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Message-ID: <20201215115448.25633-13-sjpark@amazon.com>
Date: Tue, 15 Dec 2020 12:54:45 +0100
From: SeongJae Park <sjpark@...zon.com>
To: <akpm@...ux-foundation.org>
CC: SeongJae Park <sjpark@...zon.de>, <Jonathan.Cameron@...wei.com>,
<aarcange@...hat.com>, <acme@...nel.org>,
<alexander.shishkin@...ux.intel.com>, <amit@...nel.org>,
<benh@...nel.crashing.org>, <brendan.d.gregg@...il.com>,
<brendanhiggins@...gle.com>, <cai@....pw>,
<colin.king@...onical.com>, <corbet@....net>, <david@...hat.com>,
<dwmw@...zon.com>, <elver@...gle.com>, <fan.du@...el.com>,
<foersleo@...zon.de>, <gthelen@...gle.com>, <irogers@...gle.com>,
<jolsa@...hat.com>, <kirill@...temov.name>, <mark.rutland@....com>,
<mgorman@...e.de>, <minchan@...nel.org>, <mingo@...hat.com>,
<namhyung@...nel.org>, <peterz@...radead.org>,
<rdunlap@...radead.org>, <riel@...riel.com>, <rientjes@...gle.com>,
<rostedt@...dmis.org>, <rppt@...nel.org>, <sblbir@...zon.com>,
<shakeelb@...gle.com>, <shuah@...nel.org>, <sj38.park@...il.com>,
<snu@...zon.de>, <vbabka@...e.cz>, <vdavydov.dev@...il.com>,
<yang.shi@...ux.alibaba.com>, <ying.huang@...el.com>,
<zgf574564920@...il.com>, <linux-damon@...zon.com>,
<linux-mm@...ck.org>, <linux-doc@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: [PATCH v23 12/15] Documentation: Add documents for DAMON
From: SeongJae Park <sjpark@...zon.de>
This commit adds documents for DAMON under
`Documentation/admin-guide/mm/damon/` and `Documentation/vm/damon/`.
Signed-off-by: SeongJae Park <sjpark@...zon.de>
---
Documentation/admin-guide/mm/damon/guide.rst | 157 ++++++++++
Documentation/admin-guide/mm/damon/index.rst | 15 +
Documentation/admin-guide/mm/damon/plans.rst | 29 ++
Documentation/admin-guide/mm/damon/start.rst | 96 ++++++
Documentation/admin-guide/mm/damon/usage.rst | 302 +++++++++++++++++++
Documentation/admin-guide/mm/index.rst | 1 +
Documentation/vm/damon/api.rst | 20 ++
Documentation/vm/damon/design.rst | 166 ++++++++++
Documentation/vm/damon/eval.rst | 227 ++++++++++++++
Documentation/vm/damon/faq.rst | 58 ++++
Documentation/vm/damon/index.rst | 31 ++
Documentation/vm/index.rst | 1 +
12 files changed, 1103 insertions(+)
create mode 100644 Documentation/admin-guide/mm/damon/guide.rst
create mode 100644 Documentation/admin-guide/mm/damon/index.rst
create mode 100644 Documentation/admin-guide/mm/damon/plans.rst
create mode 100644 Documentation/admin-guide/mm/damon/start.rst
create mode 100644 Documentation/admin-guide/mm/damon/usage.rst
create mode 100644 Documentation/vm/damon/api.rst
create mode 100644 Documentation/vm/damon/design.rst
create mode 100644 Documentation/vm/damon/eval.rst
create mode 100644 Documentation/vm/damon/faq.rst
create mode 100644 Documentation/vm/damon/index.rst
diff --git a/Documentation/admin-guide/mm/damon/guide.rst b/Documentation/admin-guide/mm/damon/guide.rst
new file mode 100644
index 000000000000..c51fb843efaa
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/guide.rst
@@ -0,0 +1,157 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+Optimization Guide
+==================
+
+This document helps you estimating the amount of benefit that you could get
+from DAMON-based optimizations, and describes how you could achieve it. You
+are assumed to already read :doc:`start`.
