[RFC PATCH 0/9] mm/damon: replace most damon_callback usages in sysfs with new core functions

[RFC PATCH 0/9] mm/damon: replace most damon_callback usages in sysfs with new core functions

[SeongJae Park]

DAMON provides damon_callback API that notifies monitoring events and
allows safe access to damon_ctx internal data.  Users can set and unset
callback functions for different monitoring events in damon_ctx.  Then
DAMON worker thread (kdamond) calls back the functions on the events as
long as the function is set on the damon_ctx.

It is designed in such simple way because it was sufficient for usages
of DAMON at the early days.  We also wanted to make it flexible so that
API client code can implement any required additional features on top of
damon_callback on their demands.

As expected, more sophisticated usages have invented.  Online updates
of parameters or DAMOS auto-tuning inputs and retrieval of DAMOS
statistics and tried regions are notable such usages.  Because
damon_callback doesn't provide any explict synchronization mechanism,
the user ABIs for exposing such functionalities are implemented in
asynchronous ways (DAMON_RECLAIM and DAMON_LRU_SORT}), or synchronous
ways (DAMON_SYSFS) with additional synchronization mechanisms that built
inside the ABI implementation, on top of damon_callback.

So damon_callback is working as expected.  However, the additional
mechanisms built inside ABI on top of damon_callback beocming somewhat
too big and not easy to maintain.  damon_callback is basically simple
enougy to use in not only correct but also wrong ways.  The additional
mechanisms can be easier to maintain when implemented inside core logic.

Introduce two new DAMON core API, namely 'damon_call()' and
'damos_walk()'.  The two functions support synchronous access to
- damon_ctx internal data including DAMON parameters and monitoring
  results, and
- DAMOS-specific data such as regions that each DAMOS action is applied,
respectively.

And replace most of damon_callback usages from DAMON sysfs with the new
core API functions.  Online DAMON parameters tuning feature is not
replaced in this series, since it has specific callback timing
assumptions that require more works.

Patch sequence
==============

First two patches removes unnecessary synchronization dependency of
clear_schemes_tried_regions command handling.

Third patch implements one of the new DAMON API, damon_call().  Three
patches replacing damon_callback usages in DAMON sysfs interface using
damon_call() follow.

Then, seventh patch introduces the other new DAMON API, damos_walk().
Eighth patch replaces two damon_callback usages in DAMON sysfs interface
using damos_walk().  The ninth patch finally cleans up code that no more
being used.

SeongJae Park (9):
  mm/damon/sysfs-schemes: remove unnecessary schemes existence check in
    damon_sysfs_schemes_clear_regions()
  mm/damon/sysfs: handle clear_schemes_tried_regions from DAMON sysfs
    context
  mm/damon/core: implement damon_call()
  mm/damon/sysfs: use damon_call() for update_schemes_stats
  mm/damon/sysfs: use damon_call() for commit_schemes_quota_goals
  mm/damon/sysfs: use damon_call() for update_schemes_effective_quotas
  mm/damon/core: implement damos_walk()
  mm/damon/sysfs: use damos_walk() for
    update_schemes_tried_{bytes,regions}
  mm/damon/sysfs: remove unused code for schemes tried regions update

 include/linux/damon.h    |  59 ++++++++++-
 mm/damon/core.c          | 220 +++++++++++++++++++++++++++++++++++++++
 mm/damon/sysfs-common.h  |  16 +--
 mm/damon/sysfs-schemes.c | 206 ++++--------------------------------
 mm/damon/sysfs.c         | 187 +++++++++++++++------------------
 5 files changed, 386 insertions(+), 302 deletions(-)


base-commit: e5c48d400cab89a0539ce822ba805f0ad4209e87
-- 
2.39.5

[RFC PATCH 1/9] mm/damon/sysfs-schemes: remove unnecessary schemes existence check in damon_sysfs_schemes_clear_regions()

[SeongJae Park]

damon_sysfs_schemes_clear_regions() skips removing the scheme tried
region directories only if the matching scheme is still ongoing.  It is
unnecessary check, since what users want is just removing the entire
region directories.  Remove the unnecessary check.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-common.h  |  3 +--
 mm/damon/sysfs-schemes.c | 16 +++++-----------
 mm/damon/sysfs.c         |  2 +-
 3 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/mm/damon/sysfs-common.h b/mm/damon/sysfs-common.h
index 9a18f3c535d3..e79b4a65ff2d 100644
--- a/mm/damon/sysfs-common.h
+++ b/mm/damon/sysfs-common.h
@@ -56,8 +56,7 @@ bool damos_sysfs_regions_upd_done(void);
 int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
 
 int damon_sysfs_schemes_clear_regions(
-		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx);
+		struct damon_sysfs_schemes *sysfs_schemes);
 
 int damos_sysfs_set_quota_scores(struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx);
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 25356fe99273..65f6d3339a77 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2213,20 +2213,14 @@ void damos_sysfs_mark_finished_regions_updates(struct damon_ctx *ctx)
 
 /* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
 int damon_sysfs_schemes_clear_regions(
-		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx)
+		struct damon_sysfs_schemes *sysfs_schemes)
 {
-	struct damos *scheme;
-	int schemes_idx = 0;
+	int i;
 
-	damon_for_each_scheme(scheme, ctx) {
+	for (i = 0; i < sysfs_schemes->nr; i++) {
 		struct damon_sysfs_scheme *sysfs_scheme;
 
-		/* user could have removed the scheme sysfs dir */
-		if (schemes_idx >= sysfs_schemes->nr)
-			break;
-
-		sysfs_scheme = sysfs_schemes->schemes_arr[schemes_idx++];
+		sysfs_scheme = sysfs_schemes->schemes_arr[i];
 		damon_sysfs_scheme_regions_rm_dirs(
 				sysfs_scheme->tried_regions);
 		sysfs_scheme->tried_regions->total_bytes = 0;
@@ -2276,7 +2270,7 @@ int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx, bool total_bytes_only)
 {
-	damon_sysfs_schemes_clear_regions(sysfs_schemes, ctx);
+	damon_sysfs_schemes_clear_regions(sysfs_schemes);
 	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
 	damos_tried_regions_init_upd_status(sysfs_schemes, ctx);
 	damos_regions_upd_total_bytes_only = total_bytes_only;
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 4daac92be30b..71bc2622ab35 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1262,7 +1262,7 @@ static int damon_sysfs_clear_schemes_regions(
 	if (!ctx)
 		return -EINVAL;
 	return damon_sysfs_schemes_clear_regions(
-			kdamond->contexts->contexts_arr[0]->schemes, ctx);
+			kdamond->contexts->contexts_arr[0]->schemes);
 }
 
 static inline bool damon_sysfs_kdamond_running(
-- 
2.39.5

[RFC PATCH 2/9] mm/damon/sysfs: handle clear_schemes_tried_regions from DAMON sysfs context

[SeongJae Park]

DAMON sysfs interface handles clear_schemes_tried_regions from DAMON
callback context (damon_sysfs_cmd_request_callback()).  But no DAMON
internal data is accessed for the work.  Directly handle it from DAMON
sysfs interface context, namely damon_sysfs_handle_cmd().

