[PATCH 0/7] Implement Data Access Monitoring-based Memory Operation Schemes

[PATCH 0/7] Implement Data Access Monitoring-based Memory Operation Schemes

[SeongJae Park]

Changes from Previous Version (RFC[1])
======================================

- Rebase on latest -mm tree

[1] https://lore.kernel.org/linux-mm/20201216084404.23183-1-sjpark@amazon.com/

Introduction
============

DAMON[1] can be used as a primitive for data access aware memory management
optimizations.  For that, users who want such optimizations should run DAMON,
read the monitoring results, analyze it, plan a new memory management scheme,
and apply the new scheme by themselves.  Such efforts will be inevitable for
some complicated optimizations.

However, in many other cases, the users would simply want the system to apply a
memory management action to a memory region of a specific size having a
specific access frequency for a specific time.  For example, "page out a memory
region larger than 100 MiB keeping only rare accesses more than 2 minutes", or
"Do not use THP for a memory region larger than 2 MiB rarely accessed for more
than 1 seconds".

To make the works easier and non-redundant, this patchset implements a new
feature of DAMON, which is called Data Access Monitoring-based Operation
Schemes (DAMOS).  Using the feature, users can describe the normal schemes in a
simple way and ask DAMON to execute those on its own.

[1] https://damonitor.github.io

Evaluations
===========

DAMOS is accurate and useful for memory management optimizations.  An
experimental DAMON-based operation scheme for THP, 'ethp', removes 76.15% of
THP memory overheads while preserving 51.25% of THP speedup.  Another
experimental DAMON-based 'proactive reclamation' implementation, 'prcl',
reduces 93.38% of residential sets and 23.63% of system memory footprint while
incurring only 1.22% runtime overhead in the best case (parsec3/freqmine).

NOTE that the experimental THP optimization and proactive reclamation are not
for production but only for proof of concepts.

Please refer to the showcase web site's evaluation document[1] for detailed
evaluation setup and results.

[1] https://damonitor.github.io/doc/html/v34/vm/damon/eval.html

Baseline and Complete Git Tree
==============================

The patches are based on the latest -mm tree
(v5.15-rc3-mmots-2021-09-30-19-38)[1].  You can also clone the complete git
tree:

    $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git -b damos/patches/v1

The web is also available:
https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git/tag/?h=damos/patches/v1

[1] https://github.com/hnaz/linux-mm/tree/v5.15-rc3-mmots-2021-09-30-19-38

Development Trees
-----------------

There are a couple of trees for entire DAMON patchset series.

- For latest release: https://git.kernel.org/sj/h/damon/master
- For next release: https://git.kernel.org/sj/h/damon/next

Long-term Support Trees
-----------------------

For people who want to test DAMON but using LTS kernels, there are another
couple of trees based on two latest LTS kernels respectively and containing the
'damon/master' backports.

- For v5.4.y: https://git.kernel.org/sj/h/damon/for-v5.4.y
- For v5.10.y: https://git.kernel.org/sj/h/damon/for-v5.10.y

Sequence Of Patches
===================

The 1st patch accounts age of each region.  The 2nd patch implements the core
of the DAMON-based operation schemes feature.  The 3rd patch makes the default
monitoring primitives for virtual address spaces to support the schemes.  From
this point, the kernel space users can use DAMOS.  The 4th patch exports the
feature to the user space via the debugfs interface.  The 5th patch implements
schemes statistics feature for easier tuning of the schemes and runtime access
pattern analysis, and the 6th patch adds selftests for these changes.  Finally,
the 7th patch documents this new feature.

Patch History
=============

Changes from RFC v15.1
(https://lore.kernel.org/linux-mm/20201216084404.23183-1-sjpark@amazon.com/)
- Rebase on latest -mm tree

Please refer to RFC v15.1 for previous history.

SeongJae Park (7):
  mm/damon/core: Account age of target regions
  mm/damon/core: Implement DAMON-based Operation Schemes (DAMOS)
  mm/damon/vaddr: Support DAMON-based Operation Schemes
  mm/damon/dbgfs: Support DAMON-based Operation Schemes
  mm/damon/schemes: Implement statistics feature
  selftests/damon: Add 'schemes' debugfs tests
  Docs/admin-guide/mm/damon: Document DAMON-based Operation Schemes

 Documentation/admin-guide/mm/damon/start.rst  |  11 ++
 Documentation/admin-guide/mm/damon/usage.rst  |  51 +++++-
 include/linux/damon.h                         |  86 +++++++++
 mm/damon/core.c                               | 127 ++++++++++++++
 mm/damon/dbgfs.c                              | 166 +++++++++++++++++-
 mm/damon/vaddr.c                              |  58 ++++++
 .../testing/selftests/damon/debugfs_attrs.sh  |  13 ++
 7 files changed, 507 insertions(+), 5 deletions(-)

-- 
2.17.1

[PATCH 1/7] mm/damon/core: Account age of target regions

[SeongJae Park]

DAMON can be used for data access pattern aware memory management
optimizations.  For that, users should run DAMON, read the monitoring
results, analyze it, plan a new memory management scheme, and apply the
new scheme by themselves.  It would not be too hard, but still require
some level of effort.  For complicated cases, this effort is inevitable.

