[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 1/5] mm/damon/sysfs-schemes: implement DAMOS tried total bytes file

[SeongJae Park]

The tried_regions directory can be used for retrieving the monitoring
results snapshot for regions of specific access pattern, by setting the
scheme's action as 'stat' and the access pattern as required.  While the
interface provides every detail of the monitoring results, some use
cases including working set size monitoring requires only the total size
of the regions.  For such cases, users should read all the information
and calculate the total size of the regions.  However, it could incur
high overhead if the number of regions is high.  Add a file for
retrieving only the information, namely 'total_bytes' file.  It allows
users to get the total size by reading only the file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 50cf89dcd898..6d3462eb31f2 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -117,6 +117,7 @@ struct damon_sysfs_scheme_regions {
 	struct kobject kobj;
 	struct list_head regions_list;
 	int nr_regions;
+	unsigned long total_bytes;
 };
 
 static struct damon_sysfs_scheme_regions *
@@ -128,9 +129,19 @@ damon_sysfs_scheme_regions_alloc(void)
 	regions->kobj = (struct kobject){};
 	INIT_LIST_HEAD(&regions->regions_list);
 	regions->nr_regions = 0;
+	regions->total_bytes = 0;
 	return regions;
 }
 
+static ssize_t total_bytes_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_scheme_regions *regions = container_of(kobj,
+			struct damon_sysfs_scheme_regions, kobj);
+
+	return sysfs_emit(buf, "%lu\n", regions->total_bytes);
+}
+
 static void damon_sysfs_scheme_regions_rm_dirs(
 		struct damon_sysfs_scheme_regions *regions)
 {
@@ -148,7 +159,11 @@ static void damon_sysfs_scheme_regions_release(struct kobject *kobj)
 	kfree(container_of(kobj, struct damon_sysfs_scheme_regions, kobj));
 }
 
+static struct kobj_attribute damon_sysfs_scheme_regions_total_bytes_attr =
+		__ATTR_RO_MODE(total_bytes, 0400);
+
 static struct attribute *damon_sysfs_scheme_regions_attrs[] = {
+	&damon_sysfs_scheme_regions_total_bytes_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_scheme_regions);
@@ -1648,6 +1663,7 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 		return 0;
 
 	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
+	sysfs_regions->total_bytes += r->ar.end - r->ar.start;
 	region = damon_sysfs_scheme_region_alloc(r);
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
 	sysfs_regions->nr_regions++;
@@ -1678,6 +1694,7 @@ int damon_sysfs_schemes_clear_regions(
 		sysfs_scheme = sysfs_schemes->schemes_arr[schemes_idx++];
 		damon_sysfs_scheme_regions_rm_dirs(
 				sysfs_scheme->tried_regions);
+		sysfs_scheme->tried_regions->total_bytes = 0;
 	}
 	return 0;
 }
-- 
2.25.1

[RFC PATCH 2/5] mm/damon/sysfs: implement a command for updating only schemes tried total bytes

[SeongJae Park]

Using tried_regions/total_bytes file, users can efficiently retrieve the
total size of memory regions having specific access pattern.  However,
DAMON sysfs interface in kernel still populates all the infomration on
the tried_regions subdirectories.  That means the kernel part overhead
for the construction of tried regions directories still exists.  To
remove the overhead, implement yet another command input for 'state'
DAMON sysfs file.  Writing the input to the file makes DAMON sysfs
interface to update only the total_bytes file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-common.h  |  2 +-
 mm/damon/sysfs-schemes.c |  7 ++++++-
 mm/damon/sysfs.c         | 26 ++++++++++++++++++++------
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/mm/damon/sysfs-common.h b/mm/damon/sysfs-common.h
index db677eba78fd..fd482a0639b4 100644
--- a/mm/damon/sysfs-common.h
+++ b/mm/damon/sysfs-common.h
@@ -47,7 +47,7 @@ void damon_sysfs_schemes_update_stats(
 
 int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx);
+		struct damon_ctx *ctx, bool total_bytes_only);
 
 int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
 
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 6d3462eb31f2..9a015079f3a4 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1635,6 +1635,7 @@ void damon_sysfs_schemes_update_stats(
  */
 static struct damon_sysfs_schemes *damon_sysfs_schemes_for_damos_callback;
 static int damon_sysfs_schemes_region_idx;
+static bool damos_regions_upd_total_bytes_only;
 