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c |  2 +-
 mm/damon/sysfs.c         | 17 +++--------------
 2 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 65f6d3339a77..6c8f9eae75af 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2265,7 +2265,7 @@ static void damos_tried_regions_init_upd_status(
 	}
 }
 
-/* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
+/* Called while damon_sysfs_lock is hold */
 int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx, bool total_bytes_only)
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 71bc2622ab35..8cb940d21fbe 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1254,17 +1254,6 @@ static int damon_sysfs_upd_schemes_regions_stop(
 	return damon_sysfs_schemes_update_regions_stop(ctx);
 }
 
-static int damon_sysfs_clear_schemes_regions(
-		struct damon_sysfs_kdamond *kdamond)
-{
-	struct damon_ctx *ctx = kdamond->damon_ctx;
-
-	if (!ctx)
-		return -EINVAL;
-	return damon_sysfs_schemes_clear_regions(
-			kdamond->contexts->contexts_arr[0]->schemes);
-}
-
 static inline bool damon_sysfs_kdamond_running(
 		struct damon_sysfs_kdamond *kdamond)
 {
@@ -1417,9 +1406,6 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 			damon_sysfs_schemes_regions_updating = false;
 		}
 		break;
-	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
-		err = damon_sysfs_clear_schemes_regions(kdamond);
-		break;
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_EFFECTIVE_QUOTAS:
 		err = damon_sysfs_upd_schemes_effective_quotas(kdamond);
 		break;
@@ -1549,6 +1535,9 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 		return damon_sysfs_turn_damon_on(kdamond);
 	case DAMON_SYSFS_CMD_OFF:
 		return damon_sysfs_turn_damon_off(kdamond);
+	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
+		return damon_sysfs_schemes_clear_regions(
+			kdamond->contexts->contexts_arr[0]->schemes);
 	default:
 		break;
 	}
-- 
2.39.5

[RFC PATCH 3/9] mm/damon/core: implement damon_call()

[SeongJae Park]

Introduce a new DAMON core API function, damon_call().  It aims to
replace some damon_callback usages that access damon_ctx of ongoing
kdamond with additional synchronizations.  It receives a function
pointer, let the parallel kdamond invokes the function, and returns
after the invocation is finished, or canceled due to some races.

kdamond invokes the function inside the main loop after sampling is
done.  If it is deactivated by DAMOS watermarks or already out of the
main loop, mark the request as canceled so that damon_call() can wakeup
and return.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 26 +++++++++++++
 mm/damon/core.c       | 86 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 112 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 10fc6df52111..529ea578f2d5 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -590,6 +590,27 @@ struct damon_callback {
 	void (*before_terminate)(struct damon_ctx *context);
 };
 
+/*
+ * struct damon_call_control - Control damon_call().
+ *
+ * @fn:			Function to be called back.
+ * @data:		Data that will be passed to @fn.
+ * @return_code:	Return code from @fn invocation.
+ *
+ * Control damon_call(), which requests specific kdamond to invoke a given
+ * function.  Refer to damon_call() for more details.
+ */
+struct damon_call_control {
+	int (*fn)(void *data);
+	void *data;
+	int return_code;
+/* private: internal use only */
+	/* informs if the kdamond finished handling of the request */
+	struct completion completion;
+	/* informs if the kdamond canceled @fn infocation */
+	bool canceled;
+};
+
 /**
  * struct damon_attrs - Monitoring attributes for accuracy/overhead control.
  *
@@ -670,6 +691,9 @@ struct damon_ctx {
 	/* for scheme quotas prioritization */
 	unsigned long *regions_score_histogram;
 
+	struct damon_call_control *call_control;
+	struct mutex call_control_lock;
+
 /* public: */
 	struct task_struct *kdamond;
 	struct mutex kdamond_lock;
@@ -817,6 +841,8 @@ static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs
 int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive);
 int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
 
+int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
+
 int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end);
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index bf04987a91c6..89a679c06e30 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -533,6 +533,7 @@ struct damon_ctx *damon_new_ctx(void)
 	ctx->next_ops_update_sis = 0;
 
 	mutex_init(&ctx->kdamond_lock);
+	mutex_init(&ctx->call_control_lock);
 
 	ctx->attrs.min_nr_regions = 10;
 	ctx->attrs.max_nr_regions = 1000;
@@ -1183,6 +1184,54 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs)
 	return err;
 }
 
+static bool damon_is_running(struct damon_ctx *ctx)
+{
+	bool running;
+
+	mutex_lock(&ctx->kdamond_lock);
+	running = ctx->kdamond != NULL;
+	mutex_unlock(&ctx->kdamond_lock);
+	return running;
+}
+
+/**
+ * damon_call() - Invoke a given function on DAMON worker thread (kdamond).
+ * @ctx:	DAMON context to call the function for.
+ * @control:	Control variable of the call request.
+ *
+ * Ask DAMON worker thread (kdamond) of @ctx to call a function with an
+ * argument data that respectively passed via &damon_call_control->fn and
+ * &damon_call_control->data of @control, and wait until the kdamond finishes
+ * handling of the request.
+ *
+ * The kdamond executes the function with the argument in the main loop, just
+ * after a sampling of the iteration is finished.  The function can hence
+ * safely access the internal data of the &struct damon_ctx without additional
+ * synchronization.  The return value of the function will be saved in
+ * &damon_call_control->return_code.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
+{
+	init_completion(&control->completion);
+	control->canceled = false;
+
+	mutex_lock(&ctx->call_control_lock);
+	if (ctx->call_control) {
+		mutex_unlock(&ctx->call_control_lock);
+		return -EBUSY;
+	}
+	ctx->call_control = control;
+	mutex_unlock(&ctx->call_control_lock);
+	if (!damon_is_running(ctx))
+		return -EINVAL;
+	wait_for_completion(&control->completion);
+	if (control->canceled)
+		return -ECANCELED;
+	return 0;
+}
+
 /*
  * Reset the aggregated monitoring results ('nr_accesses' of each region).
  */
@@ -1970,6 +2019,39 @@ static void kdamond_usleep(unsigned long usecs)
 		usleep_range_idle(usecs, usecs + 1);
 }
 
