[PATCH v3 2/7] mm: demotion: Add new node state N_DEMOTION_TARGETS

[Jagdish Gediya <jvgediya@linux.ibm.com>]

Some systems(e.g. PowerVM) have DRAM(fast memory) only NUMA node
which are N_MEMORY as well as slow memory(persistent memory) only
NUMA node which are also N_MEMORY. As the current demotion target
finding algorithm works based on N_MEMORY and best distance, it can
choose DRAM only NUMA node as demotion target instead of persistent
memory node on such systems. If DRAM only NUMA node is filled with
demoted pages then at some point new allocations can start falling
to persistent memory, so basically cold pages are in fast memory
(due to demotion) and new pages are in slow memory, this is why
persistent memory nodes should be utilized for demotion and dram node
should be avoided for demotion so that they can be used for new
allocations.

Add new state N_DEMOTION_TARGETS, node_states[N_DEMOTION_TARGETS]
then can be used to hold the list of nodes which can be used
as demotion targets, later patches in the series builds demotion
targets based on nodes available in node_states[N_DEMOTION_TARGETS].

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
---
 drivers/base/node.c      | 4 ++++
 include/linux/nodemask.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index ec8bb24a5a22..6eef22e6413e 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -1038,6 +1038,9 @@ static struct node_attr node_state_attr[] = {
 	[N_CPU] = _NODE_ATTR(has_cpu, N_CPU),
 	[N_GENERIC_INITIATOR] = _NODE_ATTR(has_generic_initiator,
 					   N_GENERIC_INITIATOR),
+	[N_DEMOTION_TARGETS] = _NODE_ATTR(demotion_targets,
+					  N_DEMOTION_TARGETS),
+
 };
 
 static struct attribute *node_state_attrs[] = {
@@ -1050,6 +1053,7 @@ static struct attribute *node_state_attrs[] = {
 	&node_state_attr[N_MEMORY].attr.attr,
 	&node_state_attr[N_CPU].attr.attr,
 	&node_state_attr[N_GENERIC_INITIATOR].attr.attr,
+	&node_state_attr[N_DEMOTION_TARGETS].attr.attr,
 	NULL
 };
 
diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index 567c3ddba2c4..17844300fd57 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -400,6 +400,7 @@ enum node_states {
 	N_MEMORY,		/* The node has memory(regular, high, movable) */
 	N_CPU,		/* The node has one or more cpus */
 	N_GENERIC_INITIATOR,	/* The node has one or more Generic Initiators */
+	N_DEMOTION_TARGETS,	/* Nodes that should be considered as demotion targets */
 	NR_NODE_STATES
 };
 
-- 
2.35.1