+
+
+Check The Signs
+===============
+
+No optimization can provide same extent of benefit to every case. Therefore
+you should first guess how much improvements you could get using DAMON. If
+some of below conditions match your situation, you could consider using DAMON.
+
+- *Low IPC and High Cache Miss Ratios.* Low IPC means most of the CPU time is
+ spent waiting for the completion of time-consuming operations such as memory
+ access, while high cache miss ratios mean the caches don't help it well.
+ DAMON is not for cache level optimization, but DRAM level. However,
+ improving DRAM management will also help this case by reducing the memory
+ operation latency.
+- *Memory Over-commitment and Unknown Users.* If you are doing memory
+ overcommitment and you cannot control every user of your system, a memory
+ bank run could happen at any time. You can estimate when it will happen
+ based on DAMON's monitoring results and act earlier to avoid or deal better
+ with the crisis.
+- *Frequent Memory Pressure.* Frequent memory pressure means your system has
+ wrong configurations or memory hogs. DAMON will help you find the right
+ configuration and/or the criminals.
+- *Heterogeneous Memory System.* If your system is utilizing memory devices
+ that placed between DRAM and traditional hard disks, such as non-volatile
+ memory or fast SSDs, DAMON could help you utilizing the devices more
+ efficiently.
+
+
+Profile
+=======
+
+If you found some positive signals, you could start by profiling your workloads
+using DAMON. Find major workloads on your systems and analyze their data
+access pattern to find something wrong or can be improved. The DAMON user
+space tool (``damo``) will be useful for this.
+
+We recommend you to start from working set size distribution check using ``damo
+report wss``. If the distribution is ununiform or quite different from what
+you estimated, you could consider `Memory Configuration`_ optimization.
+
+Then, review the overall access pattern in heatmap form using ``damo report
+heats``. If it shows a simple pattern consists of a small number of memory
+regions having high contrast of access temperature, you could consider manual
+`Program Modification`_.
+
+If you still want to absorb more benefits, you should develop `Personalized
+DAMON Application`_ for your special case.
+
+You don't need to take only one approach among the above plans, but you could
+use multiple of the above approaches to maximize the benefit.
+
+
+Optimize
+========
+
+If the profiling result also says it's worth trying some optimization, you
+could consider below approaches. Note that some of the below approaches assume
+that your systems are configured with swap devices or other types of auxiliary
+memory so that you don't strictly required to accommodate the whole working set
+in the main memory. Most of the detailed optimization should be made on your
+concrete understanding of your memory devices.
+
+
+Memory Configuration
+--------------------
+
+No more no less, DRAM should be large enough to accommodate only important
+working sets, because DRAM is highly performance critical but expensive and
+heavily consumes the power. However, knowing the size of the real important
+working sets is difficult. As a consequence, people usually equips
+unnecessarily large or too small DRAM. Many problems stem from such wrong
+configurations.
+
+Using the working set size distribution report provided by ``damo report wss``,
+you can know the appropriate DRAM size for you. For example, roughly speaking,
+if you worry about only 95 percentile latency, you don't need to equip DRAM of
+a size larger than 95 percentile working set size.
+
+Let's see a real example. This `page
+<https://damonitor.github.io/doc/html/v17/admin-guide/mm/damon/guide.html#memory-configuration>`_
+shows the heatmap and the working set size distributions/changes of
+``freqmine`` workload in PARSEC3 benchmark suite. The working set size spikes
+up to 180 MiB, but keeps smaller than 50 MiB for more than 95% of the time.
+Even though you give only 50 MiB of memory space to the workload, it will work
+well for 95% of the time. Meanwhile, you can save the 130 MiB of memory space.