 /*
  * DAMON callback that called before damos apply.  While this callback is
@@ -1664,6 +1665,9 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 
 	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
 	sysfs_regions->total_bytes += r->ar.end - r->ar.start;
+	if (damos_regions_upd_total_bytes_only)
+		return 0;
+
 	region = damon_sysfs_scheme_region_alloc(r);
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
 	sysfs_regions->nr_regions++;
@@ -1702,10 +1706,11 @@ int damon_sysfs_schemes_clear_regions(
 /* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
 int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx)
+		struct damon_ctx *ctx, bool total_bytes_only)
 {
 	damon_sysfs_schemes_clear_regions(sysfs_schemes, ctx);
 	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
+	damos_regions_upd_total_bytes_only = total_bytes_only;
 	ctx->callback.before_damos_apply = damon_sysfs_before_damos_apply;
 	return 0;
 }
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 533d06052c09..808a8efe0523 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -999,6 +999,11 @@ enum damon_sysfs_cmd {
 	 * files.
 	 */
 	DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS,
+	/*
+	 * @DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES: Update
+	 * tried_regions/total_bytes sysfs files for each scheme.
+	 */
+	DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES,
 	/*
 	 * @DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS: Update schemes tried
 	 * regions
@@ -1021,6 +1026,7 @@ static const char * const damon_sysfs_cmd_strs[] = {
 	"off",
 	"commit",
 	"update_schemes_stats",
+	"update_schemes_tried_bytes",
 	"update_schemes_tried_regions",
 	"clear_schemes_tried_regions",
 };
@@ -1206,12 +1212,14 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 {
 	struct damon_target *t, *next;
 	struct damon_sysfs_kdamond *kdamond;
+	enum damon_sysfs_cmd cmd;
 
 	/* damon_sysfs_schemes_update_regions_stop() might not yet called */
 	kdamond = damon_sysfs_cmd_request.kdamond;
-	if (kdamond && damon_sysfs_cmd_request.cmd ==
-			DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS &&
-			ctx == kdamond->damon_ctx) {
+	cmd = damon_sysfs_cmd_request.cmd;
+	if (kdamond && ctx == kdamond->damon_ctx &&
+			(cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS ||
+			 cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES)) {
 		damon_sysfs_schemes_update_regions_stop(ctx);
 		mutex_unlock(&damon_sysfs_lock);
 	}
@@ -1248,14 +1256,15 @@ static int damon_sysfs_upd_schemes_stats(struct damon_sysfs_kdamond *kdamond)
 }
 
 static int damon_sysfs_upd_schemes_regions_start(
-		struct damon_sysfs_kdamond *kdamond)
+		struct damon_sysfs_kdamond *kdamond, bool total_bytes_only)
 {
 	struct damon_ctx *ctx = kdamond->damon_ctx;
 
 	if (!ctx)
 		return -EINVAL;
 	return damon_sysfs_schemes_update_regions_start(
-			kdamond->contexts->contexts_arr[0]->schemes, ctx);
+			kdamond->contexts->contexts_arr[0]->schemes, ctx,
+			total_bytes_only);
 }
 
 static int damon_sysfs_upd_schemes_regions_stop(
@@ -1332,6 +1341,7 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 {
 	struct damon_sysfs_kdamond *kdamond;
 	static bool damon_sysfs_schemes_regions_updating;
+	bool total_bytes_only = false;
 	int err = 0;
 
 	/* avoid deadlock due to concurrent state_store('off') */
@@ -1348,9 +1358,13 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 	case DAMON_SYSFS_CMD_COMMIT:
 		err = damon_sysfs_commit_input(kdamond);
 		break;
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES:
+		total_bytes_only = true;
+		fallthrough;
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS:
 		if (!damon_sysfs_schemes_regions_updating) {
-			err = damon_sysfs_upd_schemes_regions_start(kdamond);
+			err = damon_sysfs_upd_schemes_regions_start(kdamond,
+					total_bytes_only);
 			if (!err) {
 				damon_sysfs_schemes_regions_updating = true;
 				goto keep_lock_out;
-- 
2.25.1

[RFC PATCH 3/5] selftests/damon/sysfs: test tried_regions/total_bytes file

[SeongJae Park]

Update sysfs.sh DAMON selftest for checking existence of 'total_bytes'
file under the 'tried_regions' directory of DAMON sysfs interface.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/sysfs.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/damon/sysfs.sh b/tools/testing/selftests/damon/sysfs.sh
index bcd4734ca094..967e27267549 100644
--- a/tools/testing/selftests/damon/sysfs.sh
+++ b/tools/testing/selftests/damon/sysfs.sh
@@ -84,6 +84,7 @@ test_tried_regions()
 {
 	tried_regions_dir=$1
 	ensure_dir "$tried_regions_dir" "exist"
+	ensure_file "$tried_regions_dir/total_bytes" "exist" "400"
 }
 
 test_stats()
-- 
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