[PATCH 00/15] Introduce DAMON-based Proactive Reclamation

[PATCH 00/15] Introduce DAMON-based Proactive Reclamation

[SeongJae Park]

Changes from Previous Version (RFC v3)
======================================

Compared to the RFC v3
(https://lore.kernel.org/linux-mm/20210720131309.22073-1-sj38.park@gmail.com/),
this version contains below changes.

- Rebase on latest -mm tree
- Use less aggressive default parameter values (coldness threshold: 5s ->
  2mins, cpu time quota: 100ms/1s -> 10ms/1s, size quota: 1GiB/s -> 128MiB/s)
- Update the evaluation results in the coverletter

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

This patchset 1) makes the engine for general data access pattern-oriented
memory management (DAMOS) be more useful for production environments, and
2) implements a static kernel module for lightweight proactive reclamation
using the engine.

Proactive Reclamation
---------------------

On general memory over-committed systems, proactively reclaiming cold pages
helps saving memory and reducing latency spikes that incurred by the direct
reclaim or the CPU consumption of kswapd, while incurring only minimal
performance degradation[2].

A Free Pages Reporting[8] based memory over-commit virtualization system would
be one more specific use case.  In the system, the guest VMs reports their free
memory to host, and the host reallocates the reported memory to other guests.
As a result, the system's memory utilization can be maximized.  However, the
guests could be not so memory-frugal, because some kernel subsystems and
user-space applications are designed to use as much memory as available.  Then,
guests would report only small amount of free memory to host, results in poor
memory utilization.  Running the proactive reclamation in such guests could
help mitigating this problem.

Google has also implemented this idea and using it in their data center.  They
further proposed upstreaming it in LSFMM'19, and "the general consensus was
that, while this sort of proactive reclaim would be useful for a number of
users, the cost of this particular solution was too high to consider merging it
upstream"[3].  The cost mainly comes from the coldness tracking.  Roughly
speaking, the implementation periodically scans the 'Accessed' bit of each
page.  For the reason, the overhead linearly increases as the size of the
memory and the scanning frequency grows.  As a result, Google is known to
dedicating one CPU for the work.  That's a reasonable option to someone like
Google, but it wouldn't be so to some others.

DAMON and DAMOS: An engine for data access pattern-oriented memory management
-----------------------------------------------------------------------------

DAMON[4] is a framework for general data access monitoring.  Its adaptive
monitoring overhead control feature minimizes its monitoring overhead.  It also
let the upper-bound of the overhead be configurable by clients, regardless of
the size of the monitoring target memory.  While monitoring 70 GiB memory of a
production system every 5 milliseconds, it consumes less than 1% single CPU
time.  For this, it could sacrify some of the quality of the monitoring
results.  Nevertheless, the lower-bound of the quality is configurable, and it
uses a best-effort algorithm for better quality.  Our test results[5] show the
quality is practical enough.  From the production system monitoring, we were
able to find a 4 KiB region in the 70 GiB memory that shows highest access
frequency.

We normally don't monitor the data access pattern just for fun but to improve
something like memory management.  Proactive reclamation is one such usage.
For such general cases, DAMON provides a feature called DAMon-based Operation
Schemes (DAMOS)[6].  It makes DAMON an engine for general data access pattern
oriented memory management.  Using this, clients can ask DAMON to find memory
regions of specific data access pattern and apply some memory management action
(e.g., page out, move to head of the LRU list, use huge page, ...).  We call
the request 'scheme'.

Proactive Reclamation on top of DAMON/DAMOS
-------------------------------------------

Therefore, by using DAMON for the cold pages detection, the proactive
reclamation's monitoring overhead issue can be solved.  Actually, we previously
implemented a version of proactive reclamation using DAMOS and achieved
noticeable improvements with our evaluation setup[5].  Nevertheless, it more
for a proof-of-concept, rather than production uses.  It supports only virtual
address spaces of processes, and require additional tuning efforts for given
workloads and the hardware.  For the tuning, we introduced a simple auto-tuning
user space tool[8].  Google is also known to using a ML-based similar approach
for their fleets[2].  But, making it just works with intuitive knobs in the
kernel would be helpful for general users.

To this end, this patchset improves DAMOS to be ready for such production
usages, and implements another version of the proactive reclamation, namely
DAMON_RECLAIM, on top of it.

DAMOS Improvements: Aggressiveness Control, Prioritization, and Watermarks
--------------------------------------------------------------------------

First of all, the current version of DAMOS supports only virtual address
spaces.  This patchset makes it supports the physical address space for the
page out action.

Next major problem of the current version of DAMOS is the lack of the
aggressiveness control, which can results in arbitrary overhead.  For example,
if huge memory regions having the data access pattern of interest are found,
applying the requested action to all of the regions could incur significant
overhead.  It can be controlled by tuning the target data access pattern with
manual or automated approaches[2,7].  But, some people would prefer the kernel
to just work with only intuitive tuning or default values.

For such cases, this patchset implements a safeguard, namely time/size quota.
Using this, the clients can specify up to how much time can be used for
applying the action, and/or up to how much memory regions the action can be
applied within a user-specified time duration.  A followup question is, to
which memory regions should the action applied within the limits?  We implement
a simple regions prioritization mechanism for each action and make DAMOS to
apply the action to high priority regions first.  It also allows clients tune
the prioritization mechanism to use different weights for size, access
frequency, and age of memory regions.  This means we could use not only LRU but
also LFU or some fancy algorithms like CAR[9] with lightweight overhead.

Though DAMON is lightweight, someone would want to remove even the cold pages
monitoring overhead when it is unnecessary.  Currently, it should manually
turned on and off by clients, but some clients would simply want to turn it on
and off based on some metrics like free memory ratio or memory fragmentation.
For such cases, this patchset implements a watermarks-based automatic
activation feature.  It allows the clients configure the metric of their
interest, and three watermarks of the metric.  If the metric is higher than the
high watermark or lower than the low watermark, the scheme is deactivated.  If
the metric is lower than the mid watermark but higher than the low watermark,
the scheme is activated.

DAMON-based Reclaim
-------------------

Using the improved version of DAMOS, this patchset implements a static kernel
module called 'damon_reclaim'.  It finds memory regions that didn't accessed
for specific time duration and page out.  Consuming too much CPU for the paging
out operations, or doing pageout too frequently can be critical for systems
configuring their swap devices with software-defined in-memory block devices
like zram/zswap or total number of writes limited devices like SSDs,
respectively.  To avoid the problems, the time/size quotas can be configured.
Under the quotas, it pages out memory regions that didn't accessed longer
first.  Also, to remove the monitoring overhead under peaceful situation, and
to fall back to the LRU-list based page granularity reclamation when it doesn't
make progress, the three watermarks based activation mechanism is used, with
the free memory ratio as the watermark metric.

For convenient configurations, it provides several module parameters.  Using
these, sysadmins can enable/disable it, and tune its parameters including the
coldness identification time threshold, the time/size quotas and the three
watermarks.

Evaluation
==========

In short, DAMON_RECLAIM with 50ms/s time quota and regions prioritization on
v5.15-rc5 Linux kernel with ZRAM swap device achieves 38.58% memory saving with
only 1.94% runtime overhead.  For this, DAMON_RECLAIM consumes only 4.97% of
single CPU time.

Setup
-----

We evaluate DAMON_RECLAIM to show how each of the DAMOS improvements make
effect.  For this, we measure DAMON_RECLAIM's CPU consumption, entire system
memory footprint, total number of major page faults, and runtime of 24
realistic workloads in PARSEC3 and SPLASH-2X benchmark suites on my QEMU/KVM
based virtual machine.  The virtual machine runs on an i3.metal AWS instance,
has 130GiB memory, and runs a linux kernel built on latest -mm tree[1] plus
this patchset.  It also utilizes a 4 GiB ZRAM swap device.  We repeats the
measurement 5 times and use averages.

[1] https://github.com/hnaz/linux-mm/tree/v5.15-rc5-mmots-2021-10-13-19-55

Detailed Results
----------------

The results are summarized in the below table.

With coldness identification threshold of 5 seconds, DAMON_RECLAIM without the
time quota-based speed limit achieves 47.21% memory saving, but incur 4.59%
runtime slowdown to the workloads on average.  For this, DAMON_RECLAIM consumes
about 11.28% single CPU time.

Applying time quotas of 200ms/s, 50ms/s, and 10ms/s without the regions
prioritization reduces the slowdown to 4.89%, 2.65%, and 1.5%, respectively.
Time quota of 200ms/s (20%) makes no real change compared to the quota
unapplied version, because the quota unapplied version consumes only 11.28% CPU
time.  DAMON_RECLAIM's CPU utilization also similarly reduced: 11.24%, 5.51%,
and 2.01% of single CPU time.  That is, the overhead is proportional to the
speed limit.  Nevertheless, it also reduces the memory saving because it
becomes less aggressive.  In detail, the three variants show 48.76%, 37.83%,
and 7.85% memory saving, respectively.

Applying the regions prioritization (page out regions that not accessed longer
first within the time quota) further reduces the performance degradation.
Runtime slowdowns and total number of major page faults increase has been
4.89%/218,690% -> 4.39%/166,136% (200ms/s), 2.65%/111,886% -> 1.94%/59,053%
(50ms/s), and 1.5%/34,973.40% -> 2.08%/8,781.75% (10ms/s).  The runtime under
10ms/s time quota has increased with prioritization, but apparently that's
under the margin of error.

    time quota   prioritization  memory_saving  cpu_util  slowdown  pgmajfaults overhead
    N            N               47.21%         11.28%    4.59%     194,802%
    200ms/s      N               48.76%         11.24%    4.89%     218,690%
    50ms/s       N               37.83%         5.51%     2.65%     111,886%
    10ms/s       N               7.85%          2.01%     1.5%      34,793.40%
    200ms/s      Y               50.08%         10.38%    4.39%     166,136%
    50ms/s       Y               38.58%         4.97%     1.94%     59,053%
    10ms/s       Y               3.63%          1.73%     2.08%     8,781.75%

Baseline and Complete Git Trees
===============================

The patches are based on the latest -mm tree
(v5.15-rc5-mmots-2021-10-13-19-55).  You can also clone the complete git tree
from:

    $ git clone git://github.com/sjp38/linux -b damon_reclaim/patches/v1

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

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

The first patch makes DAMOS support the physical address space for the page out
action.  Following five patches (patches 2-6) implement the time/size quotas.
Next four patches (patches 7-10) implement the memory regions prioritization
within the limit.  Then, three following patches (patches 11-13) implement the
watermarks-based schemes activation.  Finally, the last two patches (patches
14-15) implement and document the DAMON-based reclamation using the advanced
DAMOS.