That said, in many cases, users would simply want to apply an actions to
a memory region of a specific size having a specific access frequency
for a specific time.  For example, "page out a memory region larger than
100 MiB but having a low access frequency more than 10 minutes", or "Use
THP for a memory region larger than 2 MiB having a high access frequency
for more than 2 seconds".

For such optimizations, users will need to first account the age of each
region themselves.  To reduce such efforts, this commit implements a
simple age account of each region in DAMON.  For each aggregation step,
DAMON compares the access frequency with that from last aggregation and
reset the age of the region if the change is significant.  Else, the age
is incremented.  Also, in case of the merge of regions, the region
size-weighted average of the ages is set as the age of merged new
region.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 10 ++++++++++
 mm/damon/core.c       | 13 +++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 755d70804705..3e8215debbd4 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -31,12 +31,22 @@ struct damon_addr_range {
  * @sampling_addr:	Address of the sample for the next access check.
  * @nr_accesses:	Access frequency of this region.
  * @list:		List head for siblings.
+ * @age:		Age of this region.
+ *
+ * @age is initially zero, increased for each aggregation interval, and reset
+ * to zero again if the access frequency is significantly changed.  If two
+ * regions are merged into a new region, both @nr_accesses and @age of the new
+ * region are set as region size-weighted average of those of the two regions.
  */
 struct damon_region {
 	struct damon_addr_range ar;
 	unsigned long sampling_addr;
 	unsigned int nr_accesses;
 	struct list_head list;
+
+	unsigned int age;
+/* private: Internal value for age calculation. */
+	unsigned int last_nr_accesses;
 };
 
 /**
diff --git a/mm/damon/core.c b/mm/damon/core.c
index d993db50280c..3efbe80779db 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -45,6 +45,9 @@ struct damon_region *damon_new_region(unsigned long start, unsigned long end)
 	region->nr_accesses = 0;
 	INIT_LIST_HEAD(&region->list);
 
+	region->age = 0;
+	region->last_nr_accesses = 0;
+
 	return region;
 }
 
@@ -444,6 +447,7 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
 
 		damon_for_each_region(r, t) {
 			trace_damon_aggregated(t, r, damon_nr_regions(t));
+			r->last_nr_accesses = r->nr_accesses;
 			r->nr_accesses = 0;
 		}
 	}
@@ -461,6 +465,7 @@ static void damon_merge_two_regions(struct damon_target *t,
 
 	l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
 			(sz_l + sz_r);
+	l->age = (l->age * sz_l + r->age * sz_r) / (sz_l + sz_r);
 	l->ar.end = r->ar.end;
 	damon_destroy_region(r, t);
 }
@@ -480,6 +485,11 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
 	struct damon_region *r, *prev = NULL, *next;
 
 	damon_for_each_region_safe(r, next, t) {
+		if (diff_of(r->nr_accesses, r->last_nr_accesses) > thres)
+			r->age = 0;
+		else
+			r->age++;
+
 		if (prev && prev->ar.end == r->ar.start &&
 		    diff_of(prev->nr_accesses, r->nr_accesses) <= thres &&
 		    sz_damon_region(prev) + sz_damon_region(r) <= sz_limit)
@@ -527,6 +537,9 @@ static void damon_split_region_at(struct damon_ctx *ctx,
 
 	r->ar.end = new->ar.start;
 
+	new->age = r->age;
+	new->last_nr_accesses = r->last_nr_accesses;
+
 	damon_insert_region(new, r, damon_next_region(r), t);
 }
 
-- 
2.17.1

[PATCH 2/7] mm/damon/core: Implement DAMON-based Operation Schemes (DAMOS)

[SeongJae Park]

In many cases, users might use DAMON for simple data access aware
memory management optimizations such as applying an operation scheme to
a memory region of a specific size having a specific access frequency
for a specific time.  For example, "page out a memory region larger than
100 MiB but having a low access frequency more than 10 minutes", or "Use
THP for a memory region larger than 2 MiB having a high access frequency
for more than 2 seconds".

Most simple form of the solution would be doing offline data access
pattern profiling using DAMON and modifying the application source code
or system configuration based on the profiling results.  Or, developing
a daemon constructed with two modules (one for access monitoring and the
other for applying memory management actions via mlock(), madvise(),
sysctl, etc) is imaginable.

To avoid users spending their time for implementation of such simple
data access monitoring-based operation schemes, this commit makes DAMON
to handle such schemes directly.  With this commit, users can simply
specify their desired schemes to DAMON.  Then, DAMON will automatically
apply the schemes to the user-specified target processes.

Each of the schemes is composed with conditions for filtering of the
target memory regions and desired memory management action for the
target.  Specifically, the format is::

    <min/max size> <min/max access frequency> <min/max age> <action>

The filtering conditions are size of memory region, number of accesses
to the region monitored by DAMON, and the age of the region.  The age of
region is incremented periodically but reset when its addresses or
access frequency has significantly changed or the action of a scheme was
applied.  For the action, current implementation supports a few of
madvise()-like hints, ``WILLNEED``, ``COLD``, ``PAGEOUT``, ``HUGEPAGE``,
and ``NOHUGEPAGE``.

