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-rw-r--r--Documentation/admin-guide/numastat.rst31
1 files changed, 28 insertions, 3 deletions
diff --git a/Documentation/admin-guide/numastat.rst b/Documentation/admin-guide/numastat.rst
index aaf1667489f8..08ec2c2bdce3 100644
--- a/Documentation/admin-guide/numastat.rst
+++ b/Documentation/admin-guide/numastat.rst
@@ -6,6 +6,21 @@ Numa policy hit/miss statistics
All units are pages. Hugepages have separate counters.
+The numa_hit, numa_miss and numa_foreign counters reflect how well processes
+are able to allocate memory from nodes they prefer. If they succeed, numa_hit
+is incremented on the preferred node, otherwise numa_foreign is incremented on
+the preferred node and numa_miss on the node where allocation succeeded.
+
+Usually preferred node is the one local to the CPU where the process executes,
+but restrictions such as mempolicies can change that, so there are also two
+counters based on CPU local node. local_node is similar to numa_hit and is
+incremented on allocation from a node by CPU on the same node. other_node is
+similar to numa_miss and is incremented on the node where allocation succeeds
+from a CPU from a different node. Note there is no counter analogical to
+numa_foreign.
+
+In more detail:
+
=============== ============================================================
numa_hit A process wanted to allocate memory from this node,
and succeeded.
@@ -14,11 +29,13 @@ numa_miss A process wanted to allocate memory from another node,
but ended up with memory from this node.
numa_foreign A process wanted to allocate on this node,
- but ended up with memory from another one.
+ but ended up with memory from another node.
-local_node A process ran on this node and got memory from it.
+local_node A process ran on this node's CPU,
+ and got memory from this node.
-other_node A process ran on this node and got memory from another node.
+other_node A process ran on a different node's CPU
+ and got memory from this node.
interleave_hit Interleaving wanted to allocate from this node
and succeeded.
@@ -28,3 +45,11 @@ For easier reading you can use the numastat utility from the numactl package
(http://oss.sgi.com/projects/libnuma/). Note that it only works
well right now on machines with a small number of CPUs.
+Note that on systems with memoryless nodes (where a node has CPUs but no
+memory) the numa_hit, numa_miss and numa_foreign statistics can be skewed
+heavily. In the current kernel implementation, if a process prefers a
+memoryless node (i.e. because it is running on one of its local CPU), the
+implementation actually treats one of the nearest nodes with memory as the
+preferred node. As a result, such allocation will not increase the numa_foreign
+counter on the memoryless node, and will skew the numa_hit, numa_miss and
+numa_foreign statistics of the nearest node.