+/*
+ * kdamond_call() - handle damon_call_control.
+ * @ctx:	The &struct damon_ctx of the kdamond.
+ * @cancel:	Whether to cancel the invocation of the function.
+ *
+ * If there is a &struct damon_call_control request that registered via
+ * &damon_call() on @ctx, do or cancel the invocation of the function depending
+ * on @cancel.  @cancel is set when the kdamond is deactivated by DAMOS
+ * watermarks, or the kdamond is already out of the main loop and therefore
+ * will be terminated.
+ */
+static void kdamond_call(struct damon_ctx *ctx, bool cancel)
+{
+	struct damon_call_control *control;
+	int ret = 0;
+
+	mutex_lock(&ctx->call_control_lock);
+	control = ctx->call_control;
+	mutex_unlock(&ctx->call_control_lock);
+	if (!control)
+		return;
+	if (cancel) {
+		control->canceled = true;
+	} else {
+		ret = control->fn(control->data);
+		control->return_code = ret;
+	}
+	complete(&control->completion);
+	mutex_lock(&ctx->call_control_lock);
+	ctx->call_control = NULL;
+	mutex_unlock(&ctx->call_control_lock);
+}
+
 /* Returns negative error code if it's not activated but should return */
 static int kdamond_wait_activation(struct damon_ctx *ctx)
 {
@@ -1994,6 +2076,7 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
 		if (ctx->callback.after_wmarks_check &&
 				ctx->callback.after_wmarks_check(ctx))
 			break;
+		kdamond_call(ctx, true);
 	}
 	return -EBUSY;
 }
@@ -2065,6 +2148,7 @@ static int kdamond_fn(void *data)
 		if (ctx->callback.after_sampling &&
 				ctx->callback.after_sampling(ctx))
 			break;
+		kdamond_call(ctx, false);
 
 		kdamond_usleep(sample_interval);
 		ctx->passed_sample_intervals++;
@@ -2126,6 +2210,8 @@ static int kdamond_fn(void *data)
 	ctx->kdamond = NULL;
 	mutex_unlock(&ctx->kdamond_lock);
 
+	kdamond_call(ctx, true);
+
 	mutex_lock(&damon_lock);
 	nr_running_ctxs--;
 	if (!nr_running_ctxs && running_exclusive_ctxs)
-- 
2.39.5

[RFC PATCH 4/9] mm/damon/sysfs: use damon_call() for update_schemes_stats

[SeongJae Park]

DAMON sysfs interface uses damon_callback with its own synchronization
facility to handle update_schemes_stats kdamond command.  But
damon_call() can support the use case without the additional
synchronizations.  Convert the code to use damon_call() instead.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 8cb940d21fbe..d30d659c794e 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1214,19 +1214,19 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 
 /*
  * damon_sysfs_upd_schemes_stats() - Update schemes stats sysfs files.
- * @kdamond:	The kobject wrapper that associated to the kdamond thread.
+ * @data:	The kobject wrapper that associated to the kdamond thread.
  *
  * This function reads the schemes stats of specific kdamond and update the
  * related values for sysfs files.  This function should be called from DAMON
- * callbacks while holding ``damon_syfs_lock``, to safely access the DAMON
- * contexts-internal data and DAMON sysfs variables.
+ * worker thread,to safely access the DAMON contexts-internal data.  Caller
+ * should also ensure holding ``damon_syfs_lock``, and ->damon_ctx of @data is
+ * not NULL but a valid pointer, to safely access DAMON sysfs variables.
  */
-static int damon_sysfs_upd_schemes_stats(struct damon_sysfs_kdamond *kdamond)
+static int damon_sysfs_upd_schemes_stats(void *data)
 {
+	struct damon_sysfs_kdamond *kdamond = data;
 	struct damon_ctx *ctx = kdamond->damon_ctx;
 
-	if (!ctx)
-		return -EINVAL;
 	damon_sysfs_schemes_update_stats(
 			kdamond->contexts->contexts_arr[0]->schemes, ctx);
 	return 0;
@@ -1371,9 +1371,6 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 	if (!kdamond || kdamond->damon_ctx != c)
 		goto out;
 	switch (damon_sysfs_cmd_request.cmd) {
-	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS:
-		err = damon_sysfs_upd_schemes_stats(kdamond);
-		break;
 	case DAMON_SYSFS_CMD_COMMIT:
 		if (!after_aggregation)
 			goto out;
@@ -1511,6 +1508,18 @@ static int damon_sysfs_turn_damon_off(struct damon_sysfs_kdamond *kdamond)
 	 */
 }
 
+static int damon_sysfs_damon_call(int (*fn)(void *data),
+		struct damon_sysfs_kdamond *kdamond)
+{
+	struct damon_call_control call_control = {};
+
+	if (!kdamond->damon_ctx)
+		return -EINVAL;
+	call_control.fn = fn;
+	call_control.data = kdamond;
+	return damon_call(kdamond->damon_ctx, &call_control);
+}
+
 /*
  * damon_sysfs_handle_cmd() - Handle a command for a specific kdamond.
  * @cmd:	The command to handle.
@@ -1529,12 +1538,14 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 {
 	bool need_wait = true;
 
-	/* Handle commands that doesn't access DAMON context-internal data */
 	switch (cmd) {
 	case DAMON_SYSFS_CMD_ON:
 		return damon_sysfs_turn_damon_on(kdamond);
 	case DAMON_SYSFS_CMD_OFF:
 		return damon_sysfs_turn_damon_off(kdamond);
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS:
+		return damon_sysfs_damon_call(
+				damon_sysfs_upd_schemes_stats, kdamond);
 	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
 		return damon_sysfs_schemes_clear_regions(
 			kdamond->contexts->contexts_arr[0]->schemes);
-- 
2.39.5

[RFC PATCH 5/9] mm/damon/sysfs: use damon_call() for commit_schemes_quota_goals

[SeongJae Park]

DAMON sysfs interface uses damon_callback with its own synchronization
facility to handle commit_schemes_quota_goals command.  But damon_call()
can support the use case without the additional synchronizations.
Convert the code to use damon_call() instead.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index d30d659c794e..24070f36fa7c 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1307,9 +1307,9 @@ static int damon_sysfs_commit_input(struct damon_sysfs_kdamond *kdamond)
 	return err;
 }
 
-static int damon_sysfs_commit_schemes_quota_goals(
-		struct damon_sysfs_kdamond *sysfs_kdamond)
+static int damon_sysfs_commit_schemes_quota_goals(void *data)
 {
+	struct damon_sysfs_kdamond *sysfs_kdamond = data;
 	struct damon_ctx *ctx;
 	struct damon_sysfs_context *sysfs_ctx;
 