Because DAMON supports various address spaces and application of the
actions to a monitoring target region is dependent to the type of the
target address space, the application code should be implemented by each
primitives and registered to the framework.  Note that this commit only
implements the framework part.  Following commit will implement the
action applications for virtual address spaces primitives.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  66 +++++++++++++++++++++++++
 mm/damon/core.c       | 109 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 175 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 3e8215debbd4..dbe18b0fb795 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -69,6 +69,48 @@ struct damon_target {
 	struct list_head list;
 };
 
+/**
+ * enum damos_action - Represents an action of a Data Access Monitoring-based
+ * Operation Scheme.
+ *
+ * @DAMOS_WILLNEED:	Call ``madvise()`` for the region with MADV_WILLNEED.
+ * @DAMOS_COLD:		Call ``madvise()`` for the region with MADV_COLD.
+ * @DAMOS_PAGEOUT:	Call ``madvise()`` for the region with MADV_PAGEOUT.
+ * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
+ * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
+ */
+enum damos_action {
+	DAMOS_WILLNEED,
+	DAMOS_COLD,
+	DAMOS_PAGEOUT,
+	DAMOS_HUGEPAGE,
+	DAMOS_NOHUGEPAGE,
+};
+
+/**
+ * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
+ * @min_sz_region:	Minimum size of target regions.
+ * @max_sz_region:	Maximum size of target regions.
+ * @min_nr_accesses:	Minimum ``->nr_accesses`` of target regions.
+ * @max_nr_accesses:	Maximum ``->nr_accesses`` of target regions.
+ * @min_age_region:	Minimum age of target regions.
+ * @max_age_region:	Maximum age of target regions.
+ * @action:		&damo_action to be applied to the target regions.
+ * @list:		List head for siblings.
+ *
+ * Note that both the minimums and the maximums are inclusive.
+ */
+struct damos {
+	unsigned long min_sz_region;
+	unsigned long max_sz_region;
+	unsigned int min_nr_accesses;
+	unsigned int max_nr_accesses;
+	unsigned int min_age_region;
+	unsigned int max_age_region;
+	enum damos_action action;
+	struct list_head list;
+};
+
 struct damon_ctx;
 
 /**
@@ -79,6 +121,7 @@ struct damon_ctx;
  * @prepare_access_checks:	Prepare next access check of target regions.
  * @check_accesses:		Check the accesses to target regions.
  * @reset_aggregated:		Reset aggregated accesses monitoring results.
+ * @apply_scheme:		Apply a DAMON-based operation scheme.
  * @target_valid:		Determine if the target is valid.
  * @cleanup:			Clean up the context.
  *
@@ -104,6 +147,9 @@ struct damon_ctx;
  * of its update.  The value will be used for regions adjustment threshold.
  * @reset_aggregated should reset the access monitoring results that aggregated
  * by @check_accesses.
+ * @apply_scheme is called from @kdamond when a region for user provided
+ * DAMON-based operation scheme is found.  It should apply the scheme's action
+ * to the region.  This is not used for &DAMON_ARBITRARY_TARGET case.
  * @target_valid should check whether the target is still valid for the
  * monitoring.
  * @cleanup is called from @kdamond just before its termination.
@@ -114,6 +160,8 @@ struct damon_primitive {
 	void (*prepare_access_checks)(struct damon_ctx *context);
 	unsigned int (*check_accesses)(struct damon_ctx *context);
 	void (*reset_aggregated)(struct damon_ctx *context);
+	int (*apply_scheme)(struct damon_ctx *context, struct damon_target *t,
+			struct damon_region *r, struct damos *scheme);
 	bool (*target_valid)(void *target);
 	void (*cleanup)(struct damon_ctx *context);
 };
@@ -192,6 +240,7 @@ struct damon_callback {
  * @min_nr_regions:	The minimum number of adaptive monitoring regions.
  * @max_nr_regions:	The maximum number of adaptive monitoring regions.
  * @adaptive_targets:	Head of monitoring targets (&damon_target) list.
+ * @schemes:		Head of schemes (&damos) list.
  */
 struct damon_ctx {
 	unsigned long sample_interval;
@@ -213,6 +262,7 @@ struct damon_ctx {
 	unsigned long min_nr_regions;
 	unsigned long max_nr_regions;
 	struct list_head adaptive_targets;
+	struct list_head schemes;
 };
 
 #define damon_next_region(r) \
@@ -233,6 +283,12 @@ struct damon_ctx {
 #define damon_for_each_target_safe(t, next, ctx)	\
 	list_for_each_entry_safe(t, next, &(ctx)->adaptive_targets, list)
 
+#define damon_for_each_scheme(s, ctx) \
+	list_for_each_entry(s, &(ctx)->schemes, list)
+
+#define damon_for_each_scheme_safe(s, next, ctx) \
+	list_for_each_entry_safe(s, next, &(ctx)->schemes, list)
+
 #ifdef CONFIG_DAMON
 
 struct damon_region *damon_new_region(unsigned long start, unsigned long end);
@@ -242,6 +298,14 @@ inline void damon_insert_region(struct damon_region *r,
 void damon_add_region(struct damon_region *r, struct damon_target *t);
 void damon_destroy_region(struct damon_region *r, struct damon_target *t);
 