+
+
+Program Modification
+--------------------
+
+If the data access pattern heatmap plotted by ``damo report heats`` is quite
+simple so that you can understand how the things are going in the workload with
+your human eye, you could manually optimize the memory management.
+
+For example, suppose that the workload has two big memory object but only one
+object is frequently accessed while the other one is only occasionally
+accessed. Then, you could modify the program source code to keep the hot
+object in the main memory by invoking ``mlock()`` or ``madvise()`` with
+``MADV_WILLNEED``. Or, you could proactively evict the cold object using
+``madvise()`` with ``MADV_COLD`` or ``MADV_PAGEOUT``. Using both together
+would be also worthy.
+
+A research work [1]_ using the ``mlock()`` achieved up to 2.55x performance
+speedup.
+
+Let's see another realistic example access pattern for this kind of
+optimizations. This `page
+<https://damonitor.github.io/doc/html/v17/admin-guide/mm/damon/guide.html#program-modification>`_
+shows the visualized access patterns of streamcluster workload in PARSEC3
+benchmark suite. We can easily identify the 100 MiB sized hot object.
+
+
+Personalized DAMON Application
+------------------------------
+
+Above approaches will work well for many general cases, but would not enough
+for some special cases.
+
+If this is the case, it might be the time to forget the comfortable use of the
+user space tool and dive into the debugfs interface (refer to :doc:`usage` for
+the detail) of DAMON. Using the interface, you can control the DAMON more
+flexibly. Therefore, you can write your personalized DAMON application that
+controls the monitoring via the debugfs interface, analyzes the result, and
+applies complex optimizations itself. Using this, you can make more creative
+and wise optimizations.
+
+If you are a kernel space programmer, writing kernel space DAMON applications
+using the API (refer to the :doc:`/vm/damon/api` for more detail) would be an
+option.
+
+
+Reference Practices
+===================
+
+Referencing previously done successful practices could help you getting the
+sense for this kind of optimizations. There is an academic paper [1]_
+reporting the visualized access pattern and manual `Program
+Modification`_ results for a number of realistic workloads. You can also get
+the visualized access patterns [3]_ [4]_ [5]_ and automated DAMON-based memory
+operations results for other realistic workloads that collected with latest
+version of DAMON [2]_ .
+
+.. [1] https://dl.acm.org/doi/10.1145/3366626.3368125
+.. [2] https://damonitor.github.io/test/result/perf/latest/html/
+.. [3] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.1.png.html
+.. [4] https://damonitor.github.io/test/result/visual/latest/rec.wss_sz.png.html
+.. [5] https://damonitor.github.io/test/result/visual/latest/rec.wss_time.png.html
diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst
new file mode 100644
index 000000000000..0baae7a5402b
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/index.rst
@@ -0,0 +1,15 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Monitoring Data Accesses
+========================
+
+:doc:`DAMON </vm/damon/index>` allows light-weight data access monitoring.
+Using this, users can analyze and optimize their systems.
+
+.. toctree::
+ :maxdepth: 2
+
+ start
+ guide
+ usage
diff --git a/Documentation/admin-guide/mm/damon/plans.rst b/Documentation/admin-guide/mm/damon/plans.rst
new file mode 100644
index 000000000000..e3aa5ab96c29
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/plans.rst
@@ -0,0 +1,29 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+Future Plans
+============
+
+DAMON is still on its first stage. Below plans are still under development.
+
+
+Automate Data Access Monitoring-based Memory Operation Schemes Execution
+========================================================================
+
+The ultimate goal of DAMON is to be used as a building block for the data
+access pattern aware kernel memory management optimization. It will make
+system just works efficiently. However, some users having very special
+workloads will want to further do their own optimization. DAMON will automate
+most of the tasks for such manual optimizations in near future. Users will be
+required to only describe what kind of data access pattern-based operation
+schemes they want in a simple form.