[1] https://www.kernel.org/doc/html/v5.15-rc1/vm/damon/index.html
[2] https://research.google/pubs/pub48551/
[3] https://lwn.net/Articles/787611/
[4] https://damonitor.github.io
[5] https://damonitor.github.io/doc/html/latest/vm/damon/eval.html
[6] https://lore.kernel.org/linux-mm/20211001125604.29660-1-sj@kernel.org/
[7] https://github.com/awslabs/damoos
[8] https://www.kernel.org/doc/html/latest/vm/free_page_reporting.html
[9] https://www.usenix.org/conference/fast-04/car-clock-adaptive-replacement

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

Changes from RFC v3
(https://lore.kernel.org/linux-mm/20210720131309.22073-1-sj38.park@gmail.com/)
- Rebase on latest -mm tree
- Use less aggressive default parameter values (coldness threshold: 5s ->
  2mins, cpu time quota: 100ms/1s -> 10ms/1s, size quota: 1GiB/s -> 128MiB/s)
- Update the evaluation results in the coverletter

Changes from RFC v2
(https://lore.kernel.org/linux-mm/20210608115254.11930-1-sj38.park@gmail.com/)
- Rebase on latest -mm tree (v5.14-rc1-mmots-2021-07-15-18-47)
- Make reclamation restarts from exactly the point it stopped due to the limit
- Implement a time quota (limits the time for trying reclamation of cold pages)

[1] https://lore.kernel.org/linux-mm/20210716081449.22187-1-sj38.park@gmail.com/

Changes from RFC v1
(https://lore.kernel.org/linux-mm/20210531133816.12689-1-sj38.park@gmail.com/)
- Avoid fake I/O load reporting (James Gowans)
- Remove kernel configs for the build time enabling and the parameters setting
- Export kdamond pid via a readonly parameter file
- Elaborate coverletter, especially for evaluation and DAMON_RECLAIM interface
- Add documentation
- Rebase on -mm tree
- Cleanup code

SeongJae Park (15):
  mm/damon/paddr: Support the pageout scheme
  mm/damon/schemes: Implement size quota for schemes application speed
    control
  mm/damon/schemes: Skip already charged targets and regions
  mm/damon/schemes: Implement time quota
  mm/damon/dbgfs: Support quotas of schemes
  mm/damon/selftests: Support schemes quotas
  mm/damon/schemes: Prioritize regions within the quotas
  mm/damon/vaddr,paddr: Support pageout prioritization
  mm/damon/dbgfs: Support prioritization weights
  tools/selftests/damon: Update for regions prioritization of schemes
  mm/damon/schemes: Activate schemes based on a watermarks mechanism
  mm/damon/dbgfs: Support watermarks
  selftests/damon: Support watermarks
  mm/damon: Introduce DAMON-based Reclamation (DAMON_RECLAIM)
  Documentation/admin-guide/mm/damon: Add a document for DAMON_RECLAIM

 Documentation/admin-guide/mm/damon/index.rst  |   1 +
 .../admin-guide/mm/damon/reclaim.rst          | 235 ++++++++++++
 include/linux/damon.h                         | 136 ++++++-
 mm/damon/Kconfig                              |  12 +
 mm/damon/Makefile                             |   1 +
 mm/damon/core.c                               | 283 +++++++++++++-
 mm/damon/dbgfs.c                              |  29 +-
 mm/damon/paddr.c                              |  51 ++-
 mm/damon/prmtv-common.c                       |  46 +++
 mm/damon/prmtv-common.h                       |   3 +
 mm/damon/reclaim.c                            | 354 ++++++++++++++++++
 mm/damon/vaddr.c                              |  15 +
 .../testing/selftests/damon/debugfs_attrs.sh  |   4 +-
 13 files changed, 1145 insertions(+), 25 deletions(-)
 create mode 100644 Documentation/admin-guide/mm/damon/reclaim.rst
 create mode 100644 mm/damon/reclaim.c

-- 
2.17.1

[PATCH 01/15] mm/damon/paddr: Support the pageout scheme

[SeongJae Park]

This commit makes the DAMON primitives for physical address space
support the pageout action for DAMON-based Operation Schemes.  With this
commit, hence, users can easily implement system-level data access-aware
reclamations using DAMOS.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/paddr.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index d7a2ecd09ed0..957ada55de77 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -11,7 +11,9 @@
 #include <linux/page_idle.h>
 #include <linux/pagemap.h>
 #include <linux/rmap.h>
+#include <linux/swap.h>
 
+#include "../internal.h"
 #include "prmtv-common.h"
 
 static bool __damon_pa_mkold(struct page *page, struct vm_area_struct *vma,
@@ -211,6 +213,39 @@ bool damon_pa_target_valid(void *t)
 	return true;
 }
 
+int damon_pa_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme)
+{
+	unsigned long addr;
+	LIST_HEAD(page_list);
+
+	if (scheme->action != DAMOS_PAGEOUT)
+		return -EINVAL;
+
+	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
+		struct page *page = damon_get_page(PHYS_PFN(addr));
+
+		if (!page)
+			continue;
+
+		ClearPageReferenced(page);
+		test_and_clear_page_young(page);
+		if (isolate_lru_page(page)) {
+			put_page(page);
+			continue;
+		}
+		if (PageUnevictable(page)) {
+			putback_lru_page(page);
+		} else {
+			list_add(&page->lru, &page_list);
+			put_page(page);
+		}
+	}
+	reclaim_pages(&page_list);
+	cond_resched();
+	return 0;
+}
+
 void damon_pa_set_primitives(struct damon_ctx *ctx)
 {
 	ctx->primitive.init = NULL;
@@ -220,5 +255,5 @@ void damon_pa_set_primitives(struct damon_ctx *ctx)
 	ctx->primitive.reset_aggregated = NULL;
 	ctx->primitive.target_valid = damon_pa_target_valid;
 	ctx->primitive.cleanup = NULL;
-	ctx->primitive.apply_scheme = NULL;
+	ctx->primitive.apply_scheme = damon_pa_apply_scheme;
 }
-- 
2.17.1

[PATCH 02/15] mm/damon/schemes: Implement size quota for schemes application speed control

[SeongJae Park]

There could be arbitrarily large memory regions fulfilling the target
data access pattern of a DAMON-based operation scheme.  In the case,
applying the action of the scheme could incur too high overhead.  To
provide an intuitive way for avoiding it, this commit implements a
feature called size quota.  If the quota is set, DAMON tries to apply
the action only up to the given amount of memory regions within a given
time window.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 36 +++++++++++++++++++++++---
 mm/damon/core.c       | 60 +++++++++++++++++++++++++++++++++++++------
 mm/damon/dbgfs.c      |  4 ++-
 3 files changed, 87 insertions(+), 13 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 715dadd21f7c..af8c2ada2655 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -89,6 +89,26 @@ enum damos_action {
 	DAMOS_STAT,		/* Do nothing but only record the stat */
 };
 
+/**
+ * struct damos_quota - Controls the aggressiveness of the given scheme.
+ * @sz:			Maximum bytes of memory that the action can be applied.
+ * @reset_interval:	Charge reset interval in milliseconds.
+ *
+ * To avoid consuming too much CPU time or IO resources for applying the
+ * &struct damos->action to large memory, DAMON allows users to set a size
+ * quota.  The quota can be set by writing non-zero values to &sz.  If the size
+ * quota is set, DAMON tries to apply the action only up to &sz bytes within
+ * &reset_interval.
+ */
+struct damos_quota {
+	unsigned long sz;
+	unsigned long reset_interval;
+
+/* private: For charging the quota */
+	unsigned long charged_sz;
+	unsigned long charged_from;
+};
+
 /**
  * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
  * @min_sz_region:	Minimum size of target regions.
@@ -98,13 +118,20 @@ 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.
+ * @quota:		Control the aggressiveness of this scheme.
  * @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.
  *
- * 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.
+ * For each aggregation interval, DAMON finds regions which fit in the
+ * condition (&min_sz_region, &max_sz_region, &min_nr_accesses,
+ * &max_nr_accesses, &min_age_region, &max_age_region) and applies &action to
+ * those.  To avoid consuming too much CPU time or IO resources for the
+ * &action, &quota is used.
+ *
+ * After applying the &action to each region, &stat_count and &stat_sz is
+ * updated to reflect the number of regions and total size of regions that the
+ * &action is applied.
  */
 struct damos {
 	unsigned long min_sz_region;
@@ -114,6 +141,7 @@ struct damos {
 	unsigned int min_age_region;
 	unsigned int max_age_region;
 	enum damos_action action;
+	struct damos_quota quota;
 	unsigned long stat_count;
 	unsigned long stat_sz;
 	struct list_head list;
@@ -310,7 +338,7 @@ 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);
+		enum damos_action action, struct damos_quota *quota);
 void damon_add_scheme(struct damon_ctx *ctx, struct damos *s);
 void damon_destroy_scheme(struct damos *s);
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 2f6785737902..cce14a0d5c72 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -89,7 +89,7 @@ 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)
+		enum damos_action action, struct damos_quota *quota)
 {
 	struct damos *scheme;
 
@@ -107,6 +107,11 @@ struct damos *damon_new_scheme(
 	scheme->stat_sz = 0;
 	INIT_LIST_HEAD(&scheme->list);
 
+	scheme->quota.sz = quota->sz;
+	scheme->quota.reset_interval = quota->reset_interval;
+	scheme->quota.charged_sz = 0;
+	scheme->quota.charged_from = 0;
+
 	return scheme;
 }
 
@@ -530,15 +535,25 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
 	}
 }
 
+static void damon_split_region_at(struct damon_ctx *ctx,
+		struct damon_target *t, struct damon_region *r,
+		unsigned long sz_r);
+
 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;
+		struct damos_quota *quota = &s->quota;
+		unsigned long sz = r->ar.end - r->ar.start;
+
+		/* Check the quota */
+		if (quota->sz && quota->charged_sz >= quota->sz)
+			continue;
+
+		/* Check the target regions condition */
 		if (sz < s->min_sz_region || s->max_sz_region < sz)
 			continue;
 		if (r->nr_accesses < s->min_nr_accesses ||
@@ -546,22 +561,51 @@ 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)
+
+		/* Apply the scheme */
+		if (c->primitive.apply_scheme) {
+			if (quota->sz && quota->charged_sz + sz > quota->sz) {
+				sz = ALIGN_DOWN(quota->sz - quota->charged_sz,
+						DAMON_MIN_REGION);
+				if (!sz)
+					goto update_stat;
+				damon_split_region_at(c, t, r, sz);
+			}
 			c->primitive.apply_scheme(c, t, r, s);
+			quota->charged_sz += sz;
+		}
 		if (s->action != DAMOS_STAT)
 			r->age = 0;
+
+update_stat:
+		s->stat_count++;
+		s->stat_sz += sz;
 	}
 }
 
 static void kdamond_apply_schemes(struct damon_ctx *c)
 {
 	struct damon_target *t;
-	struct damon_region *r;
+	struct damon_region *r, *next_r;
+	struct damos *s;
+
+	damon_for_each_scheme(s, c) {
+		struct damos_quota *quota = &s->quota;
+
+		if (!quota->sz)
+			continue;
+
+		/* New charge window starts */
+		if (time_after_eq(jiffies, quota->charged_from +
+					msecs_to_jiffies(
+						quota->reset_interval))) {
+			quota->charged_from = jiffies;
+			quota->charged_sz = 0;
+		}
+	}
 
 	damon_for_each_target(t, c) {
-		damon_for_each_region(r, t)
+		damon_for_each_region_safe(r, next_r, t)
 			damon_do_apply_schemes(c, t, r);
 	}
 }
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index c90988a20fa4..a04bd50cc4c4 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -188,6 +188,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 
 	*nr_schemes = 0;
 	while (pos < len && *nr_schemes < max_nr_schemes) {
+		struct damos_quota quota = {};
+
 		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);
@@ -200,7 +202,7 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 
 		pos += parsed;
 		scheme = damon_new_scheme(min_sz, max_sz, min_nr_a, max_nr_a,
-				min_age, max_age, action);
+				min_age, max_age, action, &quota);
 		if (!scheme)
 			goto fail;
 
-- 
2.17.1

[PATCH 03/15] mm/damon/schemes: Skip already charged targets and regions

[SeongJae Park]

If DAMOS has stopped applying action in the middle of a group of memory
regions due to its size quota, it starts the work again from the
beginning of the address space in the next charge window.  If there is a
huge memory region at the beginning of the address space and it fulfills
the scheme's target data access pattern always, the action will applied
to only the region.