+struct damos *damon_new_scheme(
+		unsigned long min_sz_region, unsigned long max_sz_region,
+		unsigned int min_nr_accesses, unsigned int max_nr_accesses,
+		unsigned int min_age_region, unsigned int max_age_region,
+		enum damos_action action);
+void damon_add_scheme(struct damon_ctx *ctx, struct damos *s);
+void damon_destroy_scheme(struct damos *s);
+
 struct damon_target *damon_new_target(unsigned long id);
 void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
 void damon_free_target(struct damon_target *t);
@@ -255,6 +319,8 @@ int damon_set_targets(struct damon_ctx *ctx,
 int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
 		unsigned long aggr_int, unsigned long primitive_upd_int,
 		unsigned long min_nr_reg, unsigned long max_nr_reg);
+int damon_set_schemes(struct damon_ctx *ctx,
+			struct damos **schemes, ssize_t nr_schemes);
 int damon_nr_running_ctxs(void);
 
 int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3efbe80779db..0ed97b21cbb6 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -85,6 +85,50 @@ void damon_destroy_region(struct damon_region *r, struct damon_target *t)
 	damon_free_region(r);
 }
 
+struct damos *damon_new_scheme(
+		unsigned long min_sz_region, unsigned long max_sz_region,
+		unsigned int min_nr_accesses, unsigned int max_nr_accesses,
+		unsigned int min_age_region, unsigned int max_age_region,
+		enum damos_action action)
+{
+	struct damos *scheme;
+
+	scheme = kmalloc(sizeof(*scheme), GFP_KERNEL);
+	if (!scheme)
+		return NULL;
+	scheme->min_sz_region = min_sz_region;
+	scheme->max_sz_region = max_sz_region;
+	scheme->min_nr_accesses = min_nr_accesses;
+	scheme->max_nr_accesses = max_nr_accesses;
+	scheme->min_age_region = min_age_region;
+	scheme->max_age_region = max_age_region;
+	scheme->action = action;
+	INIT_LIST_HEAD(&scheme->list);
+
+	return scheme;
+}
+
+void damon_add_scheme(struct damon_ctx *ctx, struct damos *s)
+{
+	list_add_tail(&s->list, &ctx->schemes);
+}
+
+static void damon_del_scheme(struct damos *s)
+{
+	list_del(&s->list);
+}
+
+static void damon_free_scheme(struct damos *s)
+{
+	kfree(s);
+}
+
+void damon_destroy_scheme(struct damos *s)
+{
+	damon_del_scheme(s);
+	damon_free_scheme(s);
+}
+
 /*
  * Construct a damon_target struct
  *
@@ -156,6 +200,7 @@ struct damon_ctx *damon_new_ctx(void)
 	ctx->max_nr_regions = 1000;
 
 	INIT_LIST_HEAD(&ctx->adaptive_targets);
+	INIT_LIST_HEAD(&ctx->schemes);
 
 	return ctx;
 }
@@ -175,7 +220,13 @@ static void damon_destroy_targets(struct damon_ctx *ctx)
 
 void damon_destroy_ctx(struct damon_ctx *ctx)
 {
+	struct damos *s, *next_s;
+
 	damon_destroy_targets(ctx);
+
+	damon_for_each_scheme_safe(s, next_s, ctx)
+		damon_destroy_scheme(s);
+
 	kfree(ctx);
 }
 
@@ -250,6 +301,30 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
 	return 0;
 }
 
+/**
+ * damon_set_schemes() - Set data access monitoring based operation schemes.
+ * @ctx:	monitoring context
+ * @schemes:	array of the schemes
+ * @nr_schemes:	number of entries in @schemes
+ *
+ * This function should not be called while the kdamond of the context is
+ * running.
+ *
+ * Return: 0 if success, or negative error code otherwise.
+ */
+int damon_set_schemes(struct damon_ctx *ctx, struct damos **schemes,
+			ssize_t nr_schemes)
+{
+	struct damos *s, *next;
+	ssize_t i;
+
+	damon_for_each_scheme_safe(s, next, ctx)
+		damon_destroy_scheme(s);
+	for (i = 0; i < nr_schemes; i++)
+		damon_add_scheme(ctx, schemes[i]);
+	return 0;
+}
+
 /**
  * damon_nr_running_ctxs() - Return number of currently running contexts.
  */
@@ -453,6 +528,39 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
 	}
 }
 
+static void damon_do_apply_schemes(struct damon_ctx *c,
+				   struct damon_target *t,
+				   struct damon_region *r)
+{
+	struct damos *s;
+	unsigned long sz;
+
+	damon_for_each_scheme(s, c) {
+		sz = r->ar.end - r->ar.start;
+		if (sz < s->min_sz_region || s->max_sz_region < sz)
+			continue;
+		if (r->nr_accesses < s->min_nr_accesses ||
+				s->max_nr_accesses < r->nr_accesses)
+			continue;
+		if (r->age < s->min_age_region || s->max_age_region < r->age)
+			continue;
+		if (c->primitive.apply_scheme)
+			c->primitive.apply_scheme(c, t, r, s);
+		r->age = 0;
+	}
+}
+
+static void kdamond_apply_schemes(struct damon_ctx *c)
+{
+	struct damon_target *t;
+	struct damon_region *r;
+
+	damon_for_each_target(t, c) {
+		damon_for_each_region(r, t)
+			damon_do_apply_schemes(c, t, r);
+	}
+}
+
 #define sz_damon_region(r) (r->ar.end - r->ar.start)
 