+
+By applying a very simple scheme for THP promotion/demotion with a prototype
+implementation, DAMON reduced 60% of THP memory footprint overhead while
+preserving 50% of the THP performance benefit. The detailed results can be
+seen on an external web page [1]_.
+
+Several RFC patchsets for this plan are available [2]_.
+
+.. [1] https://damonitor.github.io/test/result/perf/latest/html/
+.. [2] https://lore.kernel.org/linux-mm/20200616073828.16509-1-sjpark@amazon.com/
diff --git a/Documentation/admin-guide/mm/damon/start.rst b/Documentation/admin-guide/mm/damon/start.rst
new file mode 100644
index 000000000000..deed2ea2321e
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/start.rst
@@ -0,0 +1,96 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Getting Started
+===============
+
+This document briefly describes how you can use DAMON by demonstrating its
+default user space tool. Please note that this document describes only a part
+of its features for brevity. Please refer to :doc:`usage` for more details.
+
+
+TL; DR
+======
+
+Follow below 5 commands to monitor and visualize the access pattern of your
+workload. ::
+
+ $ git clone https://github.com/sjp38/linux -b damon/master
+ /* build the kernel with CONFIG_DAMON=y, install, reboot */
+ $ mount -t debugfs none /sys/kernel/debug/
+ $ cd linux/tools/damon
+ $ ./damo record $(pidof <your workload>)
+ $ ./damo report heats --heatmap access_pattern.png
+
+
+Prerequisites
+=============
+
+Kernel
+------
+
+You should first ensure your system is running on a kernel built with
+``CONFIG_DAMON=y``.
+
+
+User Space Tool
+---------------
+
+For the demonstration, we will use the default user space tool for DAMON,
+called DAMON Operator (DAMO). It is located at ``tools/damon/damo`` of the
+kernel source tree. For brevity, below examples assume you set ``$PATH`` to
+point it. It's not mandatory, though.
+
+Because DAMO is using the debugfs interface (refer to :doc:`usage` for the
+detail) of DAMON, you should ensure debugfs is mounted. Mount it manually as
+below::
+
+ # mount -t debugfs none /sys/kernel/debug/
+
+or append below line to your ``/etc/fstab`` file so that your system can
+automatically mount debugfs from next booting::
+
+ debugfs /sys/kernel/debug debugfs defaults 0 0
+
+
+Recording Data Access Patterns
+==============================
+
+Below commands record memory access pattern of a program and save the
+monitoring results in a file. ::
+
+ $ git clone https://github.com/sjp38/masim
+ $ cd masim; make; ./masim ./configs/zigzag.cfg &
+ $ sudo damo record -o damon.data $(pidof masim)
+
+The first two lines of the commands get an artificial memory access generator
+program and runs it in the background. It will repeatedly access two 100 MiB
+sized memory regions one by one. You can substitute this with your real
+workload. The last line asks ``damo`` to record the access pattern in
+``damon.data`` file.
+
+
+Visualizing Recorded Patterns
+=============================
+
+Below three commands visualize the recorded access patterns into three
+image files. ::
+
+ $ damo report heats --heatmap access_pattern_heatmap.png
+ $ damo report wss --range 0 101 1 --plot wss_dist.png
+ $ damo report wss --range 0 101 1 --sortby time --plot wss_chron_change.png
+
+- ``access_pattern_heatmap.png`` will show the data access pattern in a
+ heatmap, which shows when (x-axis) what memory region (y-axis) is how
+ frequently accessed (color).
+- ``wss_dist.png`` will show the distribution of the working set size.
+- ``wss_chron_change.png`` will show how the working set size has
+ chronologically changed.
+
+You can show the images in a web page [1]_ . Those made with other realistic
+workloads are also available [2]_ [3]_ [4]_.
