[RFC PATCH 0/5] mm/damon/sysfs: add a file for efficiently get total size of DAMOS tried regions

[RFC PATCH 0/5] mm/damon/sysfs: add a file for efficiently get total size of DAMOS tried regions

[SeongJae Park]

The tried_regions directory of DAMON sysfs interface is useful for
retrieving monitoring results snapshot or DAMOS debugging.  However, for
common use case that need to monitor only the total size of the scheme
tried regions (e.g., monitoring working set size), the kernel overhead
for directory construction and user overhead for reading the content
could be high if the number of monitoring region is not small.  This
patchset implements DAMON sysfs files for efficient support of the use
case.

The first patch implements the sysfs file to reduce the user space
overhead, and the second patch implements a command for reducing the
kernel space overhead.

The third patch adds a selftest for the new file, and following two
patches update documents.

SeongJae Park (5):
  mm/damon/sysfs-schemes: implement DAMOS tried total bytes file
  mm/damon/sysfs: implement a command for updating only schemes tried
    total bytes
  selftests/damon/sysfs: test tried_regions/total_bytes file
  Docs/ABI/damon: update for tried_regions/total_bytes
  Docs/admin-guide/mm/damon/usage: update for tried_regions/total_bytes

 .../ABI/testing/sysfs-kernel-mm-damon         | 13 +++++-
 Documentation/admin-guide/mm/damon/usage.rst  | 42 ++++++++++++-------
 mm/damon/sysfs-common.h                       |  2 +-
 mm/damon/sysfs-schemes.c                      | 24 ++++++++++-
 mm/damon/sysfs.c                              | 26 +++++++++---
 tools/testing/selftests/damon/sysfs.sh        |  1 +
 6 files changed, 83 insertions(+), 25 deletions(-)

-- 
2.25.1

[RFC PATCH 4/5] Docs/ABI/damon: update for tried_regions/total_bytes

[SeongJae Park]

Update the DAMON ABI document for newly added
schemes/.../tried_regions/total_bytes file and the
update_schemes_tried_bytes command.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/ABI/testing/sysfs-kernel-mm-damon | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-damon b/Documentation/ABI/testing/sysfs-kernel-mm-damon
index 2744f21b5a6b..3d9aaa1cafa9 100644
--- a/Documentation/ABI/testing/sysfs-kernel-mm-damon
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-damon
@@ -29,8 +29,10 @@ Description:	Writing 'on' or 'off' to this file makes the kdamond starts or
 		file updates contents of schemes stats files of the kdamond.
 		Writing 'update_schemes_tried_regions' to the file updates
 		contents of 'tried_regions' directory of every scheme directory
-		of this kdamond.  Writing 'clear_schemes_tried_regions' to the
-		file removes contents of the 'tried_regions' directory.
+		of this kdamond.  Writing 'update_schemes_tried_bytes' to the
+		file updates only '.../tried_regions/total_bytes' files of this
+		kdamond.  Writing 'clear_schemes_tried_regions' to the file
+		removes contents of the 'tried_regions' directory.
 
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/pid
 Date:		Mar 2022
@@ -317,6 +319,13 @@ Contact:	SeongJae Park <sj@kernel.org>
 Description:	Reading this file returns the number of the exceed events of
 		the scheme's quotas.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/tried_regions/total_bytes
+Date:		Jul 2023
+Contact:	SeongJae Park <sj@kernel.org>
+Description:	Reading this file returns the total amount of memory that
+		corresponding DAMON-based Operation Scheme's action has tried
+		to be applied.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/tried_regions/<R>/start
 Date:		Oct 2022
 Contact:	SeongJae Park <sj@kernel.org>
-- 
2.25.1

[RFC PATCH 5/5] Docs/admin-guide/mm/damon/usage: update for tried_regions/total_bytes

[SeongJae Park]