 /*
@@ -693,6 +801,7 @@ static int kdamond_fn(void *data)
 			if (ctx->callback.after_aggregation &&
 					ctx->callback.after_aggregation(ctx))
 				set_kdamond_stop(ctx);
+			kdamond_apply_schemes(ctx);
 			kdamond_reset_aggregated(ctx);
 			kdamond_split_regions(ctx);
 			if (ctx->primitive.reset_aggregated)
-- 
2.17.1

[PATCH 3/7] mm/damon/vaddr: Support DAMON-based Operation Schemes

[SeongJae Park]

This commit makes DAMON's default primitives for virtual address spaces
to support DAMON-based Operation Schemes (DAMOS) by implementing actions
application functions and registering it to the monitoring context.  The
implementation simply links 'madvise()' for related DAMOS actions.  That
is, 'madvise(MADV_WILLNEED)' is called for 'WILLNEED' DAMOS action and
similar for other actions ('COLD', 'PAGEOUT', 'HUGEPAGE', 'NOHUGEPAGE').

So, the kernel space DAMON users can now use the DAMON-based
optimizations with only small amount of code.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  2 ++
 mm/damon/vaddr.c      | 56 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index dbe18b0fb795..be6b6e81e8ee 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -337,6 +337,8 @@ void damon_va_prepare_access_checks(struct damon_ctx *ctx);
 unsigned int damon_va_check_accesses(struct damon_ctx *ctx);
 bool damon_va_target_valid(void *t);
 void damon_va_cleanup(struct damon_ctx *ctx);
+int damon_va_apply_scheme(struct damon_ctx *context, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme);
 void damon_va_set_primitives(struct damon_ctx *ctx);
 
 #endif	/* CONFIG_DAMON_VADDR */
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 58c1fb2aafa9..3e1c74d36bab 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -7,6 +7,7 @@
 
 #define pr_fmt(fmt) "damon-va: " fmt
 
+#include <asm-generic/mman-common.h>
 #include <linux/damon.h>
 #include <linux/hugetlb.h>
 #include <linux/mm.h>
@@ -658,6 +659,60 @@ bool damon_va_target_valid(void *target)
 	return false;
 }
 
+#ifndef CONFIG_ADVISE_SYSCALLS
+static int damos_madvise(struct damon_target *target, struct damon_region *r,
+			int behavior)
+{
+	return -EINVAL;
+}
+#else
+static int damos_madvise(struct damon_target *target, struct damon_region *r,
+			int behavior)
+{
+	struct mm_struct *mm;
+	int ret = -ENOMEM;
+
+	mm = damon_get_mm(target);
+	if (!mm)
+		goto out;
+
+	ret = do_madvise(mm, PAGE_ALIGN(r->ar.start),
+			PAGE_ALIGN(r->ar.end - r->ar.start), behavior);
+	mmput(mm);
+out:
+	return ret;
+}
+#endif	/* CONFIG_ADVISE_SYSCALLS */
+
+int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme)
+{
+	int madv_action;
+
+	switch (scheme->action) {
+	case DAMOS_WILLNEED:
+		madv_action = MADV_WILLNEED;
+		break;
+	case DAMOS_COLD:
+		madv_action = MADV_COLD;
+		break;
+	case DAMOS_PAGEOUT:
+		madv_action = MADV_PAGEOUT;
+		break;
+	case DAMOS_HUGEPAGE:
+		madv_action = MADV_HUGEPAGE;
+		break;
+	case DAMOS_NOHUGEPAGE:
+		madv_action = MADV_NOHUGEPAGE;
+		break;
+	default:
+		pr_warn("Wrong action %d\n", scheme->action);
+		return -EINVAL;
+	}
+
+	return damos_madvise(t, r, madv_action);
+}
+
 void damon_va_set_primitives(struct damon_ctx *ctx)
 {
 	ctx->primitive.init = damon_va_init;
@@ -667,6 +722,7 @@ void damon_va_set_primitives(struct damon_ctx *ctx)
 	ctx->primitive.reset_aggregated = NULL;
 	ctx->primitive.target_valid = damon_va_target_valid;
 	ctx->primitive.cleanup = NULL;
+	ctx->primitive.apply_scheme = damon_va_apply_scheme;
 }
 
 #include "vaddr-test.h"
-- 
2.17.1

[PATCH 4/7] mm/damon/dbgfs: Support DAMON-based Operation Schemes

[SeongJae Park]

This commit makes 'damon-dbgfs' to support the data access monitoring
oriented memory management schemes.  Users can read and update the
schemes using ``<debugfs>/damon/schemes`` file.  The format is::

    <min/max size> <min/max access frequency> <min/max age> <action>

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs.c | 165 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 162 insertions(+), 3 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index faee070977d8..78b7a04490c5 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -98,6 +98,159 @@ static ssize_t dbgfs_attrs_write(struct file *file,
 	return ret;
 }
 