@@ -1376,9 +1376,6 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 			goto out;
 		err = damon_sysfs_commit_input(kdamond);
 		break;
-	case DAMON_SYSFS_CMD_COMMIT_SCHEMES_QUOTA_GOALS:
-		err = damon_sysfs_commit_schemes_quota_goals(kdamond);
-		break;
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES:
 		total_bytes_only = true;
 		fallthrough;
@@ -1543,6 +1540,10 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 		return damon_sysfs_turn_damon_on(kdamond);
 	case DAMON_SYSFS_CMD_OFF:
 		return damon_sysfs_turn_damon_off(kdamond);
+	case DAMON_SYSFS_CMD_COMMIT_SCHEMES_QUOTA_GOALS:
+		return damon_sysfs_damon_call(
+				damon_sysfs_commit_schemes_quota_goals,
+				kdamond);
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS:
 		return damon_sysfs_damon_call(
 				damon_sysfs_upd_schemes_stats, kdamond);
-- 
2.39.5

[RFC PATCH 6/9] mm/damon/sysfs: use damon_call() for update_schemes_effective_quotas

[SeongJae Park]

DAMON sysfs interface uses damon_callback with its own synchronization
facility to handle update_schemes_effective_quotas command.  But
damon_call() can support the use case without the additional
synchronizations.  Convert the code to use damon_call() instead.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 24070f36fa7c..978de4305f2b 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1327,20 +1327,18 @@ static int damon_sysfs_commit_schemes_quota_goals(void *data)
 /*
  * damon_sysfs_upd_schemes_effective_quotas() - Update schemes effective quotas
  * sysfs files.
- * @kdamond:	The kobject wrapper that associated to the kdamond thread.
+ * @data:	The kobject wrapper that associated to the kdamond thread.
  *
  * This function reads the schemes' effective quotas of specific kdamond and
  * update the related values for sysfs files.  This function should be called
  * from DAMON callbacks while holding ``damon_syfs_lock``, to safely access the
  * DAMON contexts-internal data and DAMON sysfs variables.
  */
-static int damon_sysfs_upd_schemes_effective_quotas(
-		struct damon_sysfs_kdamond *kdamond)
+static int damon_sysfs_upd_schemes_effective_quotas(void *data)
 {
+	struct damon_sysfs_kdamond *kdamond = data;
 	struct damon_ctx *ctx = kdamond->damon_ctx;
 
-	if (!ctx)
-		return -EINVAL;
 	damos_sysfs_update_effective_quotas(
 			kdamond->contexts->contexts_arr[0]->schemes, ctx);
 	return 0;
@@ -1400,9 +1398,6 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 			damon_sysfs_schemes_regions_updating = false;
 		}
 		break;
-	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_EFFECTIVE_QUOTAS:
-		err = damon_sysfs_upd_schemes_effective_quotas(kdamond);
-		break;
 	default:
 		break;
 	}
@@ -1550,6 +1545,10 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
 		return damon_sysfs_schemes_clear_regions(
 			kdamond->contexts->contexts_arr[0]->schemes);
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_EFFECTIVE_QUOTAS:
+		return damon_sysfs_damon_call(
+				damon_sysfs_upd_schemes_effective_quotas,
+				kdamond);
 	default:
 		break;
 	}
-- 
2.39.5

[RFC PATCH 7/9] mm/damon/core: implement damos_walk()

[SeongJae Park]

Introduce a new core layer interface, damos_walk().  It aims to replace
some damon_callback usages that access DAMOS schemes applied regions of
ongoing kdamond with additional synchronizations.  It receives a
function pointer and asks kdamond to invoke it for any region that it will
apply any DAMOS action within one scheme apply interval for every scheme
of it.  The function further waits until the kdamond finishes the
invocations for every scheme, or cancels the request, and returns.

The kdamond invokes the function as requested within the main loop.  If
it is deactivated by DAMOS watermarks or going out of the main loop, it
marks the request as canceled, so that damos_walk() can wakeup and
return.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  33 ++++++++++-
 mm/damon/core.c       | 134 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 165 insertions(+), 2 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 529ea578f2d5..acedaab4dccf 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -368,6 +368,31 @@ struct damos_filter {
 	struct list_head list;
 };
 
+struct damon_ctx;
+struct damos;
+
+/**
+ * struct damos_walk_control - Control damos_walk().
+ *
+ * @walk_fn:	Function to be called back for each region.
+ * @data:	Data that will be passed to walk functions.
+ *
+ * Control damos_walk(), which requests specific kdamond to invoke the given
+ * function to each region that eligible to apply actions of the kdamond's
+ * schemes.  Refer to damos_walk() for more details.
+ */
+struct damos_walk_control {
+	void (*walk_fn)(void *data, struct damon_ctx *ctx,
+			struct damon_target *t, struct damon_region *r,
+			struct damos *s);
+	void *data;
+/* private: internal use only */
+	/* informs if the kdamond finished handling of the walk request */
+	struct completion completion;
+	/* informs if the walk is canceled. */
+	bool canceled;
+};
+
 /**
  * struct damos_access_pattern - Target access pattern of the given scheme.
  * @min_sz_region:	Minimum size of target regions.
@@ -453,6 +478,8 @@ struct damos {
 	 * @action
 	 */
 	unsigned long next_apply_sis;
+	/* informs if ongoing DAMOS walk for this scheme is finished */
+	bool walk_completed;
 /* public: */
 	struct damos_quota quota;
 	struct damos_watermarks wmarks;
@@ -480,8 +507,6 @@ enum damon_ops_id {
 	NR_DAMON_OPS,
 };
 
-struct damon_ctx;
-
 /**
  * struct damon_operations - Monitoring operations for given use cases.
  *
@@ -694,6 +719,9 @@ struct damon_ctx {
 	struct damon_call_control *call_control;
 	struct mutex call_control_lock;
 
+	struct damos_walk_control *walk_control;
+	struct mutex walk_control_lock;
+
 /* public: */
 	struct task_struct *kdamond;
 	struct mutex kdamond_lock;
@@ -842,6 +870,7 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive);
 int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
 
 int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
+int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
 
 int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 89a679c06e30..de923b3a1084 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -534,6 +534,7 @@ struct damon_ctx *damon_new_ctx(void)
 
 	mutex_init(&ctx->kdamond_lock);
 	mutex_init(&ctx->call_control_lock);
+	mutex_init(&ctx->walk_control_lock);
 
 	ctx->attrs.min_nr_regions = 10;
 	ctx->attrs.max_nr_regions = 1000;
@@ -1232,6 +1233,46 @@ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
 	return 0;
 }
 
