DAOS-14411 dfuse: Add daos fs query

docs/user/filesystem.md

@@ -696,6 +696,30 @@ These are two command line options to control the DFuse process itself.
 
 These will affect all containers accessed via DFuse, regardless of any container attributes.
 
+### Managing memory usage and disconnecting from containers
+
+DFuse can be instructed to evict paths from local memory which drops any open handles on containers
+or pools as well as reducing the working set size and memory consumption.  This is an asynchronous
+operation and there is no automatic way to tell if it's completed.  In addition, any lookup of the
+path specified in the eviction call will cause a new lookup and prevent the eviction from
+completing.
+
+Paths can be requested for eviction from dfuse using the `daos filesystem evict` command.  This does
+not change any data that is stored in DAOS in any way but rather releases local resources.  This
+command will return the inode number of the path as well as key dfuse metrics.
+
+DFuse metrics can be queried with the `daos filesystem query` command which takes an optional
+`--inode` parameter.  This will return information on the number of inodes held in memory, the
+number of open files as well as the number of pools and containers that DFuse is connected to.  If
+the `--inode` option is given then this command will also report if the inode is in memory or not.
+
+Together these two commands can be used to request eviction of a path and to poll for its release,
+although lookups from other processes might block the eviction process.
+
+If `daos filesystem evict` is passed the root of the DFuse mount then the path itself cannot be
+evicted - in this case all top-level entries in the directory are evicted instead and no inode
+number is returned.
+
 ### Permissions
 
 DFuse can serve data from any user's container, but needs appropriate permissions in order to do