+static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
+{
+	struct damos *s;
+	int written = 0;
+	int rc;
+
+	damon_for_each_scheme(s, c) {
+		rc = scnprintf(&buf[written], len - written,
+				"%lu %lu %u %u %u %u %d\n",
+				s->min_sz_region, s->max_sz_region,
+				s->min_nr_accesses, s->max_nr_accesses,
+				s->min_age_region, s->max_age_region,
+				s->action);
+		if (!rc)
+			return -ENOMEM;
+
+		written += rc;
+	}
+	return written;
+}
+
+static ssize_t dbgfs_schemes_read(struct file *file, char __user *buf,
+		size_t count, loff_t *ppos)
+{
+	struct damon_ctx *ctx = file->private_data;
+	char *kbuf;
+	ssize_t len;
+
+	kbuf = kmalloc(count, GFP_KERNEL);
+	if (!kbuf)
+		return -ENOMEM;
+
+	mutex_lock(&ctx->kdamond_lock);
+	len = sprint_schemes(ctx, kbuf, count);
+	mutex_unlock(&ctx->kdamond_lock);
+	if (len < 0)
+		goto out;
+	len = simple_read_from_buffer(buf, count, ppos, kbuf, len);
+
+out:
+	kfree(kbuf);
+	return len;
+}
+
+static void free_schemes_arr(struct damos **schemes, ssize_t nr_schemes)
+{
+	ssize_t i;
+
+	for (i = 0; i < nr_schemes; i++)
+		kfree(schemes[i]);
+	kfree(schemes);
+}
+
+static bool damos_action_valid(int action)
+{
+	switch (action) {
+	case DAMOS_WILLNEED:
+	case DAMOS_COLD:
+	case DAMOS_PAGEOUT:
+	case DAMOS_HUGEPAGE:
+	case DAMOS_NOHUGEPAGE:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/*
+ * Converts a string into an array of struct damos pointers
+ *
+ * Returns an array of struct damos pointers that converted if the conversion
+ * success, or NULL otherwise.
+ */
+static struct damos **str_to_schemes(const char *str, ssize_t len,
+				ssize_t *nr_schemes)
+{
+	struct damos *scheme, **schemes;
+	const int max_nr_schemes = 256;
+	int pos = 0, parsed, ret;
+	unsigned long min_sz, max_sz;
+	unsigned int min_nr_a, max_nr_a, min_age, max_age;
+	unsigned int action;
+
+	schemes = kmalloc_array(max_nr_schemes, sizeof(scheme),
+			GFP_KERNEL);
+	if (!schemes)
+		return NULL;
+
+	*nr_schemes = 0;
+	while (pos < len && *nr_schemes < max_nr_schemes) {
+		ret = sscanf(&str[pos], "%lu %lu %u %u %u %u %u%n",
+				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
+				&min_age, &max_age, &action, &parsed);
+		if (ret != 7)
+			break;
+		if (!damos_action_valid(action)) {
+			pr_err("wrong action %d\n", action);
+			goto fail;
+		}
+
+		pos += parsed;
+		scheme = damon_new_scheme(min_sz, max_sz, min_nr_a, max_nr_a,
+				min_age, max_age, action);
+		if (!scheme)
+			goto fail;
+
+		schemes[*nr_schemes] = scheme;
+		*nr_schemes += 1;
+	}
+	return schemes;
+fail:
+	free_schemes_arr(schemes, *nr_schemes);
+	return NULL;
+}
+
+static ssize_t dbgfs_schemes_write(struct file *file, const char __user *buf,
+		size_t count, loff_t *ppos)
+{
+	struct damon_ctx *ctx = file->private_data;
+	char *kbuf;
+	struct damos **schemes;
+	ssize_t nr_schemes = 0, ret = count;
+	int err;
+
+	kbuf = user_input_str(buf, count, ppos);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
+
+	schemes = str_to_schemes(kbuf, ret, &nr_schemes);
+	if (!schemes) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	mutex_lock(&ctx->kdamond_lock);
+	if (ctx->kdamond) {
+		ret = -EBUSY;
+		goto unlock_out;
+	}
+
+	err = damon_set_schemes(ctx, schemes, nr_schemes);
+	if (err)
+		ret = err;
+	else
+		nr_schemes = 0;
+unlock_out:
+	mutex_unlock(&ctx->kdamond_lock);
+	free_schemes_arr(schemes, nr_schemes);
+out:
+	kfree(kbuf);
+	return ret;
+}
+
 static inline bool targetid_is_pid(const struct damon_ctx *ctx)
 {
 	return ctx->primitive.target_valid == damon_va_target_valid;
@@ -279,6 +432,12 @@ static const struct file_operations attrs_fops = {
 	.write = dbgfs_attrs_write,
 };
 
+static const struct file_operations schemes_fops = {
+	.open = damon_dbgfs_open,
+	.read = dbgfs_schemes_read,
+	.write = dbgfs_schemes_write,
+};
+
 static const struct file_operations target_ids_fops = {
 	.open = damon_dbgfs_open,
 	.read = dbgfs_target_ids_read,
@@ -292,10 +451,10 @@ static const struct file_operations kdamond_pid_fops = {
 
 static void dbgfs_fill_ctx_dir(struct dentry *dir, struct damon_ctx *ctx)
 {
-	const char * const file_names[] = {"attrs", "target_ids",
+	const char * const file_names[] = {"attrs", "schemes", "target_ids",
 		"kdamond_pid"};
-	const struct file_operations *fops[] = {&attrs_fops, &target_ids_fops,
-		&kdamond_pid_fops};
+	const struct file_operations *fops[] = {&attrs_fops, &schemes_fops,
+		&target_ids_fops, &kdamond_pid_fops};
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(file_names); i++)
-- 
2.17.1

[PATCH 5/7] mm/damon/schemes: Implement statistics feature

[SeongJae Park]

To tune the DAMON-based operation schemes, knowing how many and how
large regions are affected by each of the schemes will be helful.  Those
stats could be used for not only the tuning, but also monitoring of the
working set size and the number of regions, if the scheme does not
change the program behavior too much.