This commit mitigates the case by skipping memory regions that charged
in current charge window at the beginning of next charge window.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  5 +++++
 mm/damon/core.c       | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index af8c2ada2655..1fec32e18319 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -107,6 +107,8 @@ struct damos_quota {
 /* private: For charging the quota */
 	unsigned long charged_sz;
 	unsigned long charged_from;
+	struct damon_target *charge_target_from;
+	unsigned long charge_addr_from;
 };
 
 /**
@@ -307,6 +309,9 @@ struct damon_ctx {
 #define damon_prev_region(r) \
 	(container_of(r->list.prev, struct damon_region, list))
 
+#define damon_last_region(t) \
+	(list_last_entry(&t->regions_list, struct damon_region, list))
+
 #define damon_for_each_region(r, t) \
 	list_for_each_entry(r, &t->regions_list, list)
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index cce14a0d5c72..693b75bc3450 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -111,6 +111,8 @@ struct damos *damon_new_scheme(
 	scheme->quota.reset_interval = quota->reset_interval;
 	scheme->quota.charged_sz = 0;
 	scheme->quota.charged_from = 0;
+	scheme->quota.charge_target_from = NULL;
+	scheme->quota.charge_addr_from = 0;
 
 	return scheme;
 }
@@ -553,6 +555,37 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		if (quota->sz && quota->charged_sz >= quota->sz)
 			continue;
 
+		/* Skip previously charged regions */
+		if (quota->charge_target_from) {
+			if (t != quota->charge_target_from)
+				continue;
+			if (r == damon_last_region(t)) {
+				quota->charge_target_from = NULL;
+				quota->charge_addr_from = 0;
+				continue;
+			}
+			if (quota->charge_addr_from &&
+					r->ar.end <= quota->charge_addr_from)
+				continue;
+
+			if (quota->charge_addr_from && r->ar.start <
+					quota->charge_addr_from) {
+				sz = ALIGN_DOWN(quota->charge_addr_from -
+						r->ar.start, DAMON_MIN_REGION);
+				if (!sz) {
+					if (r->ar.end - r->ar.start <=
+							DAMON_MIN_REGION)
+						continue;
+					sz = DAMON_MIN_REGION;
+				}
+				damon_split_region_at(c, t, r, sz);
+				r = damon_next_region(r);
+				sz = r->ar.end - r->ar.start;
+			}
+			quota->charge_target_from = NULL;
+			quota->charge_addr_from = 0;
+		}
+
 		/* Check the target regions condition */
 		if (sz < s->min_sz_region || s->max_sz_region < sz)
 			continue;
@@ -573,6 +606,10 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			}
 			c->primitive.apply_scheme(c, t, r, s);
 			quota->charged_sz += sz;
+			if (quota->sz && quota->charged_sz >= quota->sz) {
+				quota->charge_target_from = t;
+				quota->charge_addr_from = r->ar.end + 1;
+			}
 		}
 		if (s->action != DAMOS_STAT)
 			r->age = 0;
-- 
2.17.1

[PATCH 04/15] mm/damon/schemes: Implement time quota

[SeongJae Park]

The size quota feature of DAMOS is useful for IO resource-critical
systems, but not so intuitive for CPU time-critical systems.  Systems
using zram or zswap-like swap device would be examples.

To provide another intuitive ways for such systems, this commit
implements time-based quota for DAMON-based Operation Schemes.  If the
quota is set, DAMOS tries to use only up to the user-defined quota of
CPU time within a given time window.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 25 +++++++++++++++++++-----
 mm/damon/core.c       | 45 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 1fec32e18319..5347f940818e 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -91,20 +91,35 @@ enum damos_action {
 
 /**
  * struct damos_quota - Controls the aggressiveness of the given scheme.
+ * @ms:			Maximum milliseconds that the scheme can use.
  * @sz:			Maximum bytes of memory that the action can be applied.
  * @reset_interval:	Charge reset interval in milliseconds.
  *
  * To avoid consuming too much CPU time or IO resources for applying the
- * &struct damos->action to large memory, DAMON allows users to set a size
- * quota.  The quota can be set by writing non-zero values to &sz.  If the size
- * quota is set, DAMON tries to apply the action only up to &sz bytes within
- * &reset_interval.
+ * &struct damos->action to large memory, DAMON allows users to set time and/or
+ * size quotas.  The quotas can be set by writing non-zero values to &ms and
+ * &sz, respectively.  If the time quota is set, DAMON tries to use only up to
+ * &ms milliseconds within &reset_interval for applying the action.  If the
+ * size quota is set, DAMON tries to apply the action only up to &sz bytes
+ * within &reset_interval.
+ *
+ * Internally, the time quota is transformed to a size quota using estimated
+ * throughput of the scheme's action.  DAMON then compares it against &sz and
+ * uses smaller one as the effective quota.
  */
 struct damos_quota {
+	unsigned long ms;
 	unsigned long sz;
 	unsigned long reset_interval;
 
-/* private: For charging the quota */
+/* private: */
+	/* For throughput estimation */
+	unsigned long total_charged_sz;
+	unsigned long total_charged_ns;
+
+	unsigned long esz;	/* Effective size quota in bytes */
+
+	/* For charging the quota */
 	unsigned long charged_sz;
 	unsigned long charged_from;
 	struct damon_target *charge_target_from;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 693b75bc3450..d1da4bef96ed 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -107,8 +107,12 @@ struct damos *damon_new_scheme(
 	scheme->stat_sz = 0;
 	INIT_LIST_HEAD(&scheme->list);
 
+	scheme->quota.ms = quota->ms;
 	scheme->quota.sz = quota->sz;
 	scheme->quota.reset_interval = quota->reset_interval;
+	scheme->quota.total_charged_sz = 0;
+	scheme->quota.total_charged_ns = 0;
+	scheme->quota.esz = 0;
 	scheme->quota.charged_sz = 0;
 	scheme->quota.charged_from = 0;
 	scheme->quota.charge_target_from = NULL;
@@ -550,9 +554,10 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 	damon_for_each_scheme(s, c) {
 		struct damos_quota *quota = &s->quota;
 		unsigned long sz = r->ar.end - r->ar.start;
+		struct timespec64 begin, end;
 
 		/* Check the quota */
-		if (quota->sz && quota->charged_sz >= quota->sz)
+		if (quota->esz && quota->charged_sz >= quota->esz)
 			continue;
 
 		/* Skip previously charged regions */
@@ -597,16 +602,21 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 
 		/* Apply the scheme */
 		if (c->primitive.apply_scheme) {
-			if (quota->sz && quota->charged_sz + sz > quota->sz) {
-				sz = ALIGN_DOWN(quota->sz - quota->charged_sz,
+			if (quota->esz &&
+					quota->charged_sz + sz > quota->esz) {
+				sz = ALIGN_DOWN(quota->esz - quota->charged_sz,
 						DAMON_MIN_REGION);
 				if (!sz)
 					goto update_stat;
 				damon_split_region_at(c, t, r, sz);
 			}
+			ktime_get_coarse_ts64(&begin);
 			c->primitive.apply_scheme(c, t, r, s);
+			ktime_get_coarse_ts64(&end);
+			quota->total_charged_ns += timespec64_to_ns(&end) -
+				timespec64_to_ns(&begin);
 			quota->charged_sz += sz;
-			if (quota->sz && quota->charged_sz >= quota->sz) {
+			if (quota->esz && quota->charged_sz >= quota->esz) {
 				quota->charge_target_from = t;
 				quota->charge_addr_from = r->ar.end + 1;
 			}
@@ -620,6 +630,29 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 	}
 }
 
+/* Shouldn't be called if quota->ms and quota->sz are zero */
+static void damos_set_effective_quota(struct damos_quota *quota)
+{
+	unsigned long throughput;
+	unsigned long esz;
+
+	if (!quota->ms) {
+		quota->esz = quota->sz;
+		return;
+	}
+
+	if (quota->total_charged_ns)
+		throughput = quota->total_charged_sz * 1000000 /
+			quota->total_charged_ns;
+	else
+		throughput = PAGE_SIZE * 1024;
+	esz = throughput * quota->ms;
+
+	if (quota->sz && quota->sz < esz)
+		esz = quota->sz;
+	quota->esz = esz;
+}
+
 static void kdamond_apply_schemes(struct damon_ctx *c)
 {
 	struct damon_target *t;
@@ -629,15 +662,17 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 	damon_for_each_scheme(s, c) {
 		struct damos_quota *quota = &s->quota;
 
-		if (!quota->sz)
+		if (!quota->ms && !quota->sz)
 			continue;
 
 		/* New charge window starts */
 		if (time_after_eq(jiffies, quota->charged_from +
 					msecs_to_jiffies(
 						quota->reset_interval))) {
+			quota->total_charged_sz += quota->charged_sz;
 			quota->charged_from = jiffies;
 			quota->charged_sz = 0;
+			damos_set_effective_quota(quota);
 		}
 	}
 
-- 
2.17.1

[PATCH 05/15] mm/damon/dbgfs: Support quotas of schemes

[SeongJae Park]

This commit makes the debugfs interface of DAMON support the scheme
quotas by chaning the format of the input for the schemes file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index a04bd50cc4c4..097e6745ba75 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -105,11 +105,14 @@ 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 %lu %lu\n",
+				"%lu %lu %u %u %u %u %d %lu %lu %lu %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->stat_count, s->stat_sz);
+				s->action,
+				s->quota.ms, s->quota.sz,
+				s->quota.reset_interval,
+				s->stat_count, s->stat_sz);
 		if (!rc)
 			return -ENOMEM;
 
@@ -190,10 +193,11 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 	while (pos < len && *nr_schemes < max_nr_schemes) {
 		struct damos_quota quota = {};
 
-		ret = sscanf(&str[pos], "%lu %lu %u %u %u %u %u%n",
+		ret = sscanf(&str[pos], "%lu %lu %u %u %u %u %u %lu %lu %lu%n",
 				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
-				&min_age, &max_age, &action, &parsed);
-		if (ret != 7)
+				&min_age, &max_age, &action, &quota.ms,
+				&quota.sz, &quota.reset_interval, &parsed);
+		if (ret != 10)
 			break;
 		if (!damos_action_valid(action)) {
 			pr_err("wrong action %d\n", action);
-- 
2.17.1

[PATCH 06/15] mm/damon/selftests: Support schemes quotas

[SeongJae Park]

This commit updates DAMON selftests to support updated schemes debugfs
file format for the quotas.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/debugfs_attrs.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/damon/debugfs_attrs.sh b/tools/testing/selftests/damon/debugfs_attrs.sh
index 639cfb6a1f65..8e33a7b584e7 100755
--- a/tools/testing/selftests/damon/debugfs_attrs.sh
+++ b/tools/testing/selftests/damon/debugfs_attrs.sh
@@ -63,10 +63,10 @@ echo "$orig_content" > "$file"
 file="$DBGFS/schemes"
 orig_content=$(cat "$file")
 
-test_write_succ "$file" "1 2 3 4 5 6 4" \
+test_write_succ "$file" "1 2 3 4 5 6 4 0 0 0" \
 	"$orig_content" "valid input"
 test_write_fail "$file" "1 2
-3 4 5 6 3" "$orig_content" "multi lines"
+3 4 5 6 3 0 0 0" "$orig_content" "multi lines"
 test_write_succ "$file" "" "$orig_content" "disabling"
 echo "$orig_content" > "$file"
 
-- 
2.17.1

[PATCH 07/15] mm/damon/schemes: Prioritize regions within the quotas

[SeongJae Park]

This commit makes DAMON apply schemes to regions having higher priority
first, if it cannot apply schemes to all regions due to the quotas.