Update the DAMON usage document for newly added
schemes/.../tried_regions/total_bytes file and the
update_schemes_tried_bytes command.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/usage.rst | 42 +++++++++++++-------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 2d495fa85a0e..1859dd6c3834 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -87,7 +87,7 @@ comma (","). ::
     │ │ │ │ │ │ │ filters/nr_filters
     │ │ │ │ │ │ │ │ 0/type,matching,memcg_id
     │ │ │ │ │ │ │ stats/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds
-    │ │ │ │ │ │ │ tried_regions/
+    │ │ │ │ │ │ │ tried_regions/total_bytes
     │ │ │ │ │ │ │ │ 0/start,end,nr_accesses,age
     │ │ │ │ │ │ │ │ ...
     │ │ │ │ │ │ ...
@@ -127,14 +127,18 @@ in the state.  Writing ``commit`` to the ``state`` file makes kdamond reads the
 user inputs in the sysfs files except ``state`` file again.  Writing
 ``update_schemes_stats`` to ``state`` file updates the contents of stats files
 for each DAMON-based operation scheme of the kdamond.  For details of the
-stats, please refer to :ref:`stats section <sysfs_schemes_stats>`.  Writing
-``update_schemes_tried_regions`` to ``state`` file updates the DAMON-based
-operation scheme action tried regions directory for each DAMON-based operation
-scheme of the kdamond.  Writing ``clear_schemes_tried_regions`` to ``state``
-file clears the DAMON-based operating scheme action tried regions directory for
-each DAMON-based operation scheme of the kdamond.  For details of the
-DAMON-based operation scheme action tried regions directory, please refer to
-:ref:`tried_regions section <sysfs_schemes_tried_regions>`.
+stats, please refer to :ref:`stats section <sysfs_schemes_stats>`.
+
+Writing ``update_schemes_tried_regions`` to ``state`` file updates the
+DAMON-based operation scheme action tried regions directory for each
+DAMON-based operation scheme of the kdamond.  Writing
+``update_schemes_tried_bytes`` to ``state`` file updates only
+``.../tried_regions/total_bytes`` files.  Writing
+``clear_schemes_tried_regions`` to ``state`` file clears the DAMON-based
+operating scheme action tried regions directory for each DAMON-based operation
+scheme of the kdamond.  For details of the DAMON-based operation scheme action
+tried regions directory, please refer to :ref:`tried_regions section
+<sysfs_schemes_tried_regions>`.
 
 If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread.
 
@@ -406,13 +410,21 @@ stats by writing a special keyword, ``update_schemes_stats`` to the relevant
 schemes/<N>/tried_regions/
 --------------------------
 
+This directory initially has one file, ``total_bytes``.
+
 When a special keyword, ``update_schemes_tried_regions``, is written to the
-relevant ``kdamonds/<N>/state`` file, DAMON creates directories named integer
-starting from ``0`` under this directory.  Each directory contains files
-exposing detailed information about each of the memory region that the
-corresponding scheme's ``action`` has tried to be applied under this directory,
-during next :ref:`aggregation interval <sysfs_monitoring_attrs>`.  The
-information includes address range, ``nr_accesses``, and ``age`` of the region.
+relevant ``kdamonds/<N>/state`` file, DAMON updates the ``total_bytes`` file so
+that reading it returns the total size of the scheme tried regions, and creates
+directories named integer starting from ``0`` under this directory.  Each
+directory contains files exposing detailed information about each of the memory
+region that the corresponding scheme's ``action`` has tried to be applied under
+this directory, during next :ref:`aggregation interval
+<sysfs_monitoring_attrs>`.  The information includes address range,
+``nr_accesses``, and ``age`` of the region.
+
+Writing ``update_schemes_tried_bytes`` to the relevant ``kdamonds/<N>/state``
+file will only update the ``total_bytes`` file, and will not create the
+subdirectories.
 
 The directories will be removed when another special keyword,
 ``clear_schemes_tried_regions``, is written to the relevant
-- 
2.25.1