For the reason, this commit implements the statistics for the schemes.
The total number and size of the regions that each scheme is applied are
exported to users via '->stat_count' and '->stat_sz' of 'struct damos'.
Admins can also check the number by reading 'schemes' debugfs file.  The
last two integers now represents the stats.  To allow collecting the
stats without changing the program behavior, this commit also adds new
scheme action, 'DAMOS_STAT'.  Note that 'DAMOS_STAT' is not only making
no memory operation actions, but also does not reset the age of regions.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 10 +++++++++-
 mm/damon/core.c       |  7 ++++++-
 mm/damon/dbgfs.c      |  5 +++--
 mm/damon/vaddr.c      |  2 ++
 4 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index be6b6e81e8ee..f301bb53381c 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -78,6 +78,7 @@ struct damon_target {
  * @DAMOS_PAGEOUT:	Call ``madvise()`` for the region with MADV_PAGEOUT.
  * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
  * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
+ * @DAMOS_STAT:		Do nothing but count the stat.
  */
 enum damos_action {
 	DAMOS_WILLNEED,
@@ -85,6 +86,7 @@ enum damos_action {
 	DAMOS_PAGEOUT,
 	DAMOS_HUGEPAGE,
 	DAMOS_NOHUGEPAGE,
+	DAMOS_STAT,		/* Do nothing but only record the stat */
 };
 
 /**
@@ -96,9 +98,13 @@ enum damos_action {
  * @min_age_region:	Minimum age of target regions.
  * @max_age_region:	Maximum age of target regions.
  * @action:		&damo_action to be applied to the target regions.
+ * @stat_count:		Total number of regions that this scheme is applied.
+ * @stat_sz:		Total size of regions that this scheme is applied.
  * @list:		List head for siblings.
  *
- * Note that both the minimums and the maximums are inclusive.
+ * For each aggregation interval, DAMON applies @action to monitoring target
+ * regions fit in the condition and updates the statistics.  Note that both
+ * the minimums and the maximums are inclusive.
  */
 struct damos {
 	unsigned long min_sz_region;
@@ -108,6 +114,8 @@ struct damos {
 	unsigned int min_age_region;
 	unsigned int max_age_region;
 	enum damos_action action;
+	unsigned long stat_count;
+	unsigned long stat_sz;
 	struct list_head list;
 };
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 0ed97b21cbb6..2f6785737902 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -103,6 +103,8 @@ struct damos *damon_new_scheme(
 	scheme->min_age_region = min_age_region;
 	scheme->max_age_region = max_age_region;
 	scheme->action = action;
+	scheme->stat_count = 0;
+	scheme->stat_sz = 0;
 	INIT_LIST_HEAD(&scheme->list);
 
 	return scheme;
@@ -544,9 +546,12 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			continue;
 		if (r->age < s->min_age_region || s->max_age_region < r->age)
 			continue;
+		s->stat_count++;
+		s->stat_sz += sz;
 		if (c->primitive.apply_scheme)
 			c->primitive.apply_scheme(c, t, r, s);
-		r->age = 0;
+		if (s->action != DAMOS_STAT)
+			r->age = 0;
 	}
 }
 
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 78b7a04490c5..28d6abf27763 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -106,11 +106,11 @@ static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 
 	damon_for_each_scheme(s, c) {
 		rc = scnprintf(&buf[written], len - written,
-				"%lu %lu %u %u %u %u %d\n",
+				"%lu %lu %u %u %u %u %d %lu %lu\n",
 				s->min_sz_region, s->max_sz_region,
 				s->min_nr_accesses, s->max_nr_accesses,
 				s->min_age_region, s->max_age_region,
-				s->action);
+				s->action, s->stat_count, s->stat_sz);
 		if (!rc)
 			return -ENOMEM;
 
@@ -159,6 +159,7 @@ static bool damos_action_valid(int action)
 	case DAMOS_PAGEOUT:
 	case DAMOS_HUGEPAGE:
 	case DAMOS_NOHUGEPAGE:
+	case DAMOS_STAT:
 		return true;
 	default:
 		return false;
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 3e1c74d36bab..953c145b4f08 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -705,6 +705,8 @@ int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 	case DAMOS_NOHUGEPAGE:
 		madv_action = MADV_NOHUGEPAGE;
 		break;
+	case DAMOS_STAT:
+		return 0;
 	default:
 		pr_warn("Wrong action %d\n", scheme->action);
 		return -EINVAL;
-- 
2.17.1

[PATCH 6/7] selftests/damon: Add 'schemes' debugfs tests

[SeongJae Park]