+
+.. [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
+.. [4] https://damonitor.github.io/test/result/visual/latest/rec.wss_time.png.html
diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
new file mode 100644
index 000000000000..a6606d27a559
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -0,0 +1,302 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Detailed Usages
+===============
+
+DAMON provides below three interfaces for different users.
+
+- *DAMON user space tool.*
+ This is for privileged people such as system administrators who want a
+ just-working human-friendly interface. Using this, users can use the DAMON’s
+ major features in a human-friendly way. It may not be highly tuned for
+ special cases, though. It supports only virtual address spaces monitoring.
+- *debugfs interface.*
+ This is for privileged user space programmers who want more optimized use of
+ DAMON. Using this, users can use DAMON’s major features by reading
+ from and writing to special debugfs files. Therefore, you can write and use
+ your personalized DAMON debugfs wrapper programs that reads/writes the
+ debugfs files instead of you. The DAMON user space tool is also a reference
+ implementation of such programs. It supports only virtual address spaces
+ monitoring.
+- *Kernel Space Programming Interface.*
+ This is for kernel space programmers. Using this, users can utilize every
+ feature of DAMON most flexibly and efficiently by writing kernel space
+ DAMON application programs for you. You can even extend DAMON for various
+ address spaces.
+
+This document does not describe the kernel space programming interface in
+detail. For that, please refer to the :doc:`/vm/damon/api`.
+
+
+DAMON User Space Tool
+=====================
+
+A reference implementation of the DAMON user space tools which provides a
+convenient user interface is in the kernel source tree. It is located at
+``tools/damon/damo`` of the tree.
+
+The tool provides a subcommands based interface. Every subcommand provides
+``-h`` option, which provides the minimal usage of it. Currently, the tool
+supports two subcommands, ``record`` and ``report``.
+
+Below example commands assume you set ``$PATH`` to point ``tools/damon/`` for
+brevity. It is not mandatory for use of ``damo``, though.
+
+
+Recording Data Access Pattern
+-----------------------------
+
+The ``record`` subcommand records the data access pattern of target workloads
+in a file (``./damon.data`` by default). You can specify the target with 1)
+the command for execution of the monitoring target process, or 2) pid of
+running target process. Below example shows a command target usage::
+
+ # cd <kernel>/tools/damon/
+ # damo record "sleep 5"
+
+The tool will execute ``sleep 5`` by itself and record the data access patterns
+of the process. Below example shows a pid target usage::
+
+ # sleep 5 &
+ # damo record `pidof sleep`
+
+The location of the recorded file can be explicitly set using ``-o`` option.
+You can further tune this by setting the monitoring attributes. To know about
+the monitoring attributes in detail, please refer to the
+:doc:`/vm/damon/design`.
+
+
+Analyzing Data Access Pattern
+-----------------------------
+
+The ``report`` subcommand reads a data access pattern record file (if not
+explicitly specified using ``-i`` option, reads ``./damon.data`` file by
+default) and generates human-readable reports. You can specify what type of
+report you want using a sub-subcommand to ``report`` subcommand. ``raw``,
+``heats``, and ``wss`` report types are supported for now.
+
+
+raw
+~~~
+
+``raw`` sub-subcommand simply transforms the binary record into a
+human-readable text. For example::
+
+ $ damo report raw
+ start_time: 193485829398
+ rel time: 0
+ nr_tasks: 1
+ target_id: 1348
+ nr_regions: 4
+ 560189609000-56018abce000( 22827008): 0
+ 7fbdff59a000-7fbdffaf1a00( 5601792): 0
+ 7fbdffaf1a00-7fbdffbb5000( 800256): 1
+ 7ffea0dc0000-7ffea0dfd000( 249856): 0
+
+ rel time: 100000731
+ nr_tasks: 1
+ target_id: 1348
+ nr_regions: 6
+ 560189609000-56018abce000( 22827008): 0
+ 7fbdff59a000-7fbdff8ce933( 3361075): 0
+ 7fbdff8ce933-7fbdffaf1a00( 2240717): 1
+ 7fbdffaf1a00-7fbdffb66d99( 480153): 0
+ 7fbdffb66d99-7fbdffbb5000( 320103): 1
+ 7ffea0dc0000-7ffea0dfd000( 249856): 0
+
+The first line shows the recording started timestamp (nanosecond). Records of
+data access patterns follows. Each record is separated by a blank line. Each
+record first specifies the recorded time (``rel time``) in relative to the
+start time, the number of monitored tasks in this record (``nr_tasks``).