+/**
+ * damos_walk() - Invoke a given functions while DAMOS walk regions.
+ * @ctx:	DAMON context to call the functions for.
+ * @control:	Control variable of the walk request.
+ *
+ * Ask DAMON worker thread (kdamond) of @ctx to call a function for each region
+ * that the kdamond will apply DAMOS action to, and wait until the kdamond
+ * finishes handling of the request.
+ *
+ * The kdamond executes the given function in the main loop, for each region
+ * just before it applies any DAMOS actions of @ctx to it.  The invocation is
+ * made only within one &damos->apply_interval_us since damos_walk()
+ * invocation, for each scheme.  The given callback function can hence safely
+ * access the internal data of &struct damon_ctx and &struct damon_region that
+ * each of the scheme will apply the action for next interval, without
+ * additional synchronizations against the kdamond.  If every scheme of @ctx
+ * passed at least one &damos->apply_interval_us, kdamond marks the request as
+ * completed so that damos_walk() can wakeup and return.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control)
+{
+	init_completion(&control->completion);
+	control->canceled = false;
+	mutex_lock(&ctx->walk_control_lock);
+	if (ctx->walk_control) {
+		mutex_unlock(&ctx->walk_control_lock);
+		return -EBUSY;
+	}
+	ctx->walk_control = control;
+	mutex_unlock(&ctx->walk_control_lock);
+	if (!damon_is_running(ctx))
+		return -EINVAL;
+	wait_for_completion(&control->completion);
+	if (control->canceled)
+		return -ECANCELED;
+	return 0;
+}
+
 /*
  * Reset the aggregated monitoring results ('nr_accesses' of each region).
  */
@@ -1411,6 +1452,93 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
 	return false;
 }
 
+/*
+ * damos_walk_call_walk() - Call &damos_walk_control->walk_fn.
+ * @ctx:	The context of &damon_ctx->walk_control.
+ * @t:		The monitoring target of @r that @s will be applied.
+ * @r:		The region of @t that @s will be applied.
+ * @s:		The scheme of @ctx that will be applied to @r.
+ *
+ * This function is called from kdamond whenever it found a region that
+ * eligible to apply a DAMOS scheme's action.  If a DAMOS walk request is
+ * installed by damos_walk() and its &damos_walk_control->walk_fn has not
+ * invoked for the region for the last &damos->apply_interval_us interval,
+ * invoke it.
+ */
+static void damos_walk_call_walk(struct damon_ctx *ctx, struct damon_target *t,
+		struct damon_region *r, struct damos *s)
+{
+	struct damos_walk_control *control;
+
+	mutex_lock(&ctx->walk_control_lock);
+	control = ctx->walk_control;
+	mutex_unlock(&ctx->walk_control_lock);
+	if (!control)
+		return;
+	control->walk_fn(control->data, ctx, t, r, s);
+}
+
+/*
+ * damos_walk_complete() - Complete DAMOS walk request if all walks are done.
+ * @ctx:	The context of &damon_ctx->walk_control.
+ * @s:		A scheme of @ctx that all walks are now done.
+ *
+ * This function is called when kdamond finished applying the action of a DAMOS
+ * scheme to regions that eligible for the given &damos->apply_interval_us.  If
+ * every scheme of @ctx including @s now finished walking for at least one
+ * &damos->apply_interval_us, this function makrs the handling of the given
+ * DAMOS walk request is done, so that damos_walk() can wake up and return.
+ */
+static void damos_walk_complete(struct damon_ctx *ctx, struct damos *s)
+{
+	struct damos *siter;
+	struct damos_walk_control *control;
+
+	mutex_lock(&ctx->walk_control_lock);
+	control = ctx->walk_control;
+	mutex_unlock(&ctx->walk_control_lock);
+	if (!control)
+		return;
+
+	s->walk_completed = true;
+	/* if all schemes completed, signal completion to walker */
+	damon_for_each_scheme(siter, ctx) {
+		if (!siter->walk_completed)
+			return;
+	}
+	complete(&control->completion);
+	mutex_lock(&ctx->walk_control_lock);
+	ctx->walk_control = NULL;
+	mutex_unlock(&ctx->walk_control_lock);
+}
+
+/*
+ * damos_walk_cancel() - Cancel the current DAMOS walk request.
+ * @ctx:	The context of &damon_ctx->walk_control.
+ *
+ * This function is called when @ctx is deactivated by DAMOS watermarks, DAMOS
+ * walk is requested but there is no DAMOS scheme to walk for, or the kdamond
+ * is already out of the main loop and therefore gonna be terminated, and hence
+ * cannot continue the walks.  This function therefore marks the walk request
+ * as canceled, so that damos_walk() can wake up and return.
+ */
+static void damos_walk_cancel(struct damon_ctx *ctx)
+{
+	struct damos_walk_control *control;
+
+	mutex_lock(&ctx->walk_control_lock);
+	control = ctx->walk_control;
+	mutex_unlock(&ctx->walk_control_lock);
+
+	if (!control)
+		return;
+	control->canceled = true;
+	complete(&control->completion);
+	mutex_lock(&ctx->walk_control_lock);
+	ctx->walk_control = NULL;
+	mutex_unlock(&ctx->walk_control_lock);
+}
+
 static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 		struct damon_region *r, struct damos *s)
 {
@@ -1467,6 +1595,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 		if (damos_filter_out(c, t, r, s))
 			return;
 		ktime_get_coarse_ts64(&begin);
+		damos_walk_call_walk(c, t, r, s);
 		if (c->callback.before_damos_apply)
 			err = c->callback.before_damos_apply(c, t, r, s);
 		if (!err) {
@@ -1745,6 +1874,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 	damon_for_each_scheme(s, c) {
 		if (c->passed_sample_intervals < s->next_apply_sis)
 			continue;
+		damos_walk_complete(c, s);
 		s->next_apply_sis = c->passed_sample_intervals +
 			(s->apply_interval_us ? s->apply_interval_us :
 			 c->attrs.aggr_interval) / sample_interval;
@@ -2077,6 +2207,7 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
 				ctx->callback.after_wmarks_check(ctx))
 			break;
 		kdamond_call(ctx, true);
+		damos_walk_cancel(ctx);
 	}
 	return -EBUSY;
 }
@@ -2171,6 +2302,8 @@ static int kdamond_fn(void *data)
 		 */
 		if (!list_empty(&ctx->schemes))
 			kdamond_apply_schemes(ctx);
+		else
+			damos_walk_cancel(ctx);
 
 		sample_interval = ctx->attrs.sample_interval ?
 			ctx->attrs.sample_interval : 1;
@@ -2211,6 +2344,7 @@ static int kdamond_fn(void *data)
 	mutex_unlock(&ctx->kdamond_lock);
 
 	kdamond_call(ctx, true);
+	damos_walk_cancel(ctx);
 
 	mutex_lock(&damon_lock);
 	nr_running_ctxs--;
-- 
2.39.5

[RFC PATCH 8/9] mm/damon/sysfs: use damos_walk() for update_schemes_tried_{bytes,regions}

