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Diffstat (limited to 'Documentation/admin-guide/numastat.rst')
| -rw-r--r-- | Documentation/admin-guide/numastat.rst | 31 |
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. |