under specified node if it spans that node */
 int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
 {
+        int ret;
         unsigned long pfn, sect_start_pfn, sect_end_pfn;
 
         if (!mem_blk)
@@ -328,9 +329,15 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
                         continue;
                 if (page_nid != nid)
                         continue;
-                return sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
+                ret = sysfs_create_link_nowarn(&node_devices[nid].sysdev.kobj,
                                         &mem_blk->sysdev.kobj,
                                         kobject_name(&mem_blk->sysdev.kobj));
+                if (ret)
+                        return ret;
+
+                return sysfs_create_link_nowarn(&mem_blk->sysdev.kobj,
+                                &node_devices[nid].sysdev.kobj,
+                                kobject_name(&node_devices[nid].sysdev.kobj));
         }
         /* mem section does not span the specified node */
         return 0;
@@ -359,6 +366,8 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
                         continue;
                 sysfs_remove_link(&node_devices[nid].sysdev.kobj,
                          kobject_name(&mem_blk->sysdev.kobj));
+                sysfs_remove_link(&mem_blk->sysdev.kobj,
+                         kobject_name(&node_devices[nid].sysdev.kobj));
         }
         return 0;
 }