[SeongJae Park]

DAMON sysfs interface uses damon_callback with its own complicated
synchronization facility to handle update_schemes_tried_bytes and
update_schemes_tried_regions commands.  But damos_walk() can support the
use case without the additional synchronizations.  Convert the code to
use damos_walk() instead.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-common.h  |  5 +++++
 mm/damon/sysfs-schemes.c | 48 ++++++++++++++++++++++++++++++++++++++++
 mm/damon/sysfs.c         | 43 +++++++++++++++++++++++++++++++++++
 3 files changed, 96 insertions(+)

diff --git a/mm/damon/sysfs-common.h b/mm/damon/sysfs-common.h
index e79b4a65ff2d..81f1c845118f 100644
--- a/mm/damon/sysfs-common.h
+++ b/mm/damon/sysfs-common.h
@@ -55,6 +55,11 @@ bool damos_sysfs_regions_upd_done(void);
 
 int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
 
+void damos_sysfs_populate_region_dir(struct damon_sysfs_schemes *sysfs_schemes,
+		struct damon_ctx *ctx, struct damon_target *t,
+		struct damon_region *r, struct damos *s,
+		bool total_bytes_only);
+
 int damon_sysfs_schemes_clear_regions(
 		struct damon_sysfs_schemes *sysfs_schemes);
 
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 6c8f9eae75af..404c21f45640 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2188,6 +2188,54 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 	return 0;
 }
 
+/**
+ * damos_sysfs_populate_region_dir() - Populate a schemes tried region dir.
+ * @sysfs_schemes:	Schemes directory to populate regions directory.
+ * @ctx:		Corresponding DAMON context.
+ * @t:			DAMON target of @r.
+ * @r:			DAMON region to populate the directory for.
+ * @s:			Corresponding scheme.
+ * @total_bytes_only:	Whether the request is for bytes update only.
+ *
+ * Called from DAMOS walk callback while holding damon_sysfs_lock.
+ */
+void damos_sysfs_populate_region_dir(struct damon_sysfs_schemes *sysfs_schemes,
+		struct damon_ctx *ctx, struct damon_target *t,
+		struct damon_region *r, struct damos *s, bool total_bytes_only)
+{
+	struct damos *scheme;
+	struct damon_sysfs_scheme_regions *sysfs_regions;
+	struct damon_sysfs_scheme_region *region;
+	int schemes_idx = 0;
+
+	damon_for_each_scheme(scheme, ctx) {
+		if (scheme == s)
+			break;
+		schemes_idx++;
+	}
+
+	/* user could have removed the scheme sysfs dir */
+	if (schemes_idx >= sysfs_schemes->nr)
+		return;
+
+	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
+	sysfs_regions->total_bytes += r->ar.end - r->ar.start;
+	if (total_bytes_only)
+		return;
+
+	region = damon_sysfs_scheme_region_alloc(r);
+	if (!region)
+		return;
+	list_add_tail(&region->list, &sysfs_regions->regions_list);
+	sysfs_regions->nr_regions++;
+	if (kobject_init_and_add(&region->kobj,
+				&damon_sysfs_scheme_region_ktype,
+				&sysfs_regions->kobj, "%d",
+				sysfs_regions->nr_regions++)) {
+		kobject_put(&region->kobj);
+	}
+}
+
 /*
  * DAMON callback that called after each accesses sampling.  While this
  * callback is registered, damon_sysfs_lock should be held to ensure the
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 978de4305f2b..dafeec20ac53 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1512,6 +1512,45 @@ static int damon_sysfs_damon_call(int (*fn)(void *data),
 	return damon_call(kdamond->damon_ctx, &call_control);
 }
 
+struct damon_sysfs_schemes_walk_data {
+	struct damon_sysfs_kdamond *sysfs_kdamond;
+	bool total_bytes_only;
+};
+
+/* populate the region directory */
+static void damon_sysfs_schemes_tried_regions_upd_one(void *data, struct damon_ctx *ctx,
+		struct damon_target *t, struct damon_region *r,
+		struct damos *s)
+{
+	struct damon_sysfs_schemes_walk_data *walk_data = data;
+	struct damon_sysfs_kdamond *sysfs_kdamond = walk_data->sysfs_kdamond;
+
+	damos_sysfs_populate_region_dir(
+			sysfs_kdamond->contexts->contexts_arr[0]->schemes,
+			ctx, t, r, s, walk_data->total_bytes_only);
+}
+
+static int damon_sysfs_update_schemes_tried_regions(
+		struct damon_sysfs_kdamond *sysfs_kdamond, bool total_bytes_only)
+{
+	struct damon_sysfs_schemes_walk_data walk_data = {
+		.sysfs_kdamond = sysfs_kdamond,
+		.total_bytes_only = total_bytes_only,
+	};
+	struct damos_walk_control control = {
+		.walk_fn = damon_sysfs_schemes_tried_regions_upd_one,
+		.data = &walk_data,
+	};
+	struct damon_ctx *ctx = sysfs_kdamond->damon_ctx;
+
+	if (!ctx)
+		return -EINVAL;
+
+	damon_sysfs_schemes_clear_regions(
+			sysfs_kdamond->contexts->contexts_arr[0]->schemes);
+	return damos_walk(ctx, &control);
+}
+
 /*
  * damon_sysfs_handle_cmd() - Handle a command for a specific kdamond.
  * @cmd:	The command to handle.
@@ -1542,6 +1581,10 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS:
 		return damon_sysfs_damon_call(
 				damon_sysfs_upd_schemes_stats, kdamond);
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES:
+		return damon_sysfs_update_schemes_tried_regions(kdamond, true);
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS:
+		return damon_sysfs_update_schemes_tried_regions(kdamond, false);
 	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
 		return damon_sysfs_schemes_clear_regions(
 			kdamond->contexts->contexts_arr[0]->schemes);
-- 
2.39.5

[RFC PATCH 9/9] mm/damon/sysfs: remove unused code for schemes tried regions update

[SeongJae Park]