The prioritization function should be implemented in the monitoring
primitives.  Those would commonly calculate the priority of the region
using attributes of regions, namely 'size', 'nr_accesses', and 'age'.
For example, some primitive would calculate the priority of each region
using a weighted sum of 'nr_accesses' and 'age' of the region.

The optimal weights would depend on give environments, so this commit
makes those customizable.  Nevertheless, the score calculation functions
are only encouraged to respect the weights, not mandated.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 26 ++++++++++++++++++
 mm/damon/core.c       | 62 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 81 insertions(+), 7 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 5347f940818e..999918a07444 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -14,6 +14,8 @@
 
 /* Minimal region size.  Every damon_region is aligned by this. */
 #define DAMON_MIN_REGION	PAGE_SIZE
+/* Max priority score for DAMON-based operation schemes */
+#define DAMOS_MAX_SCORE		(99)
 
 /**
  * struct damon_addr_range - Represents an address region of [@start, @end).
@@ -95,6 +97,10 @@ enum damos_action {
  * @sz:			Maximum bytes of memory that the action can be applied.
  * @reset_interval:	Charge reset interval in milliseconds.
  *
+ * @weight_sz:		Weight of the region's size for prioritization.
+ * @weight_nr_accesses:	Weight of the region's nr_accesses for prioritization.
+ * @weight_age:		Weight of the region's age for prioritization.
+ *
  * To avoid consuming too much CPU time or IO resources for applying the
  * &struct damos->action to large memory, DAMON allows users to set time and/or
  * size quotas.  The quotas can be set by writing non-zero values to &ms and
@@ -106,12 +112,22 @@ enum damos_action {
  * Internally, the time quota is transformed to a size quota using estimated
  * throughput of the scheme's action.  DAMON then compares it against &sz and
  * uses smaller one as the effective quota.
+ *
+ * For selecting regions within the quota, DAMON prioritizes current scheme's
+ * target memory regions using the &struct damon_primitive->get_scheme_score.
+ * You could customize the prioritization logic by setting &weight_sz,
+ * &weight_nr_accesses, and &weight_age, because monitoring primitives are
+ * encouraged to respect those.
  */
 struct damos_quota {
 	unsigned long ms;
 	unsigned long sz;
 	unsigned long reset_interval;
 
+	unsigned int weight_sz;
+	unsigned int weight_nr_accesses;
+	unsigned int weight_age;
+
 /* private: */
 	/* For throughput estimation */
 	unsigned long total_charged_sz;
@@ -124,6 +140,10 @@ struct damos_quota {
 	unsigned long charged_from;
 	struct damon_target *charge_target_from;
 	unsigned long charge_addr_from;
+
+	/* For prioritization */
+	unsigned long histogram[DAMOS_MAX_SCORE + 1];
+	unsigned int min_score;
 };
 
 /**
@@ -174,6 +194,7 @@ 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.
+ * @get_scheme_score:		Get the score of a region for a scheme.
  * @apply_scheme:		Apply a DAMON-based operation scheme.
  * @target_valid:		Determine if the target is valid.
  * @cleanup:			Clean up the context.
@@ -200,6 +221,8 @@ 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.
+ * @get_scheme_score should return the priority score of a region for a scheme
+ * as an integer in [0, &DAMOS_MAX_SCORE].
  * @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.
@@ -213,6 +236,9 @@ 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 (*get_scheme_score)(struct damon_ctx *context,
+			struct damon_target *t, struct damon_region *r,
+			struct damos *scheme);
 	int (*apply_scheme)(struct damon_ctx *context, struct damon_target *t,
 			struct damon_region *r, struct damos *scheme);
 	bool (*target_valid)(void *target);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index d1da4bef96ed..fad25778e2ec 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -12,6 +12,7 @@
 #include <linux/kthread.h>
 #include <linux/random.h>
 #include <linux/slab.h>
+#include <linux/string.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/damon.h>
@@ -110,6 +111,9 @@ struct damos *damon_new_scheme(
 	scheme->quota.ms = quota->ms;
 	scheme->quota.sz = quota->sz;
 	scheme->quota.reset_interval = quota->reset_interval;
+	scheme->quota.weight_sz = quota->weight_sz;
+	scheme->quota.weight_nr_accesses = quota->weight_nr_accesses;
+	scheme->quota.weight_age = quota->weight_age;
 	scheme->quota.total_charged_sz = 0;
 	scheme->quota.total_charged_ns = 0;
 	scheme->quota.esz = 0;
@@ -545,6 +549,28 @@ static void damon_split_region_at(struct damon_ctx *ctx,
 		struct damon_target *t, struct damon_region *r,
 		unsigned long sz_r);
 
+static bool __damos_valid_target(struct damon_region *r, struct damos *s)
+{
+	unsigned long sz;
+
+	sz = r->ar.end - r->ar.start;
+	return s->min_sz_region <= sz && sz <= s->max_sz_region &&
+		s->min_nr_accesses <= r->nr_accesses &&
+		r->nr_accesses <= s->max_nr_accesses &&
+		s->min_age_region <= r->age && r->age <= s->max_age_region;
+}
+
+static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
+		struct damon_region *r, struct damos *s)
+{
+	bool ret = __damos_valid_target(r, s);
+
+	if (!ret || !s->quota.esz || !c->primitive.get_scheme_score)
+		return ret;
+
+	return c->primitive.get_scheme_score(c, t, r, s) >= s->quota.min_score;
+}
+
 static void damon_do_apply_schemes(struct damon_ctx *c,
 				   struct damon_target *t,
 				   struct damon_region *r)
@@ -591,13 +617,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			quota->charge_addr_from = 0;
 		}
 
-		/* Check the target regions condition */
-		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)
+		if (!damos_valid_target(c, t, r, s))
 			continue;
 
 		/* Apply the scheme */
@@ -661,6 +681,8 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 
 	damon_for_each_scheme(s, c) {
 		struct damos_quota *quota = &s->quota;
+		unsigned long cumulated_sz;
+		unsigned int score, max_score = 0;
 
 		if (!quota->ms && !quota->sz)
 			continue;
@@ -674,6 +696,32 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 			quota->charged_sz = 0;
 			damos_set_effective_quota(quota);
 		}
+
+		if (!c->primitive.get_scheme_score)
+			continue;
+
+		/* Fill up the score histogram */
+		memset(quota->histogram, 0, sizeof(quota->histogram));
+		damon_for_each_target(t, c) {
+			damon_for_each_region(r, t) {
+				if (!__damos_valid_target(r, s))
+					continue;
+				score = c->primitive.get_scheme_score(
+						c, t, r, s);
+				quota->histogram[score] +=
+					r->ar.end - r->ar.start;
+				if (score > max_score)
+					max_score = score;
+			}
+		}
+
+		/* Set the min score limit */
+		for (cumulated_sz = 0, score = max_score; ; score--) {
+			cumulated_sz += quota->histogram[score];
+			if (cumulated_sz >= quota->esz || !score)
+				break;
+		}
+		quota->min_score = score;
 	}
 
 	damon_for_each_target(t, c) {
-- 
2.17.1

[PATCH 08/15] mm/damon/vaddr,paddr: Support pageout prioritization

[SeongJae Park]

This commit makes the default monitoring primitives for virtual address
spaces and the physical address sapce to support memory regions
prioritization for 'PAGEOUT' DAMOS action.  It calculates hotness of
each region as weighted sum of 'nr_accesses' and 'age' of the region and
get the priority score as reverse of the hotness, so that cold regions
can be paged out first.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h   |  4 ++++
 mm/damon/paddr.c        | 14 +++++++++++++
 mm/damon/prmtv-common.c | 46 +++++++++++++++++++++++++++++++++++++++++
 mm/damon/prmtv-common.h |  3 +++
 mm/damon/vaddr.c        | 15 ++++++++++++++
 5 files changed, 82 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 999918a07444..bdbb70db5e86 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -421,6 +421,8 @@ 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);
+int damon_va_scheme_score(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 */
@@ -431,6 +433,8 @@ void damon_va_set_primitives(struct damon_ctx *ctx);
 void damon_pa_prepare_access_checks(struct damon_ctx *ctx);
 unsigned int damon_pa_check_accesses(struct damon_ctx *ctx);
 bool damon_pa_target_valid(void *t);
+int damon_pa_scheme_score(struct damon_ctx *context, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme);
 void damon_pa_set_primitives(struct damon_ctx *ctx);
 
 #endif	/* CONFIG_DAMON_PADDR */
diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 957ada55de77..a496d6f203d6 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -246,6 +246,19 @@ int damon_pa_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 	return 0;
 }
 