+Recorded data access patterns of each task follow. Each data access pattern
+for each task shows the target's pid (``target_id``) and a number of monitored
+address regions in this access pattern (``nr_regions``) first. After that,
+each line shows the start/end address, size, and the number of observed
+accesses of each region.
+
+
+heats
+~~~~~
+
+The ``raw`` output is very detailed but hard to manually read. ``heats``
+sub-subcommand plots the data in 3-dimensional form, which represents the time
+in x-axis, address of regions in y-axis, and the access frequency in z-axis.
+Users can set the resolution of the map (``--tres`` and ``--ares``) and
+start/end point of each axis (``--tmin``, ``--tmax``, ``--amin``, and
+``--amax``) via optional arguments. For example::
+
+ $ damo report heats --tres 3 --ares 3
+ 0 0 0.0
+ 0 7609002 0.0
+ 0 15218004 0.0
+ 66112620851 0 0.0
+ 66112620851 7609002 0.0
+ 66112620851 15218004 0.0
+ 132225241702 0 0.0
+ 132225241702 7609002 0.0
+ 132225241702 15218004 0.0
+
+This command shows a recorded access pattern in heatmap of 3x3 resolution.
+Therefore it shows 9 data points in total. Each line shows each of the data
+points. The three numbers in each line represent time in nanosecond, address,
+and the observed access frequency.
+
+Users will be able to convert this text output into a heatmap image (represents
+z-axis values with colors) or other 3D representations using various tools such
+as 'gnuplot'. For more convenience, ``heats`` sub-subcommand provides the
+'gnuplot' based heatmap image creation. For this, you can use ``--heatmap``
+option. Also, note that because it uses 'gnuplot' internally, it will fail if
+'gnuplot' is not installed on your system. For example::
+
+ $ ./damo report heats --heatmap heatmap.png
+
+Creates the heatmap image in ``heatmap.png`` file. It supports ``pdf``,
+``png``, ``jpeg``, and ``svg``.
+
+If the target address space is virtual memory address space and you plot the
+entire address space, the huge unmapped regions will make the picture looks
+only black. Therefore you should do proper zoom in / zoom out using the
+resolution and axis boundary-setting arguments. To make this effort minimal,
+you can use ``--guide`` option as below::
+
+ $ ./damo report heats --guide
+ target_id:1348
+ time: 193485829398-198337863555 (4852034157)
+ region 0: 00000094564599762944-00000094564622589952 (22827008)
+ region 1: 00000140454009610240-00000140454016012288 (6402048)
+ region 2: 00000140731597193216-00000140731597443072 (249856)
+
+The output shows unions of monitored regions (start and end addresses in byte)
+and the union of monitored time duration (start and end time in nanoseconds) of
+each target task. Therefore, it would be wise to plot the data points in each
+union. If no axis boundary option is given, it will automatically find the
+biggest union in ``--guide`` output and set the boundary in it.
+
+
+wss
+~~~
+
+The ``wss`` type extracts the distribution and chronological working set size
+changes from the records. For example::
+
+ $ ./damo report wss
+ # <percentile> <wss>
+ # target_id 1348
+ # avr: 66228
+ 0 0
+ 25 0
+ 50 0
+ 75 0
+ 100 1920615
+
+Without any option, it shows the distribution of the working set sizes as
+above. It shows 0th, 25th, 50th, 75th, and 100th percentile and the average of
+the measured working set sizes in the access pattern records. In this case,
+the working set size was zero for 75th percentile but 1,920,615 bytes in max
+and 66,228 bytes on average.
