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Subject[RFC][PATCH v2 08/21] mm: introduce and export pgdat peer_node
From: Fan Du <fan.du@intel.com>

Each CPU socket can have 1 DRAM and 1 PMEM node, we call them "peer nodes".
Migration between DRAM and PMEM will by default happen between peer nodes.

It's a temp solution. In multiple memory layers, a node can have both
promotion and demotion targets instead of a single peer node. User space
may also be able to infer promotion/demotion targets based on future
HMAT info.

Signed-off-by: Fan Du <fan.du@intel.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
---
drivers/base/node.c | 11 +++++++++++
include/linux/mmzone.h | 12 ++++++++++++
mm/page_alloc.c | 29 +++++++++++++++++++++++++++++
3 files changed, 52 insertions(+)

--- linux.orig/drivers/base/node.c 2018-12-23 19:39:51.647261099 +0800
+++ linux/drivers/base/node.c 2018-12-23 19:39:51.643261112 +0800
@@ -242,6 +242,16 @@ static ssize_t type_show(struct device *
}
static DEVICE_ATTR(type, S_IRUGO, type_show, NULL);

+static ssize_t peer_node_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ int nid = dev->id;
+ struct pglist_data *pgdat = NODE_DATA(nid);
+
+ return sprintf(buf, "%d\n", pgdat->peer_node);
+}
+static DEVICE_ATTR(peer_node, S_IRUGO, peer_node_show, NULL);
+
static struct attribute *node_dev_attrs[] = {
&dev_attr_cpumap.attr,
&dev_attr_cpulist.attr,
@@ -250,6 +260,7 @@ static struct attribute *node_dev_attrs[
&dev_attr_distance.attr,
&dev_attr_vmstat.attr,
&dev_attr_type.attr,
+ &dev_attr_peer_node.attr,
NULL
};
ATTRIBUTE_GROUPS(node_dev);
--- linux.orig/include/linux/mmzone.h 2018-12-23 19:39:51.647261099 +0800
+++ linux/include/linux/mmzone.h 2018-12-23 19:39:51.643261112 +0800
@@ -713,6 +713,18 @@ typedef struct pglist_data {
/* Per-node vmstats */
struct per_cpu_nodestat __percpu *per_cpu_nodestats;
atomic_long_t vm_stat[NR_VM_NODE_STAT_ITEMS];
+
+ /*
+ * Points to the nearest node in terms of latency
+ * E.g. peer of node 0 is node 2 per SLIT
+ * node distances:
+ * node 0 1 2 3
+ * 0: 10 21 17 28
+ * 1: 21 10 28 17
+ * 2: 17 28 10 28
+ * 3: 28 17 28 10
+ */
+ int peer_node;
} pg_data_t;

#define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages)
--- linux.orig/mm/page_alloc.c 2018-12-23 19:39:51.647261099 +0800
+++ linux/mm/page_alloc.c 2018-12-23 19:39:51.643261112 +0800
@@ -6926,6 +6926,34 @@ static void check_for_memory(pg_data_t *
}
}

+/*
+ * Return the nearest peer node in terms of *locality*
+ * E.g. peer of node 0 is node 2 per SLIT
+ * node distances:
+ * node 0 1 2 3
+ * 0: 10 21 17 28
+ * 1: 21 10 28 17
+ * 2: 17 28 10 28
+ * 3: 28 17 28 10
+ */
+static int find_best_peer_node(int nid)
+{
+ int n, val;
+ int min_val = INT_MAX;
+ int peer = NUMA_NO_NODE;
+
+ for_each_online_node(n) {
+ if (n == nid)
+ continue;
+ val = node_distance(nid, n);
+ if (val < min_val) {
+ min_val = val;
+ peer = n;
+ }
+ }
+ return peer;
+}
+
/**
* free_area_init_nodes - Initialise all pg_data_t and zone data
* @max_zone_pfn: an array of max PFNs for each zone
@@ -7012,6 +7040,7 @@ void __init free_area_init_nodes(unsigne
if (pgdat->node_present_pages)
node_set_state(nid, N_MEMORY);
check_for_memory(pgdat, nid);
+ pgdat->peer_node = find_best_peer_node(nid);
}
}


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