+int damon_pa_scheme_score(struct damon_ctx *context, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme)
+{
+	switch (scheme->action) {
+	case DAMOS_PAGEOUT:
+		return damon_pageout_score(context, r, scheme);
+	default:
+		break;
+	}
+
+	return DAMOS_MAX_SCORE;
+}
+
 void damon_pa_set_primitives(struct damon_ctx *ctx)
 {
 	ctx->primitive.init = NULL;
@@ -256,4 +269,5 @@ void damon_pa_set_primitives(struct damon_ctx *ctx)
 	ctx->primitive.target_valid = damon_pa_target_valid;
 	ctx->primitive.cleanup = NULL;
 	ctx->primitive.apply_scheme = damon_pa_apply_scheme;
+	ctx->primitive.get_scheme_score = damon_pa_scheme_score;
 }
diff --git a/mm/damon/prmtv-common.c b/mm/damon/prmtv-common.c
index 7e62ee54fb54..92a04f5831d6 100644
--- a/mm/damon/prmtv-common.c
+++ b/mm/damon/prmtv-common.c
@@ -85,3 +85,49 @@ void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr)
 	put_page(page);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 }
+
+#define DAMON_MAX_SUBSCORE	(100)
+#define DAMON_MAX_AGE_IN_LOG	(32)
+
+int damon_pageout_score(struct damon_ctx *c, struct damon_region *r,
+			struct damos *s)
+{
+	unsigned int max_nr_accesses;
+	int freq_subscore;
+	unsigned int age_in_sec;
+	int age_in_log, age_subscore;
+	unsigned int freq_weight = s->quota.weight_nr_accesses;
+	unsigned int age_weight = s->quota.weight_age;
+	int hotness;
+
+	max_nr_accesses = c->aggr_interval / c->sample_interval;
+	freq_subscore = r->nr_accesses * DAMON_MAX_SUBSCORE / max_nr_accesses;
+
+	age_in_sec = (unsigned long)r->age * c->aggr_interval / 1000000;
+	for (age_in_log = 0; age_in_log < DAMON_MAX_AGE_IN_LOG && age_in_sec;
+			age_in_log++, age_in_sec >>= 1)
+		;
+
+	/* If frequency is 0, higher age means it's colder */
+	if (freq_subscore == 0)
+		age_in_log *= -1;
+
+	/*
+	 * Now age_in_log is in [-DAMON_MAX_AGE_IN_LOG, DAMON_MAX_AGE_IN_LOG].
+	 * Scale it to be in [0, 100] and set it as age subscore.
+	 */
+	age_in_log += DAMON_MAX_AGE_IN_LOG;
+	age_subscore = age_in_log * DAMON_MAX_SUBSCORE /
+		DAMON_MAX_AGE_IN_LOG / 2;
+
+	hotness = (freq_weight * freq_subscore + age_weight * age_subscore);
+	if (freq_weight + age_weight)
+		hotness /= freq_weight + age_weight;
+	/*
+	 * Transform it to fit in [0, DAMOS_MAX_SCORE]
+	 */
+	hotness = hotness * DAMOS_MAX_SCORE / DAMON_MAX_SUBSCORE;
+
+	/* Return coldness of the region */
+	return DAMOS_MAX_SCORE - hotness;
+}
diff --git a/mm/damon/prmtv-common.h b/mm/damon/prmtv-common.h
index 7093d19e5d42..61f27037603e 100644
--- a/mm/damon/prmtv-common.h
+++ b/mm/damon/prmtv-common.h
@@ -15,3 +15,6 @@ struct page *damon_get_page(unsigned long pfn);
 
 void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr);
 void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr);
+
+int damon_pageout_score(struct damon_ctx *c, struct damon_region *r,
+			struct damos *s);
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 758501b8d97d..675cd8c7df9b 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -633,6 +633,20 @@ int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 	return damos_madvise(t, r, madv_action);
 }
 
+int damon_va_scheme_score(struct damon_ctx *context, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme)
+{
+
+	switch (scheme->action) {
+	case DAMOS_PAGEOUT:
+		return damon_pageout_score(context, r, scheme);
+	default:
+		break;
+	}
+
+	return DAMOS_MAX_SCORE;
+}
+
 void damon_va_set_primitives(struct damon_ctx *ctx)
 {
 	ctx->primitive.init = damon_va_init;
@@ -643,6 +657,7 @@ void damon_va_set_primitives(struct damon_ctx *ctx)
 	ctx->primitive.target_valid = damon_va_target_valid;
 	ctx->primitive.cleanup = NULL;
 	ctx->primitive.apply_scheme = damon_va_apply_scheme;
+	ctx->primitive.get_scheme_score = damon_va_scheme_score;
 }
 
 #include "vaddr-test.h"
-- 
2.17.1

[PATCH 09/15] mm/damon/dbgfs: Support prioritization weights

[SeongJae Park]

This commit allows DAMON debugfs interface users set the prioritization
weights by putting three more numbers to the 'schemes' file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 097e6745ba75..20c4feb8b918 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -105,13 +105,16 @@ 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 %lu %lu %lu %lu %lu\n",
+				"%lu %lu %u %u %u %u %d %lu %lu %lu %u %u %u %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->quota.ms, s->quota.sz,
 				s->quota.reset_interval,
+				s->quota.weight_sz,
+				s->quota.weight_nr_accesses,
+				s->quota.weight_age,
 				s->stat_count, s->stat_sz);
 		if (!rc)
 			return -ENOMEM;
@@ -193,11 +196,14 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 	while (pos < len && *nr_schemes < max_nr_schemes) {
 		struct damos_quota quota = {};
 
-		ret = sscanf(&str[pos], "%lu %lu %u %u %u %u %u %lu %lu %lu%n",
+		ret = sscanf(&str[pos],
+				"%lu %lu %u %u %u %u %u %lu %lu %lu %u %u %u%n",
 				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
 				&min_age, &max_age, &action, &quota.ms,
-				&quota.sz, &quota.reset_interval, &parsed);
-		if (ret != 10)
+				&quota.sz, &quota.reset_interval,
+				&quota.weight_sz, &quota.weight_nr_accesses,
+				&quota.weight_age, &parsed);
+		if (ret != 13)
 			break;
 		if (!damos_action_valid(action)) {
 			pr_err("wrong action %d\n", action);
-- 
2.17.1

[PATCH 10/15] tools/selftests/damon: Update for regions prioritization of schemes

[SeongJae Park]

This commit updates the DAMON selftests for 'schemes' debugfs file, as
the file format is updated.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/debugfs_attrs.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/damon/debugfs_attrs.sh b/tools/testing/selftests/damon/debugfs_attrs.sh
index 8e33a7b584e7..466dbeb37e31 100755
--- a/tools/testing/selftests/damon/debugfs_attrs.sh
+++ b/tools/testing/selftests/damon/debugfs_attrs.sh
@@ -63,10 +63,10 @@ echo "$orig_content" > "$file"
 file="$DBGFS/schemes"
 orig_content=$(cat "$file")
 
-test_write_succ "$file" "1 2 3 4 5 6 4 0 0 0" \
+test_write_succ "$file" "1 2 3 4 5 6 4 0 0 0 1 2 3" \
 	"$orig_content" "valid input"
 test_write_fail "$file" "1 2
-3 4 5 6 3 0 0 0" "$orig_content" "multi lines"
+3 4 5 6 3 0 0 0 1 2 3" "$orig_content" "multi lines"
 test_write_succ "$file" "" "$orig_content" "disabling"
 echo "$orig_content" > "$file"
 
-- 
2.17.1

[PATCH 11/15] mm/damon/schemes: Activate schemes based on a watermarks mechanism

[SeongJae Park]

DAMON-based operation schemes need to be manually turned on and off.  In
some use cases, however, the condition for turning a scheme on and off
would depend on the system's situation.  For example, schemes for
proactive pages reclamation would need to be turned on when some memory
pressure is detected, and turned off when the system has enough free
memory.

For easier control of schemes activation based on the system situation,
this commit introduces a watermarks-based mechanism.  The client can
describe the watermark metric (e.g., amount of free memory in the
system), watermark check interval, and three watermarks, namely high,
mid, and low.  If the scheme is deactivated, it only gets the metric and
compare that to the three watermarks for every check interval.  If the
metric is higher than the high watermark, the scheme is deactivated.  If
the metric is between the mid watermark and the low watermark, the
scheme is activated.  If the metric is lower than the low watermark, the
scheme is deactivated again.  This is to allow users fall back to
traditional page-granularity mechanisms.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 52 ++++++++++++++++++++++-
 mm/damon/core.c       | 97 ++++++++++++++++++++++++++++++++++++++++++-
 mm/damon/dbgfs.c      |  5 ++-
 3 files changed, 151 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index bdbb70db5e86..239681d657a8 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -146,6 +146,45 @@ struct damos_quota {
 	unsigned int min_score;
 };
 
+/**
+ * enum damos_wmark_metric - Represents the watermark metric.
+ *
+ * @DAMOS_WMARK_NONE:		Ignore the watermarks of the given scheme.
+ * @DAMOS_WMARK_FREE_MEM_RATE:	Free memory rate of the system in [0,1000].
+ */
+enum damos_wmark_metric {
+	DAMOS_WMARK_NONE,
+	DAMOS_WMARK_FREE_MEM_RATE,
+};
+
+/**
+ * struct damos_watermarks - Controls when a given scheme should be activated.
+ * @metric:	Metric for the watermarks.
+ * @interval:	Watermarks check time interval in microseconds.
+ * @high:	High watermark.
+ * @mid:	Middle watermark.
+ * @low:	Low watermark.
+ *
+ * If &metric is &DAMOS_WMARK_NONE, the scheme is always active.  Being active
+ * means DAMON does monitoring and applying the action of the scheme to
+ * appropriate memory regions.  Else, DAMON checks &metric of the system for at
+ * least every &interval microseconds and works as below.
+ *
+ * If &metric is higher than &high, the scheme is inactivated.  If &metric is
+ * between &mid and &low, the scheme is activated.  If &metric is lower than
+ * &low, the scheme is inactivated.
+ */
+struct damos_watermarks {
+	enum damos_wmark_metric metric;
+	unsigned long interval;
+	unsigned long high;
+	unsigned long mid;
+	unsigned long low;
+
+/* private: */
+	bool activated;
+};
+
 /**
  * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
  * @min_sz_region:	Minimum size of target regions.
@@ -156,6 +195,7 @@ struct damos_quota {
  * @max_age_region:	Maximum age of target regions.
  * @action:		&damo_action to be applied to the target regions.
  * @quota:		Control the aggressiveness of this scheme.
+ * @wmarks:		Watermarks for automated (in)activation of this scheme.
  * @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.
@@ -166,6 +206,14 @@ struct damos_quota {
  * those.  To avoid consuming too much CPU time or IO resources for the
  * &action, &quota is used.
  *
+ * To do the work only when needed, schemes can be activated for specific
+ * system situations using &wmarks.  If all schemes that registered to the
+ * monitoring context are inactive, DAMON stops monitoring either, and just
+ * repeatedly checks the watermarks.
+ *
+ * If all schemes that registered to a &struct damon_ctx are inactive, DAMON
+ * stops monitoring and just repeatedly checks the watermarks.
+ *
  * After applying the &action to each region, &stat_count and &stat_sz is
  * updated to reflect the number of regions and total size of regions that the
  * &action is applied.
@@ -179,6 +227,7 @@ struct damos {
 	unsigned int max_age_region;
 	enum damos_action action;
 	struct damos_quota quota;
+	struct damos_watermarks wmarks;
 	unsigned long stat_count;
 	unsigned long stat_sz;
 	struct list_head list;
@@ -384,7 +433,8 @@ 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_quota *quota);
+		enum damos_action action, struct damos_quota *quota,
+		struct damos_watermarks *wmarks);
 void damon_add_scheme(struct damon_ctx *ctx, struct damos *s);
 void damon_destroy_scheme(struct damos *s);
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index fad25778e2ec..6993c60ae31c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -10,6 +10,7 @@
 #include <linux/damon.h>
 #include <linux/delay.h>
 #include <linux/kthread.h>
+#include <linux/mm.h>
 #include <linux/random.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -90,7 +91,8 @@ 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_quota *quota)
+		enum damos_action action, struct damos_quota *quota,
+		struct damos_watermarks *wmarks)
 {
 	struct damos *scheme;
 
@@ -122,6 +124,13 @@ struct damos *damon_new_scheme(
 	scheme->quota.charge_target_from = NULL;
 	scheme->quota.charge_addr_from = 0;
 
