[PATCH] mm/demotion: Add sysfs ABI documentation

[Aneesh Kumar K.V]

Add sysfs ABI documentation.

Suggested-by: Wei Xu <weixugc@xxxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
 .../ABI/testing/sysfs-kernel-mm-memory-tiers  | 81 +++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers b/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
new file mode 100644
index 000000000000..41b0d1756ddb
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
@@ -0,0 +1,81 @@
+What:		/sys/devices/system/memtier/
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+		This is the directory containing the information about memory tiers.
+
+		Each memory tier has its own subdirectory.
+
+		The order of memory tiers is determined by their rank values, not by
+		their memtier device names.  A higher rank value means a higher tier.
+
+What:		/sys/devices/system/memtier/default_tier
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+		The default memory tier to which memory would get added via hotplug
+		if the NUMA node is not part of any memory tier.
+
+What:		/sys/devices/system/memtier/max_tier
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+		The max memory tier device ID we can create. Users can create memory
+		tiers in range [0 - max_tier)
+
+What:		/sys/devices/system/memtier/memtierN/
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+		This is the directory containing the information about a particular
+		memory tier, memtierN, where N is the memtier device ID (e.g. 0, 1).
+
+		The memtier device ID number itself is just an identifier and has no
+		special meaning, i.e. memtier device ID numbers do not determine the
+		order of memory tiers.
+
+What:		/sys/devices/system/memtier/memtierN/rank
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+
+		When read, list the "rank" value associated with memtierN.
+
+		"Rank" is an opaque value. Its absolute value doesn't have any
+		special meaning. But the rank values of different memtiers can be
+		compared with each other to determine the memory tier order.
+
+		For example, if we have 3 memtiers: memtier0, memtier1, memiter2, and
+		their rank values are 100, 10, 50, then the memory tier order is:
+		memtier0 -> memtier2 -> memtier1, where memtier0 is the highest tier
+		and memtier1 is the lowest tier.
+
+		The rank value of each memtier should be unique.
+
+What:		/sys/devices/system/memtier/memtierN/nodelist
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+
+		When read, list the memory nodes in the specified tier.
+
+What:		/sys/devices/system/node/nodeN/memtier
+Date:		Jun 2022
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for tiered memory
+
+		When read, list the device ID of the memory tier that the node belongs
+		to.  Its value is empty for a CPU-only NUMA node.
+
+		When written, the kernel moves the node into the specified memory
+		tier if the move is allowed. The tier assignments of all other
+		nodes are not affected.
+
+		When written with the special string "none" the specific node is removed
+		from participating in memory demotion.
-- 
2.36.1