Docs/{ABI,admin-guide}/damon: document 'avail_operations' sysfs file

This commit updates the DAMON ABI and usage documents for the new sysfs
file, 'avail_operations'.

Link: https://lkml.kernel.org/r/20220426203843.45238-5-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/ABI/testing/sysfs-kernel-mm-damon

@@ -40,6 +40,12 @@ Description:	Writing a number 'N' to this file creates the number of
 		directories for controlling each DAMON context named '0' to
 		'N-1' under the contexts/ directory.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/avail_operations
+Date:		Apr 2022
+Contact:	SeongJae Park <sj@kernel.org>
+Description:	Reading this file returns the available monitoring operations
+		sets on the currently running kernel.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/operations
 Date:		Mar 2022
 Contact:	SeongJae Park <sj@kernel.org>
@@ -47,7 +53,9 @@ Description:	Writing a keyword for a monitoring operations set ('vaddr' for
 		virtual address spaces monitoring, and 'paddr' for the physical
 		address space monitoring) to this file makes the context to use
 		the operations set.  Reading the file returns the keyword for
-		the operations set the context is set to use.
+		the operations set the context is set to use.  Note that only
+		the operations sets that listed in 'avail_operations' file are
+		valid inputs.
 
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/monitoring_attrs/intervals/sample_us
 Date:		Mar 2022

Documentation/admin-guide/mm/damon/usage.rst

@@ -68,7 +68,7 @@ comma (","). ::
     │ kdamonds/nr_kdamonds
     │ │ 0/state,pid
     │ │ │ contexts/nr_contexts
-    │ │ │ │ 0/operations
+    │ │ │ │ 0/avail_operations,operations
     │ │ │ │ │ monitoring_attrs/
     │ │ │ │ │ │ intervals/sample_us,aggr_us,update_us
     │ │ │ │ │ │ nr_regions/min,max
@@ -143,17 +143,23 @@ be written to the file.
 contexts/<N>/
 -------------
 
-In each context directory, one file (``operations``) and three directories
-(``monitoring_attrs``, ``targets``, and ``schemes``) exist.
+In each context directory, two files (``avail_operations`` and ``operations``)
+and three directories (``monitoring_attrs``, ``targets``, and ``schemes``)
+exist.
 
 DAMON supports multiple types of monitoring operations, including those for
-virtual address space and the physical address space.  You can set and get what
-type of monitoring operations DAMON will use for the context by writing one of
-below keywords to, and reading from the file.
+virtual address space and the physical address space.  You can get the list of
+available monitoring operations set on the currently running kernel by reading
+``avail_operations`` file.  Based on the kernel configuration, the file will
+list some or all of below keywords.
 
  - vaddr: Monitor virtual address spaces of specific processes
  - paddr: Monitor the physical address space of the system
 
+You can set and get what type of monitoring operations DAMON will use for the
+context by writing one of the keywords listed in ``avail_operations`` file and
+reading from the ``operations`` file.
+
 contexts/<N>/monitoring_attrs/
 ------------------------------