+	scheme->wmarks.metric = wmarks->metric;
+	scheme->wmarks.interval = wmarks->interval;
+	scheme->wmarks.high = wmarks->high;
+	scheme->wmarks.mid = wmarks->mid;
+	scheme->wmarks.low = wmarks->low;
+	scheme->wmarks.activated = true;
+
 	return scheme;
 }
 
@@ -582,6 +591,9 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		unsigned long sz = r->ar.end - r->ar.start;
 		struct timespec64 begin, end;
 
+		if (!s->wmarks.activated)
+			continue;
+
 		/* Check the quota */
 		if (quota->esz && quota->charged_sz >= quota->esz)
 			continue;
@@ -684,6 +696,9 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 		unsigned long cumulated_sz;
 		unsigned int score, max_score = 0;
 
+		if (!s->wmarks.activated)
+			continue;
+
 		if (!quota->ms && !quota->sz)
 			continue;
 
@@ -924,6 +939,83 @@ static bool kdamond_need_stop(struct damon_ctx *ctx)
 	return true;
 }
 
+static unsigned long damos_wmark_metric_value(enum damos_wmark_metric metric)
+{
+	struct sysinfo i;
+
+	switch (metric) {
+	case DAMOS_WMARK_FREE_MEM_RATE:
+		si_meminfo(&i);
+		return i.freeram * 1000 / i.totalram;
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+/*
+ * Returns zero if the scheme is active.  Else, returns time to wait for next
+ * watermark check in micro-seconds.
+ */
+static unsigned long damos_wmark_wait_us(struct damos *scheme)
+{
+	unsigned long metric;
+
+	if (scheme->wmarks.metric == DAMOS_WMARK_NONE)
+		return 0;
+
+	metric = damos_wmark_metric_value(scheme->wmarks.metric);
+	/* higher than high watermark or lower than low watermark */
+	if (metric > scheme->wmarks.high || scheme->wmarks.low > metric) {
+		if (scheme->wmarks.activated)
+			pr_debug("inactivate a scheme (%d) for %s wmark\n",
+					scheme->action,
+					metric > scheme->wmarks.high ?
+					"high" : "low");
+		scheme->wmarks.activated = false;
+		return scheme->wmarks.interval;
+	}
+
+	/* inactive and higher than middle watermark */
+	if ((scheme->wmarks.high >= metric && metric >= scheme->wmarks.mid) &&
+			!scheme->wmarks.activated)
+		return scheme->wmarks.interval;
+
+	if (!scheme->wmarks.activated)
+		pr_debug("activate a scheme (%d)\n", scheme->action);
+	scheme->wmarks.activated = true;
+	return 0;
+}
+
+static void kdamond_usleep(unsigned long usecs)
+{
+	if (usecs > 100 * 1000)
+		schedule_timeout_interruptible(usecs_to_jiffies(usecs));
+	else
+		usleep_range(usecs, usecs + 1);
+}
+
+/* Returns negative error code if it's not activated but should return */
+static int kdamond_wait_activation(struct damon_ctx *ctx)
+{
+	struct damos *s;
+	unsigned long wait_time;
+	unsigned long min_wait_time = 0;
+
+	while (!kdamond_need_stop(ctx)) {
+		damon_for_each_scheme(s, ctx) {
+			wait_time = damos_wmark_wait_us(s);
+			if (!min_wait_time || wait_time < min_wait_time)
+				min_wait_time = wait_time;
+		}
+		if (!min_wait_time)
+			return 0;
+
+		kdamond_usleep(min_wait_time);
+	}
+	return -EBUSY;
+}
+
 static void set_kdamond_stop(struct damon_ctx *ctx)
 {
 	mutex_lock(&ctx->kdamond_lock);
@@ -952,6 +1044,9 @@ static int kdamond_fn(void *data)
 	sz_limit = damon_region_sz_limit(ctx);
 
 	while (!kdamond_need_stop(ctx)) {
+		if (kdamond_wait_activation(ctx))
+			continue;
+
 		if (ctx->primitive.prepare_access_checks)
 			ctx->primitive.prepare_access_checks(ctx);
 		if (ctx->callback.after_sampling &&
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 20c4feb8b918..9f13060d1058 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -195,6 +195,9 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 	*nr_schemes = 0;
 	while (pos < len && *nr_schemes < max_nr_schemes) {
 		struct damos_quota quota = {};
+		struct damos_watermarks wmarks = {
+			.metric = DAMOS_WMARK_NONE,
+		};
 
 		ret = sscanf(&str[pos],
 				"%lu %lu %u %u %u %u %u %lu %lu %lu %u %u %u%n",
@@ -212,7 +215,7 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 
 		pos += parsed;
 		scheme = damon_new_scheme(min_sz, max_sz, min_nr_a, max_nr_a,
-				min_age, max_age, action, &quota);
+				min_age, max_age, action, &quota, &wmarks);
 		if (!scheme)
 			goto fail;
 
-- 
2.17.1

[PATCH 12/15] mm/damon/dbgfs: Support watermarks

[SeongJae Park]

This commit updates DAMON debugfs interface to support the watermarks
based schemes activation.  For this, now 'schemes' file receives five
more values.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 9f13060d1058..6828e463348b 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -105,7 +105,7 @@ 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 %lu %lu %lu %u %u %u %lu %lu\n",
+				"%lu %lu %u %u %u %u %d %lu %lu %lu %u %u %u %d %lu %lu %lu %lu %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,
@@ -115,6 +115,8 @@ static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 				s->quota.weight_sz,
 				s->quota.weight_nr_accesses,
 				s->quota.weight_age,
+				s->wmarks.metric, s->wmarks.interval,
+				s->wmarks.high, s->wmarks.mid, s->wmarks.low,
 				s->stat_count, s->stat_sz);
 		if (!rc)
 			return -ENOMEM;
@@ -195,18 +197,18 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 	*nr_schemes = 0;
 	while (pos < len && *nr_schemes < max_nr_schemes) {
 		struct damos_quota quota = {};
-		struct damos_watermarks wmarks = {
-			.metric = DAMOS_WMARK_NONE,
-		};
+		struct damos_watermarks wmarks;
 
 		ret = sscanf(&str[pos],
-				"%lu %lu %u %u %u %u %u %lu %lu %lu %u %u %u%n",
+				"%lu %lu %u %u %u %u %u %lu %lu %lu %u %u %u %u %lu %lu %lu %lu%n",
 				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
 				&min_age, &max_age, &action, &quota.ms,
 				&quota.sz, &quota.reset_interval,
 				&quota.weight_sz, &quota.weight_nr_accesses,
-				&quota.weight_age, &parsed);
-		if (ret != 13)
+				&quota.weight_age, &wmarks.metric,
+				&wmarks.interval, &wmarks.high, &wmarks.mid,
+				&wmarks.low, &parsed);
+		if (ret != 18)
 			break;
 		if (!damos_action_valid(action)) {
 			pr_err("wrong action %d\n", action);
-- 
2.17.1

[PATCH 13/15] selftests/damon: Support watermarks

[SeongJae Park]

This commit updates DAMON selftests for 'schemes' debugfs file to
reflect the changes in the format.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/debugfs_attrs.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/damon/debugfs_attrs.sh b/tools/testing/selftests/damon/debugfs_attrs.sh
index 466dbeb37e31..196b6640bf37 100755
--- a/tools/testing/selftests/damon/debugfs_attrs.sh
+++ b/tools/testing/selftests/damon/debugfs_attrs.sh
@@ -63,10 +63,10 @@ echo "$orig_content" > "$file"
 file="$DBGFS/schemes"
 orig_content=$(cat "$file")
 
-test_write_succ "$file" "1 2 3 4 5 6 4 0 0 0 1 2 3" \
+test_write_succ "$file" "1 2 3 4 5 6 4 0 0 0 1 2 3 1 100 3 2 1" \
 	"$orig_content" "valid input"
 test_write_fail "$file" "1 2
-3 4 5 6 3 0 0 0 1 2 3" "$orig_content" "multi lines"
+3 4 5 6 3 0 0 0 1 2 3 1 100 3 2 1" "$orig_content" "multi lines"
 test_write_succ "$file" "" "$orig_content" "disabling"
 echo "$orig_content" > "$file"
 
-- 
2.17.1

[PATCH 14/15] mm/damon: Introduce DAMON-based Reclamation (DAMON_RECLAIM)

[SeongJae Park]

This commit implements a new kernel subsystem that finds cold memory
regions using DAMON and reclaims those immediately.  It is intended to
be used as proactive lightweigh reclamation logic for light memory
pressure.  For heavy memory pressure, it could be inactivated and fall
back to the traditional page-scanning based reclamation.

It's implemented on top of DAMON framework to use the DAMON-based
Operation Schemes (DAMOS) feature.  It utilizes all the DAMOS features
including speed limit, prioritization, and watermarks.

It could be enabled and tuned in boot time via the kernel boot
parameter, and in run time via its module parameters
('/sys/module/damon_reclaim/parameters/') interface.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/Kconfig   |  12 ++
 mm/damon/Makefile  |   1 +
 mm/damon/reclaim.c | 354 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 367 insertions(+)
 create mode 100644 mm/damon/reclaim.c

diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index ca33b289ebbe..5bcf05851ad0 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -73,4 +73,16 @@ config DAMON_DBGFS_KUNIT_TEST
 
 	  If unsure, say N.
 
