doc: update documentation

Fixes: https://tracker.ceph.com/issues/68931
Signed-off-by: Igor Golikov <[email protected]>

Author: salieri11

doc/cephfs/mds-config-ref.rst

@@ -1,3 +1,4 @@
+.. _MDS Config Reference:
 ======================
  MDS Config Reference
 ======================
@@ -65,3 +66,4 @@
 .. confval:: mds_min_caps_per_client
 .. confval:: mds_symlink_recovery
 .. confval:: mds_extraordinary_events_dump_interval
+.. confval:: subv_metrics_window_interval

doc/cephfs/metrics.rst

@@ -66,6 +66,40 @@ CephFS exports client metrics as :ref:`Labeled Perf Counters`, which could be us
      - Gauge
      - Number of bytes written in input/output operations generated by all processes
 
+Subvolume Metrics
+-----------------
+
+CephFS exports subvolume metrics as :ref:`Labeled Perf Counters`, which could be used to monitor the subvolume performance. CephFS exports the below subvolume metrics.
+Subvolume metrics are aggregated within sliding window of 30 seconds (default value, configurable via the ``subv_metrics_window_interval`` parameter, see :ref:`MDS config reference`).
+In large Ceph clusters with tens of thousands of subvolumes, this parameter also helps clean up stale metrics.
+When a subvolume’s sliding window becomes empty, it's metrics are removed and not reported as “zero” values, reducing memory usage and computational overhead.
+
+.. list-table:: Subvolume Metrics
+   :widths: 25 25 75
+   :header-rows: 1
+
+   * - Name
+     - Type
+     - Description
+   * - ``avg_read_iops``
+     - Gauge
+     - Average read IOPS (input/output operations per second) over the sliding window.
+   * - ``avg_read_tp_Bps``
+     - Gauge
+     - Average read throughput in bytes per second.
+   * - ``avg_read_lat_msec``
+     - Gauge
+     - Average read latency in milliseconds.
+   * - ``avg_write_iops``
+     - Gauge
+     - Average write IOPS over the sliding window.
+   * - ``avg_write_tp_Bps``
+     - Gauge
+     - Average write throughput in bytes per second.
+   * - ``avg_write_lat_msec``
+     - Gauge
+     - Average write latency in milliseconds.
+
 Getting Metrics
 ===============
 
@@ -130,3 +164,21 @@ The metrics could be scraped from the MDS admin socket as well as using the tell
             }
         }
     ]
+
+The subvolume metrics are dumped as a part of the same command. The ``mds_subvolume_metrics`` section in the output of ``counter dump`` command displays the metrics for each client as shown below::
+
+    "mds_subvolume_metrics": [
+        {
+            "labels": {
+                "fs_name": "a",
+                "subvolume_path": "/volumes/_nogroup/test_subvolume"
+            },
+            "counters": {
+                "avg_read_iops": 0,
+                "avg_read_tp_Bps": 11,
+                "avg_read_lat_msec": 0,
+                "avg_write_iops": 1564,
+                "avg_write_tp_Bps": 6408316,
+                "avg_write_lat_msec": 338
+            }
+        }

src/common/options/mds.yaml.in

@@ -1807,8 +1807,8 @@ options:
   type: secs
   level: dev
   desc: subvolume metrics sliding window interval, seconds
-  long_desc: interval in seconds to hold values in sliding window for subvolume metrics, in the metrics aggregator
-  default: 60
+  long_desc: interval in seconds to hold values in sliding window for subvolume metrics
+  default: 30
   min: 30
   services:
   - mds