DAMON sysfs interface was using damon_callback with its own complicated
synchronization logics to update DAMOS scheme applied regions
directories and files.  But it is replaced to use damos_walk(), and the
additional synchronization logics are no more being used.  Remove those.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-common.h  |  10 --
 mm/damon/sysfs-schemes.c | 204 ---------------------------------------
 mm/damon/sysfs.c         |  70 +-------------
 3 files changed, 2 insertions(+), 282 deletions(-)

diff --git a/mm/damon/sysfs-common.h b/mm/damon/sysfs-common.h
index 81f1c845118f..b3f63bc658b7 100644
--- a/mm/damon/sysfs-common.h
+++ b/mm/damon/sysfs-common.h
@@ -45,16 +45,6 @@ void damon_sysfs_schemes_update_stats(
 		struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx);
 
-int damon_sysfs_schemes_update_regions_start(
-		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx, bool total_bytes_only);
-
-void damos_sysfs_mark_finished_regions_updates(struct damon_ctx *ctx);
-
-bool damos_sysfs_regions_upd_done(void);
-
-int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
-
 void damos_sysfs_populate_region_dir(struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx, struct damon_target *t,
 		struct damon_region *r, struct damos *s,
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 404c21f45640..5000d81d0d83 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -114,55 +114,11 @@ static const struct kobj_type damon_sysfs_scheme_region_ktype = {
  * scheme regions directory
  */
 
-/*
- * enum damos_sysfs_regions_upd_status - Represent DAMOS tried regions update
- *					 status
- * @DAMOS_TRIED_REGIONS_UPD_IDLE:		Waiting for next request.
- * @DAMOS_TRIED_REGIONS_UPD_STARTED:		Update started.
- * @DAMOS_TRIED_REGIONS_UPD_FINISHED:	Update finished.
- *
- * Each DAMON-based operation scheme (&struct damos) has its own apply
- * interval, and we need to expose the scheme tried regions based on only
- * single snapshot.  For this, we keep the tried regions update status for each
- * scheme.  The status becomes 'idle' at the beginning.
- *
- * Once the tried regions update request is received, the request handling
- * start function (damon_sysfs_scheme_update_regions_start()) sets the status
- * of all schemes as 'idle' again, and register ->before_damos_apply()
- * callback.
- *
- * Then, the first followup ->before_damos_apply() callback
- * (damon_sysfs_before_damos_apply()) sets the status 'started'.  The first
- * ->after_sampling() or ->after_aggregation() callback
- *  (damon_sysfs_cmd_request_callback()) after the call is called only after
- *  the scheme is completely applied to the given snapshot.  Hence the callback
- *  knows the situation by showing 'started' status, and sets the status as
- *  'finished'.  Then, damon_sysfs_before_damos_apply() understands the
- *  situation by showing the 'finished' status and do nothing.
- *
- * If DAMOS is not applied to any region due to any reasons including the
- * access pattern, the watermarks, the quotas, and the filters,
- * ->before_damos_apply() will not be called back.  Until the situation is
- * changed, the update will not be finished.  To avoid this,
- * damon_sysfs_after_sampling() set the status as 'finished' if more than two
- * apply intervals of the scheme is passed while the state is 'idle'.
- *
- *  Finally, the tried regions request handling finisher function
- *  (damon_sysfs_schemes_update_regions_stop()) unregisters the callbacks.
- */
-enum damos_sysfs_regions_upd_status {
-	DAMOS_TRIED_REGIONS_UPD_IDLE,
-	DAMOS_TRIED_REGIONS_UPD_STARTED,
-	DAMOS_TRIED_REGIONS_UPD_FINISHED,
-};
-
 struct damon_sysfs_scheme_regions {
 	struct kobject kobj;
 	struct list_head regions_list;
 	int nr_regions;
 	unsigned long total_bytes;
-	enum damos_sysfs_regions_upd_status upd_status;
-	unsigned long upd_timeout_jiffies;
 };
 
 static struct damon_sysfs_scheme_regions *
@@ -178,7 +134,6 @@ damon_sysfs_scheme_regions_alloc(void)
 	INIT_LIST_HEAD(&regions->regions_list);
 	regions->nr_regions = 0;
 	regions->total_bytes = 0;
-	regions->upd_status = DAMOS_TRIED_REGIONS_UPD_IDLE;
 	return regions;
 }
 
@@ -2131,63 +2086,6 @@ void damon_sysfs_schemes_update_stats(
 	}
 }
 
-/*
- * damon_sysfs_schemes that need to update its schemes regions dir.  Protected
- * by damon_sysfs_lock
- */
-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
- * registered, damon_sysfs_lock should be held to ensure the regions
- * directories exist.
- */
-static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
-		struct damon_target *t, struct damon_region *r,
-		struct damos *s)
-{
-	struct damos *scheme;
-	struct damon_sysfs_scheme_regions *sysfs_regions;
-	struct damon_sysfs_scheme_region *region;
-	struct damon_sysfs_schemes *sysfs_schemes =
-		damon_sysfs_schemes_for_damos_callback;
-	int schemes_idx = 0;
-
-	damon_for_each_scheme(scheme, ctx) {
-		if (scheme == s)
-			break;
-		schemes_idx++;
-	}
-
-	/* user could have removed the scheme sysfs dir */
-	if (schemes_idx >= sysfs_schemes->nr)
-		return 0;
-
-	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
-	if (sysfs_regions->upd_status == DAMOS_TRIED_REGIONS_UPD_FINISHED)
-		return 0;
-	if (sysfs_regions->upd_status == DAMOS_TRIED_REGIONS_UPD_IDLE)
-		sysfs_regions->upd_status = DAMOS_TRIED_REGIONS_UPD_STARTED;
-	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);
-	if (!region)
-		return 0;
-	list_add_tail(&region->list, &sysfs_regions->regions_list);
-	sysfs_regions->nr_regions++;
-	if (kobject_init_and_add(&region->kobj,
-				&damon_sysfs_scheme_region_ktype,
-				&sysfs_regions->kobj, "%d",
-				damon_sysfs_schemes_region_idx++)) {
-		kobject_put(&region->kobj);
-	}
-	return 0;
-}
-
 /**
  * damos_sysfs_populate_region_dir() - Populate a schemes tried region dir.
  * @sysfs_schemes:	Schemes directory to populate regions directory.
@@ -2236,29 +2134,6 @@ void damos_sysfs_populate_region_dir(struct damon_sysfs_schemes *sysfs_schemes,
 	}
 }
 