+config DAMON_RECLAIM
+	bool "Build DAMON-based reclaim (DAMON_RECLAIM)"
+	depends on DAMON_PADDR
+	help
+	  This builds the DAMON-based reclamation subsystem.  It finds pages
+	  that not accessed for a long time (cold) using DAMON and reclaim
+	  those.
+
+	  This is suggested to be used as a proactive and lightweight
+	  reclamation under light memory pressure, while the traditional page
+	  scanning-based reclamation is used for heavy pressure.
+
 endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
index 8d9b0df79702..f7d5ac377a2b 100644
--- a/mm/damon/Makefile
+++ b/mm/damon/Makefile
@@ -4,3 +4,4 @@ obj-$(CONFIG_DAMON)		:= core.o
 obj-$(CONFIG_DAMON_VADDR)	+= prmtv-common.o vaddr.o
 obj-$(CONFIG_DAMON_PADDR)	+= prmtv-common.o paddr.o
 obj-$(CONFIG_DAMON_DBGFS)	+= dbgfs.o
+obj-$(CONFIG_DAMON_RECLAIM)	+= reclaim.o
diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
new file mode 100644
index 000000000000..f5ae4c422555
--- /dev/null
+++ b/mm/damon/reclaim.c
@@ -0,0 +1,354 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DAMON-based page reclamation
+ *
+ * Author: SeongJae Park <sj@kernel.org>
+ */
+
+#define pr_fmt(fmt) "damon-reclaim: " fmt
+
+#include <linux/damon.h>
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/workqueue.h>
+
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "damon_reclaim."
+
+/*
+ * Enable or disable DAMON_RECLAIM.
+ *
+ * You can enable DAMON_RCLAIM by setting the value of this parameter as ``Y``.
+ * Setting it as ``N`` disables DAMON_RECLAIM.  Note that DAMON_RECLAIM could
+ * do no real monitoring and reclamation due to the watermarks-based activation
+ * condition.  Refer to below descriptions for the watermarks parameter for
+ * this.
+ */
+static bool enabled __read_mostly;
+module_param(enabled, bool, 0600);
+
+/*
+ * Time threshold for cold memory regions identification in microseconds.
+ *
+ * If a memory region is not accessed for this or longer time, DAMON_RECLAIM
+ * identifies the region as cold, and reclaims.  120 seconds by default.
+ */
+static unsigned long min_age __read_mostly = 120000000;
+module_param(min_age, ulong, 0600);
+
+/*
+ * Limit of time for trying the reclamation in milliseconds.
+ *
+ * DAMON_RECLAIM tries to use only up to this time within a time window
+ * (quota_reset_interval_ms) for trying reclamation of cold pages.  This can be
+ * used for limiting CPU consumption of DAMON_RECLAIM.  If the value is zero,
+ * the limit is disabled.
+ *
+ * 10 ms by default.
+ */
+static unsigned long quota_ms __read_mostly = 10;
+module_param(quota_ms, ulong, 0600);
+
+/*
+ * Limit of size of memory for the reclamation in bytes.
+ *
+ * DAMON_RECLAIM charges amount of memory which it tried to reclaim within a
+ * time window (quota_reset_interval_ms) and makes no more than this limit is
+ * tried.  This can be used for limiting consumption of CPU and IO.  If this
+ * value is zero, the limit is disabled.
+ *
+ * 128 MiB by default.
+ */
+static unsigned long quota_sz __read_mostly = 128 * 1024 * 1024;
+module_param(quota_sz, ulong, 0600);
+
+/*
+ * The time/size quota charge reset interval in milliseconds.
+ *
+ * The charge reset interval for the quota of time (quota_ms) and size
+ * (quota_sz).  That is, DAMON_RECLAIM does not try reclamation for more than
+ * quota_ms milliseconds or quota_sz bytes within quota_reset_interval_ms
+ * milliseconds.
+ *
+ * 1 second by default.
+ */
+static unsigned long quota_reset_interval_ms __read_mostly = 1000;
+module_param(quota_reset_interval_ms, ulong, 0600);
+
+/*
+ * The watermarks check time interval in microseconds.
+ *
+ * Minimal time to wait before checking the watermarks, when DAMON_RECLAIM is
+ * enabled but inactive due to its watermarks rule.  5 seconds by default.
+ */
+static unsigned long wmarks_interval __read_mostly = 5000000;
+module_param(wmarks_interval, ulong, 0600);
+
+/*
+ * Free memory rate (per thousand) for the high watermark.
+ *
+ * If free memory of the system in bytes per thousand bytes is higher than
+ * this, DAMON_RECLAIM becomes inactive, so it does nothing but periodically
+ * checks the watermarks.  500 (50%) by default.
+ */
+static unsigned long wmarks_high __read_mostly = 500;
+module_param(wmarks_high, ulong, 0600);
+
+/*
+ * Free memory rate (per thousand) for the middle watermark.
+ *
+ * If free memory of the system in bytes per thousand bytes is between this and
+ * the low watermark, DAMON_RECLAIM becomes active, so starts the monitoring
+ * and the reclaiming.  400 (40%) by default.
+ */
+static unsigned long wmarks_mid __read_mostly = 400;
+module_param(wmarks_mid, ulong, 0600);
+
+/*
+ * Free memory rate (per thousand) for the low watermark.
+ *
+ * If free memory of the system in bytes per thousand bytes is lower than this,
+ * DAMON_RECLAIM becomes inactive, so it does nothing but periodically checks
+ * the watermarks.  In the case, the system falls back to the LRU-based page
+ * granularity reclamation logic.  200 (20%) by default.
+ */
+static unsigned long wmarks_low __read_mostly = 200;
+module_param(wmarks_low, ulong, 0600);
+
+/*
+ * Sampling interval for the monitoring in microseconds.
+ *
+ * The sampling interval of DAMON for the cold memory monitoring.  Please refer
+ * to the DAMON documentation for more detail.  5 ms by default.
+ */
+static unsigned long sample_interval __read_mostly = 5000;
+module_param(sample_interval, ulong, 0600);
+
+/*
+ * Aggregation interval for the monitoring in microseconds.
+ *
+ * The aggregation interval of DAMON for the cold memory monitoring.  Please
+ * refer to the DAMON documentation for more detail.  100 ms by default.
+ */
+static unsigned long aggr_interval __read_mostly = 100000;
+module_param(aggr_interval, ulong, 0600);
+
+/*
+ * Minimum number of monitoring regions.
+ *
+ * The minimal number of monitoring regions of DAMON for the cold memory
+ * monitoring.  This can be used to set lower-bound of the monitoring quality.
+ * But, setting this too high could result in increased monitoring overhead.
+ * Please refer to the DAMON documentation for more detail.  10 by default.
+ */
+static unsigned long min_nr_regions __read_mostly = 10;
+module_param(min_nr_regions, ulong, 0600);
+
+/*
+ * Maximum number of monitoring regions.
+ *
+ * The maximum number of monitoring regions of DAMON for the cold memory
+ * monitoring.  This can be used to set upper-bound of the monitoring overhead.
+ * However, setting this too low could result in bad monitoring quality.
+ * Please refer to the DAMON documentation for more detail.  1000 by default.
+ */
+static unsigned long max_nr_regions __read_mostly = 1000;
+module_param(max_nr_regions, ulong, 0600);
+
+/*
+ * Start of the target memory region in physical address.
+ *
+ * The start physical address of memory region that DAMON_RECLAIM will do work
+ * against.  By default, biggest System RAM is used as the region.
+ */
+static unsigned long monitor_region_start __read_mostly;
+module_param(monitor_region_start, ulong, 0600);
+
+/*
+ * End of the target memory region in physical address.
+ *
+ * The end physical address of memory region that DAMON_RECLAIM will do work
+ * against.  By default, biggest System RAM is used as the region.
+ */
+static unsigned long monitor_region_end __read_mostly;
+module_param(monitor_region_end, ulong, 0600);
+
+/*
+ * PID of the DAMON thread
+ *
+ * If DAMON_RECLAIM is enabled, this becomes the PID of the worker thread.
+ * Else, -1.
+ */
+static int kdamond_pid __read_mostly = -1;
+module_param(kdamond_pid, int, 0400);
+
+static struct damon_ctx *ctx;
+static struct damon_target *target;
+
+struct damon_reclaim_ram_walk_arg {
+	unsigned long start;
+	unsigned long end;
+};
+
+static int walk_system_ram(struct resource *res, void *arg)
+{
+	struct damon_reclaim_ram_walk_arg *a = arg;
+
+	if (a->end - a->start < res->end - res->start) {
+		a->start = res->start;
+		a->end = res->end;
+	}
+	return 0;
+}
+
+/*
+ * Find biggest 'System RAM' resource and store its start and end address in
+ * @start and @end, respectively.  If no System RAM is found, returns false.
+ */
+static bool get_monitoring_region(unsigned long *start, unsigned long *end)
+{
+	struct damon_reclaim_ram_walk_arg arg = {};
+
+	walk_system_ram_res(0, ULONG_MAX, &arg, walk_system_ram);
+	if (arg.end <= arg.start)
+		return false;
+
+	*start = arg.start;
+	*end = arg.end;
+	return true;
+}
+
+static struct damos *damon_reclaim_new_scheme(void)
+{
+	struct damos_watermarks wmarks = {
+		.metric = DAMOS_WMARK_FREE_MEM_RATE,
+		.interval = wmarks_interval,
+		.high = wmarks_high,
+		.mid = wmarks_mid,
+		.low = wmarks_low,
+	};
+	struct damos_quota quota = {
+		/*
+		 * Do not try reclamation for more than quota_ms milliseconds
+		 * or quota_sz bytes within quota_reset_interval_ms.
+		 */
+		.ms = quota_ms,
+		.sz = quota_sz,
+		.reset_interval = quota_reset_interval_ms,
+		/* Within the quota, page out older regions first. */
+		.weight_sz = 0,
+		.weight_nr_accesses = 0,
+		.weight_age = 1
+	};
+	struct damos *scheme = damon_new_scheme(
+			/* Find regions having PAGE_SIZE or larger size */
+			PAGE_SIZE, ULONG_MAX,
+			/* and not accessed at all */
+			0, 0,
+			/* for min_age or more micro-seconds, and */
+			min_age / aggr_interval, UINT_MAX,
+			/* page out those, as soon as found */
+			DAMOS_PAGEOUT,
+			/* under the quota. */
+			&quota,
+			/* (De)activate this according to the watermarks. */
+			&wmarks);
+
+	return scheme;
+}
+
+static int damon_reclaim_turn(bool on)
+{
+	struct damon_region *region;
+	struct damos *scheme;
+	int err;
+
+	if (!on) {
+		err = damon_stop(&ctx, 1);
+		if (!err)
+			kdamond_pid = -1;
+		return err;
+	}
+
+	err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
+			min_nr_regions, max_nr_regions);
+	if (err)
+		return err;
+
+	if (monitor_region_start > monitor_region_end)
+		return -EINVAL;
+	if (!monitor_region_start && !monitor_region_end &&
+			!get_monitoring_region(&monitor_region_start,
+				&monitor_region_end))
+		return -EINVAL;
+	/* DAMON will free this on its own when finish monitoring */
+	region = damon_new_region(monitor_region_start, monitor_region_end);
+	if (!region)
+		return -ENOMEM;
+	damon_add_region(region, target);
+
+	/* Will be freed by 'damon_set_schemes()' below */
+	scheme = damon_reclaim_new_scheme();
+	if (!scheme)
+		goto free_region_out;
+	err = damon_set_schemes(ctx, &scheme, 1);
+	if (err)
+		goto free_scheme_out;
+
+	err = damon_start(&ctx, 1);
+	if (!err) {
+		kdamond_pid = ctx->kdamond->pid;
+		return 0;
+	}
+
+free_scheme_out:
+	damon_destroy_scheme(scheme);
+free_region_out:
+	damon_destroy_region(region, target);
+	return err;
+}
+
+#define ENABLE_CHECK_INTERVAL_MS	1000
+static struct delayed_work damon_reclaim_timer;
+static void damon_reclaim_timer_fn(struct work_struct *work)
+{
+	static bool last_enabled;
+	bool now_enabled;
+
+	now_enabled = enabled;
+	if (last_enabled != now_enabled) {
+		if (!damon_reclaim_turn(now_enabled))
+			last_enabled = now_enabled;
+		else
+			enabled = last_enabled;
+	}
+
+	schedule_delayed_work(&damon_reclaim_timer,
+			msecs_to_jiffies(ENABLE_CHECK_INTERVAL_MS));
+}
+static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);
+
+static int __init damon_reclaim_init(void)
+{
+	ctx = damon_new_ctx();
+	if (!ctx)
+		return -ENOMEM;
+
+	damon_pa_set_primitives(ctx);
+
+	/* 4242 means nothing but fun */
+	target = damon_new_target(4242);
+	if (!target) {
+		damon_destroy_ctx(ctx);
+		return -ENOMEM;
+	}
+	damon_add_target(ctx, target);
+
+	schedule_delayed_work(&damon_reclaim_timer, 0);
+	return 0;
+}
+
+module_init(damon_reclaim_init);
-- 
2.17.1