+
+By setting the sort key of the percentile using '--sortby', you can show how
+the working set size has chronologically changed. For example::
+
+ $ ./damo report wss --sortby time
+ # <percentile> <wss>
+ # target_id 1348
+ # avr: 66228
+ 0 0
+ 25 0
+ 50 0
+ 75 0
+ 100 0
+
+The average is still 66,228. And, because the access was spiked in very short
+duration and this command plots only 4 data points, we cannot show when the
+access spikes made. Users can specify the resolution of the distribution
+(``--range``). By giving more fine resolution, the short duration spikes could
+be found.
+
+Similar to that of ``heats --heatmap``, it also supports 'gnuplot' based simple
+visualization of the distribution via ``--plot`` option.
+
+
+debugfs Interface
+=================
+
+DAMON exports four files, ``attrs``, ``target_ids``, ``record``, and
+``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.
+
+
+Attributes
+----------
+
+Users can get and set the ``sampling interval``, ``aggregation interval``,
+``regions update interval``, and min/max number of monitoring target regions by
+reading from and writing to the ``attrs`` file. To know about the monitoring
+attributes in detail, please refer to the :doc:`/vm/damon/design`. For
+example, below commands set those values to 5 ms, 100 ms, 1,000 ms, 10 and
+1000, and then check it again::
+
+ # cd <debugfs>/damon
+ # echo 5000 100000 1000000 10 1000 > attrs
+ # cat attrs
+ 5000 100000 1000000 10 1000
+
+
+Target IDs
+----------
+
+Some types of address spaces supports multiple monitoring target. For example,
+the virtual memory address spaces monitoring can have multiple processes as the
+monitoring targets. Users can set the targets by writing relevant id values of
+the targets to, and get the ids of the current targets by reading from the
+``target_ids`` file. In case of the virtual address spaces monitoring, the
+values should be pids of the monitoring target processes. For example, below
+commands set processes having pids 42 and 4242 as the monitoring targets and
+check it again::
+
+ # cd <debugfs>/damon
+ # echo 42 4242 > target_ids
+ # cat target_ids
+ 42 4242
+
+Note that setting the target ids doesn't start the monitoring.
+
+
+Record
+------
+
+This debugfs file allows you to record monitored access patterns in a regular
+binary file. The recorded results are first written in an in-memory buffer and
+flushed to a file in batch. Users can get and set the size of the buffer and
+the path to the result file by reading from and writing to the ``record`` file.
+For example, below commands set the buffer to be 4 KiB and the result to be
+saved in ``/damon.data``. ::
+
+ # cd <debugfs>/damon
+ # echo "4096 /damon.data" > record
+ # cat record
+ 4096 /damon.data
+
+The recording can be disabled by setting the buffer size zero.
+
+
+Turning On/Off
+--------------
+
+Setting the files as described above doesn't incur effect unless you explicitly
+start the monitoring. You can start, stop, and check the current status of the
+monitoring by writing to and reading from the ``monitor_on`` file. Writing
+``on`` to the file starts the monitoring of the targets with the attributes.
+Writing ``off`` to the file stops those. DAMON also stops if every target
+process is terminated. Below example commands turn on, off, and check the
+status of DAMON::
+
+ # cd <debugfs>/damon
+ # echo on > monitor_on
+ # echo off > monitor_on
+ # cat monitor_on
+ off
+
+Please note that you cannot write to the above-mentioned debugfs files while
+the monitoring is turned on. If you write to the files while DAMON is running,
+an error code such as ``-EBUSY`` will be returned.
diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index cd727cfc1b04..32c27fbf1913 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -27,6 +27,7 @@ the Linux memory management.
concepts
cma_debugfs
+ damon/index
hugetlbpage
idle_page_tracking
ksm
diff --git a/Documentation/vm/damon/api.rst b/Documentation/vm/damon/api.rst
new file mode 100644
index 000000000000..08f34df45523
--- /dev/null
+++ b/Documentation/vm/damon/api.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+API Reference
+=============
+
+Kernel space programs can use every feature of DAMON using below APIs. All you
+need to do is including ``damon.h``, which is located in ``include/linux/`` of
+the source tree.