-/*
- * DAMON callback that called after each accesses sampling.  While this
- * callback is registered, damon_sysfs_lock should be held to ensure the
- * regions directories exist.
- */
-void damos_sysfs_mark_finished_regions_updates(struct damon_ctx *ctx)
-{
-	struct damon_sysfs_schemes *sysfs_schemes =
-		damon_sysfs_schemes_for_damos_callback;
-	struct damon_sysfs_scheme_regions *sysfs_regions;
-	int i;
-
-	for (i = 0; i < sysfs_schemes->nr; i++) {
-		sysfs_regions = sysfs_schemes->schemes_arr[i]->tried_regions;
-		if (sysfs_regions->upd_status ==
-				DAMOS_TRIED_REGIONS_UPD_STARTED ||
-				time_after(jiffies,
-					sysfs_regions->upd_timeout_jiffies))
-			sysfs_regions->upd_status =
-				DAMOS_TRIED_REGIONS_UPD_FINISHED;
-	}
-}
-
 /* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
 int damon_sysfs_schemes_clear_regions(
 		struct damon_sysfs_schemes *sysfs_schemes)
@@ -2275,82 +2150,3 @@ int damon_sysfs_schemes_clear_regions(
 	}
 	return 0;
 }
-
-static struct damos *damos_sysfs_nth_scheme(int n, struct damon_ctx *ctx)
-{
-	struct damos *scheme;
-	int i = 0;
-
-	damon_for_each_scheme(scheme, ctx) {
-		if (i == n)
-			return scheme;
-		i++;
-	}
-	return NULL;
-}
-
-static void damos_tried_regions_init_upd_status(
-		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx)
-{
-	int i;
-	struct damos *scheme;
-	struct damon_sysfs_scheme_regions *sysfs_regions;
-
-	for (i = 0; i < sysfs_schemes->nr; i++) {
-		sysfs_regions = sysfs_schemes->schemes_arr[i]->tried_regions;
-		scheme = damos_sysfs_nth_scheme(i, ctx);
-		if (!scheme) {
-			sysfs_regions->upd_status =
-				DAMOS_TRIED_REGIONS_UPD_FINISHED;
-			continue;
-		}
-		sysfs_regions->upd_status = DAMOS_TRIED_REGIONS_UPD_IDLE;
-		sysfs_regions->upd_timeout_jiffies = jiffies +
-			2 * usecs_to_jiffies(scheme->apply_interval_us ?
-					scheme->apply_interval_us :
-					ctx->attrs.aggr_interval);
-	}
-}
-
-/* Called while damon_sysfs_lock is hold */
-int damon_sysfs_schemes_update_regions_start(
-		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx, bool total_bytes_only)
-{
-	damon_sysfs_schemes_clear_regions(sysfs_schemes);
-	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
-	damos_tried_regions_init_upd_status(sysfs_schemes, ctx);
-	damos_regions_upd_total_bytes_only = total_bytes_only;
-	ctx->callback.before_damos_apply = damon_sysfs_before_damos_apply;
-	return 0;
-}
-
-bool damos_sysfs_regions_upd_done(void)
-{
-	struct damon_sysfs_schemes *sysfs_schemes =
-		damon_sysfs_schemes_for_damos_callback;
-	struct damon_sysfs_scheme_regions *sysfs_regions;
-	int i;
-
-	for (i = 0; i < sysfs_schemes->nr; i++) {
-		sysfs_regions = sysfs_schemes->schemes_arr[i]->tried_regions;
-		if (sysfs_regions->upd_status !=
-				DAMOS_TRIED_REGIONS_UPD_FINISHED)
-			return false;
-	}
-	return true;
-}
-
-/*
- * Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock.  Caller
- * should unlock damon_sysfs_lock which held before
- * damon_sysfs_schemes_update_regions_start()
- */
-int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx)
-{
-	damon_sysfs_schemes_for_damos_callback = NULL;
-	ctx->callback.before_damos_apply = NULL;
-	damon_sysfs_schemes_region_idx = 0;
-	return 0;
-}
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index dafeec20ac53..77a9b8200e78 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1181,25 +1181,9 @@ static int damon_sysfs_add_targets(struct damon_ctx *ctx,
 	return 0;
 }
 
-static bool damon_sysfs_schemes_regions_updating;
-
 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;
-	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_regions_updating) {
-		damon_sysfs_schemes_update_regions_stop(ctx);
-		damon_sysfs_schemes_regions_updating = false;
-		mutex_unlock(&damon_sysfs_lock);
-	}
 
 	if (!damon_target_has_pid(ctx))
 		return;
@@ -1232,28 +1216,6 @@ static int damon_sysfs_upd_schemes_stats(void *data)
 	return 0;
 }
 
-static int damon_sysfs_upd_schemes_regions_start(
-		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,
-			total_bytes_only);
-}
-
-static int damon_sysfs_upd_schemes_regions_stop(
-		struct damon_sysfs_kdamond *kdamond)
-{
-	struct damon_ctx *ctx = kdamond->damon_ctx;
-
-	if (!ctx)
-		return -EINVAL;
-	return damon_sysfs_schemes_update_regions_stop(ctx);
-}
-
 static inline bool damon_sysfs_kdamond_running(
 		struct damon_sysfs_kdamond *kdamond)
 {
@@ -1358,12 +1320,10 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 		bool after_aggregation)
 {
 	struct damon_sysfs_kdamond *kdamond;
-	bool total_bytes_only = false;
 	int err = 0;
 
 	/* avoid deadlock due to concurrent state_store('off') */
-	if (!damon_sysfs_schemes_regions_updating &&
-			!mutex_trylock(&damon_sysfs_lock))
+	if (!mutex_trylock(&damon_sysfs_lock))
 		return 0;
 	kdamond = damon_sysfs_cmd_request.kdamond;
 	if (!kdamond || kdamond->damon_ctx != c)
@@ -1374,39 +1334,13 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c, bool active,
 			goto out;
 		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,
-					total_bytes_only);
-			if (!err) {
-				damon_sysfs_schemes_regions_updating = true;
-				goto keep_lock_out;
-			}
-		} else {
-			damos_sysfs_mark_finished_regions_updates(c);
-			/*
-			 * Continue regions updating if DAMON is till
-			 * active and the update for all schemes is not
-			 * finished.
-			 */
-			if (active && !damos_sysfs_regions_upd_done())
-				goto keep_lock_out;
-			err = damon_sysfs_upd_schemes_regions_stop(kdamond);
-			damon_sysfs_schemes_regions_updating = false;
-		}
-		break;
 	default:
 		break;
 	}
 	/* Mark the request as invalid now. */
 	damon_sysfs_cmd_request.kdamond = NULL;
 out:
-	if (!damon_sysfs_schemes_regions_updating)
-		mutex_unlock(&damon_sysfs_lock);
-keep_lock_out:
+	mutex_unlock(&damon_sysfs_lock);
 	return err;
 }
 
-- 
2.39.5