[PATCH 15/15] Documentation/admin-guide/mm/damon: Add a document for DAMON_RECLAIM

[SeongJae Park]

This commit adds an admin-guide document for DAMON-based Reclamation.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/index.rst  |   1 +
 .../admin-guide/mm/damon/reclaim.rst          | 235 ++++++++++++++++++
 2 files changed, 236 insertions(+)
 create mode 100644 Documentation/admin-guide/mm/damon/reclaim.rst

diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst
index 8c5dde3a5754..61aff88347f3 100644
--- a/Documentation/admin-guide/mm/damon/index.rst
+++ b/Documentation/admin-guide/mm/damon/index.rst
@@ -13,3 +13,4 @@ optimize those.
 
    start
    usage
+   reclaim
diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst
new file mode 100644
index 000000000000..fb9def3a7355
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/reclaim.rst
@@ -0,0 +1,235 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+DAMON-based Reclamation
+=======================
+
+DAMON-based Reclamation (DAMON_RECLAIM) is a static kernel module that aimed to
+be used for proactive and lightweight reclamation under light memory pressure.
+It doesn't aim to replace the LRU-list based page_granularity reclamation, but
+to be selectively used for different level of memory pressure and requirements.
+
+Where Proactive Reclamation is Required?
+========================================
+
+On general memory over-committed systems, proactively reclaiming cold pages
+helps saving memory and reducing latency spikes that incurred by the direct
+reclaim of the process or CPU consumption of kswapd, while incurring only
+minimal performance degradation [1]_ [2]_ .
+
+Free Pages Reporting [3]_ based memory over-commit virtualization systems are
+good example of the cases.  In such systems, the guest VMs reports their free
+memory to host, and the host reallocates the reported memory to other guests.
+As a result, the memory of the systems are fully utilized.  However, the
+guests could be not so memory-frugal, mainly because some kernel subsystems and
+user-space applications are designed to use as much memory as available.  Then,
+guests could report only small amount of memory as free to host, results in
+memory utilization drop of the systems.  Running the proactive reclamation in
+guests could mitigate this problem.
+
+How It Works?
+=============
+
+DAMON_RECLAIM finds memory regions that didn't accessed for specific time
+duration and page out.  To avoid it consuming too much CPU for the paging out
+operation, a speed limit can be configured.  Under the speed limit, it pages
+out memory regions that didn't accessed longer time first.  System
+administrators can also configure under what situation this scheme should
+automatically activated and deactivated with three memory pressure watermarks.
+
+Interface: Module Parameters
+============================
+
+To use this feature, you should first ensure your system is running on a kernel
+that is built with ``CONFIG_DAMON_RECLAIM=y``.
+
+To let sysadmins enable or disable it and tune for the given system,
+DAMON_RECLAIM utilizes module parameters.  That is, you can put
+``damon_reclaim.<parameter>=<value>`` on the kernel boot command line or write
+proper values to ``/sys/modules/damon_reclaim/parameters/<parameter>`` files.
+
+Note that the parameter values except ``enabled`` are applied only when
+DAMON_RECLAIM starts.  Therefore, if you want to apply new parameter values in
+runtime and DAMON_RECLAIM is already enabled, you should disable and re-enable
+it via ``enabled`` parameter file.  Writing of the new values to proper
+parameter values should be done before the re-enablement.
+
+Below are the description of each parameter.
+
+enabled
+-------
+
+Enable or disable DAMON_RECLAIM.
+
+You can enable DAMON_RCLAIM by setting the value of this parameter as ``Y``.
+Setting it as ``N`` disables DAMON_RECLAIM.  Note that DAMON_RECLAIM could do
+no real monitoring and reclamation due to the watermarks-based activation
+condition.  Refer to below descriptions for the watermarks parameter for this.
+
+min_age
+-------
+
+Time threshold for cold memory regions identification in microseconds.
+
+If a memory region is not accessed for this or longer time, DAMON_RECLAIM
+identifies the region as cold, and reclaims it.
+
+120 seconds by default.
+
+quota_ms
+--------
+
+Limit of time for the reclamation in milliseconds.
+
+DAMON_RECLAIM tries to use only up to this time within a time window
+(quota_reset_interval_ms) for trying reclamation of cold pages.  This can be
+used for limiting CPU consumption of DAMON_RECLAIM.  If the value is zero, the
+limit is disabled.
+
+10 ms by default.
+
+quota_sz
+--------
+
+Limit of size of memory for the reclamation in bytes.
+
+DAMON_RECLAIM charges amount of memory which it tried to reclaim within a time
+window (quota_reset_interval_ms) and makes no more than this limit is tried.
+This can be used for limiting consumption of CPU and IO.  If this value is
+zero, the limit is disabled.
+
+128 MiB by default.
+
+quota_reset_interval_ms
+-----------------------
+
+The time/size quota charge reset interval in milliseconds.
+
+The charget reset interval for the quota of time (quota_ms) and size
+(quota_sz).  That is, DAMON_RECLAIM does not try reclamation for more than
+quota_ms milliseconds or quota_sz bytes within quota_reset_interval_ms
+milliseconds.
+
+1 second by default.
+
+wmarks_interval
+---------------
+
+Minimal time to wait before checking the watermarks, when DAMON_RECLAIM is
+enabled but inactive due to its watermarks rule.
+
+wmarks_high
+-----------
+
+Free memory rate (per thousand) for the high watermark.
+
+If free memory of the system in bytes per thousand bytes is higher than this,
+DAMON_RECLAIM becomes inactive, so it does nothing but only periodically checks
+the watermarks.
+
+wmarks_mid
+----------
+
+Free memory rate (per thousand) for the middle watermark.
+
+If free memory of the system in bytes per thousand bytes is between this and
+the low watermark, DAMON_RECLAIM becomes active, so starts the monitoring and
+the reclaiming.
+
+wmarks_low
+----------
+
+Free memory rate (per thousand) for the low watermark.
+
+If free memory of the system in bytes per thousand bytes is lower than this,
+DAMON_RECLAIM becomes inactive, so it does nothing but periodically checks the
+watermarks.  In the case, the system falls back to the LRU-list based page
+granularity reclamation logic.
+
+sample_interval
+---------------
+
+Sampling interval for the monitoring in microseconds.
+
+The sampling interval of DAMON for the cold memory monitoring.  Please refer to
+the DAMON documentation (:doc:`usage`) for more detail.
+
+aggr_interval
+-------------
+
+Aggregation interval for the monitoring in microseconds.
+
+The aggregation interval of DAMON for the cold memory monitoring.  Please
+refer to the DAMON documentation (:doc:`usage`) for more detail.
+
+min_nr_regions
+--------------
+
+Minimum number of monitoring regions.
+
+The minimal number of monitoring regions of DAMON for the cold memory
+monitoring.  This can be used to set lower-bound of the monitoring quality.
+But, setting this too high could result in increased monitoring overhead.
+Please refer to the DAMON documentation (:doc:`usage`) for more detail.
+
+max_nr_regions
+--------------
+
+Maximum number of monitoring regions.
+
+The maximum number of monitoring regions of DAMON for the cold memory
+monitoring.  This can be used to set upper-bound of the monitoring overhead.
+However, setting this too low could result in bad monitoring quality.  Please
+refer to the DAMON documentation (:doc:`usage`) for more detail.
+
+monitor_region_start
+--------------------
+
+Start of target memory region in physical address.
+
+The start physical address of memory region that DAMON_RECLAIM will do work
+against.  That is, DAMON_RECLAIM will find cold memory regions in this region
+and reclaims.  By default, biggest System RAM is used as the region.
+
+monitor_region_end
+------------------
+
+End of target memory region in physical address.
+
+The end physical address of memory region that DAMON_RECLAIM will do work
+against.  That is, DAMON_RECLAIM will find cold memory regions in this region
+and reclaims.  By default, biggest System RAM is used as the region.
+
+kdamond_pid
+-----------
+
+PID of the DAMON thread.
+
+If DAMON_RECLAIM is enabled, this becomes the PID of the worker thread.  Else,
+-1.
+
+Example
+=======
+
+Below runtime example commands make DAMON_RECLAIM to find memory regions that
+not accessed for 30 seconds or more and pages out.  The reclamation is limited
+to be done only up to 1 GiB per second to avoid DAMON_RECLAIM consuming too
+much CPU time for the paging out operation.  It also asks DAMON_RECLAIM to do
+nothing if the system's free memory rate is more than 50%, but start the real
+works if it becomes lower than 40%.  If DAMON_RECLAIM doesn't make progress and
+therefore the free memory rate becomes lower than 20%, it asks DAMON_RECLAIM to
+do nothing again, so that we can fall back to the LRU-list based page
+granularity reclamation. ::
+
+    # cd /sys/modules/damon_reclaim/parameters
+    # echo 30000000 > min_age
+    # echo $((1 * 1024 * 1024 * 1024)) > quota_sz
+    # echo 1000 > quota_reset_interval_ms
+    # echo 500 > wmarks_high
+    # echo 400 > wmarks_mid
+    # echo 200 > wmarks_low
+    # echo Y > enabled
+
+.. [1] https://research.google/pubs/pub48551/
+.. [2] https://lwn.net/Articles/787611/
+.. [3] https://www.kernel.org/doc/html/latest/vm/free_page_reporting.html
-- 
2.17.1

Re: [PATCH 00/15] Introduce DAMON-based Proactive Reclamation

[Oleksandr Natalenko]

Hello.

On úterý 19. října 2021 17:07:16 CET SeongJae Park wrote:
> In short, DAMON_RECLAIM with 50ms/s time quota and regions prioritization on
> v5.15-rc5 Linux kernel with ZRAM swap device achieves 38.58% memory saving
> with only 1.94% runtime overhead.  For this, DAMON_RECLAIM consumes only
> 4.97% of single CPU time.

While it really consumes little CPU time, is it fine for `kdamond.0` to be in a 
D (uninterruptible sleep) state all the time while active, pushing loadavg 
over 1.0?

Thanks.

-- 
Oleksandr Natalenko (post-factum)

Re: [PATCH 00/15] Introduce DAMON-based Proactive Reclamation

[SeongJae Park]

Hello Oleksandr,

On Sun, 21 Nov 2021 23:32:12 +0100 Oleksandr Natalenko <oleksandr@natalenko.name> wrote:

> Hello.
> 
> On úterý 19. října 2021 17:07:16 CET SeongJae Park wrote:
> > In short, DAMON_RECLAIM with 50ms/s time quota and regions prioritization on
> > v5.15-rc5 Linux kernel with ZRAM swap device achieves 38.58% memory saving
> > with only 1.94% runtime overhead.  For this, DAMON_RECLAIM consumes only
> > 4.97% of single CPU time.
> 
> While it really consumes little CPU time, is it fine for `kdamond.0` to be in a 
> D (uninterruptible sleep) state all the time while active, pushing loadavg 
> over 1.0?

Good point, this could confuse some users using loadavg.  I will send a fix for
this soon.


Thanks,
SJ

> 
> Thanks.
> 
> -- 
> Oleksandr Natalenko (post-factum)
>