This commit adds simple selftets for 'schemes' debugfs file of DAMON.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/debugfs_attrs.sh | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/testing/selftests/damon/debugfs_attrs.sh b/tools/testing/selftests/damon/debugfs_attrs.sh
index bfabb19dc0d3..639cfb6a1f65 100755
--- a/tools/testing/selftests/damon/debugfs_attrs.sh
+++ b/tools/testing/selftests/damon/debugfs_attrs.sh
@@ -57,6 +57,19 @@ test_write_fail "$file" "1 2 3 5 4" "$orig_content" \
 test_content "$file" "$orig_content" "1 2 3 4 5" "successfully written"
 echo "$orig_content" > "$file"
 
+# Test schemes file
+# =================
+
+file="$DBGFS/schemes"
+orig_content=$(cat "$file")
+
+test_write_succ "$file" "1 2 3 4 5 6 4" \
+	"$orig_content" "valid input"
+test_write_fail "$file" "1 2
+3 4 5 6 3" "$orig_content" "multi lines"
+test_write_succ "$file" "" "$orig_content" "disabling"
+echo "$orig_content" > "$file"
+
 # Test target_ids file
 # ====================
 
-- 
2.17.1

[PATCH 7/7] Docs/admin-guide/mm/damon: Document DAMON-based Operation Schemes

[SeongJae Park]

This commit add description of DAMON-based operation schemes in the
DAMON documents.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/start.rst | 11 +++++
 Documentation/admin-guide/mm/damon/usage.rst | 51 +++++++++++++++++++-
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/start.rst b/Documentation/admin-guide/mm/damon/start.rst
index 9b313a66298d..e6a6d8ba51c3 100644
--- a/Documentation/admin-guide/mm/damon/start.rst
+++ b/Documentation/admin-guide/mm/damon/start.rst
@@ -108,6 +108,17 @@ the results as separate image files. ::
 You can show the images in a web page [1]_ .  Those made with other realistic
 workloads are also available [2]_ [3]_ [4]_.
 
+
+Data Access Pattern Aware Memory Management
+===========================================
+
+Below three commands make every memory region of size >=4K that doesn't
+accessed for >=60 seconds in your workload to be swapped out. ::
+
+    $ echo "#min-size max-size min-acc max-acc min-age max-age action" > scheme
+    $ echo "4K        max      0       0       60s     max     pageout" >> scheme
+    $ damo schemes -c my_thp_scheme <pid of your workload>
+
 .. [1] https://damonitor.github.io/doc/html/v17/admin-guide/mm/damon/start.html#visualizing-recorded-patterns
 .. [2] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.1.png.html
 .. [3] https://damonitor.github.io/test/result/visual/latest/rec.wss_sz.png.html
diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index a72cda374aba..c0296c14babf 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -34,8 +34,8 @@ the reason, this document describes only the debugfs interface
 debugfs Interface
 =================
 
-DAMON exports three files, ``attrs``, ``target_ids``, and ``monitor_on`` under
-its debugfs directory, ``<debugfs>/damon/``.
+DAMON exports four files, ``attrs``, ``target_ids``, ``schemes`` and
+``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.
 
 
 Attributes
@@ -74,6 +74,53 @@ check it again::
 Note that setting the target ids doesn't start the monitoring.
 
 
+Schemes
+-------
+
+For usual DAMON-based data access aware memory management optimizations, users
+would simply want the system to apply a memory management action to a memory
+region of a specific size having a specific access frequency for a specific
+time.  DAMON receives such formalized operation schemes from the user and
+applies those to the target processes.  It also counts the total number and
+size of regions that each scheme is applied.  This statistics can be used for
+online analysis or tuning of the schemes.
+
+Users can get and set the schemes by reading from and writing to ``schemes``
+debugfs file.  Reading the file also shows the statistics of each scheme.  To
+the file, each of the schemes should be represented in each line in below form:
+
+    min-size max-size min-acc max-acc min-age max-age action
+
+Note that the ranges are closed interval.  Bytes for the size of regions
+(``min-size`` and ``max-size``), number of monitored accesses per aggregate
+interval for access frequency (``min-acc`` and ``max-acc``), number of
+aggregate intervals for the age of regions (``min-age`` and ``max-age``), and a
+predefined integer for memory management actions should be used.  The supported
+numbers and their meanings are as below.
+
+ - 0: Call ``madvise()`` for the region with ``MADV_WILLNEED``
+ - 1: Call ``madvise()`` for the region with ``MADV_COLD``
+ - 2: Call ``madvise()`` for the region with ``MADV_PAGEOUT``
+ - 3: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``
+ - 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
+ - 5: Do nothing but count the statistics
+
+You can disable schemes by simply writing an empty string to the file.  For
+example, below commands applies a scheme saying "If a memory region of size in
+[4KiB, 8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
+interval in [10, 20], page out the region", check the entered scheme again, and
+finally remove the scheme. ::
+
+    # cd <debugfs>/damon
+    # echo "4096 8192    0 5    10 20    2" > schemes
+    # cat schemes
+    4096 8192 0 5 10 20 2 0 0
+    # echo > schemes
+
+The last two integers in the 4th line of above example is the total number and
+the total size of the regions that the scheme is applied.
+
+
 Turning On/Off
 --------------
 
-- 
2.17.1