+
+Structures
+==========
+
+.. kernel-doc:: include/linux/damon.h
+
+
+Functions
+=========
+
+.. kernel-doc:: mm/damon/core.c
diff --git a/Documentation/vm/damon/design.rst b/Documentation/vm/damon/design.rst
new file mode 100644
index 000000000000..727d72093f8f
--- /dev/null
+++ b/Documentation/vm/damon/design.rst
@@ -0,0 +1,166 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======
+Design
+======
+
+Configurable Layers
+===================
+
+DAMON provides data access monitoring functionality while making the accuracy
+and the overhead controllable. The fundamental access monitorings require
+primitives that dependent on and optimized for the target address space. On
+the other hand, the accuracy and overhead tradeoff mechanism, which is the core
+of DAMON, is in the pure logic space. DAMON separates the two parts in
+different layers and defines its interface to allow various low level
+primitives implementations configurable with the core logic.
+
+Due to this separated design and the configurable interface, users can extend
+DAMON for any address space by configuring the core logics with appropriate low
+level primitive implementations. If appropriate one is not provided, users can
+implement the primitives on their own.
+
+For example, physical memory, virtual memory, swap space, those for specific
+processes, NUMA nodes, files, and backing memory devices would be supportable.
+Also, if some architectures or devices support special optimized access check
+primitives, those will be easily configurable.
+
+
+Reference Implementations of Address Space Specific Primitives
+==============================================================
+
+The low level primitives for the fundamental access monitoring are defined in
+two parts:
+
+1. Identification of the monitoring target address range for the address space.
+2. Access check of specific address range in the target space.
+
+DAMON currently provides the implementation of the primitives for only the
+virtual address spaces. Below two subsections describe how it works.
+
+
+PTE Accessed-bit Based Access Check
+-----------------------------------
+
+The implementation for the virtual address space uses PTE Accessed-bit for
+basic access checks. It finds the relevant PTE Accessed bit from the address
+by walking the page table for the target task of the address. In this way, the
+implementation finds and clears the bit for next sampling target address and
+checks whether the bit set again after one sampling period. This could disturb
+other kernel subsystems using the Accessed bits, namely Idle page tracking and
+the reclaim logic. To avoid such disturbances, DAMON makes it mutually
+exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` page
+flags to solve the conflict with the reclaim logic, as Idle page tracking does.
+
+
+VMA-based Target Address Range Construction
+-------------------------------------------
+
+Only small parts in the super-huge virtual address space of the processes are
+mapped to the physical memory and accessed. Thus, tracking the unmapped
+address regions is just wasteful. However, because DAMON can deal with some
+level of noise using the adaptive regions adjustment mechanism, tracking every
+mapping is not strictly required but could even incur a high overhead in some
+cases. That said, too huge unmapped areas inside the monitoring target should
+be removed to not take the time for the adaptive mechanism.
+
+For the reason, this implementation converts the complex mappings to three
+distinct regions that cover every mapped area of the address space. The two
+gaps between the three regions are the two biggest unmapped areas in the given
+address space. The two biggest unmapped areas would be the gap between the
+heap and the uppermost mmap()-ed region, and the gap between the lowermost
+mmap()-ed region and the stack in most of the cases. Because these gaps are
+exceptionally huge in usual address spaces, excluding these will be sufficient
+to make a reasonable trade-off. Below shows this in detail::
+
+ <heap>
+ <BIG UNMAPPED REGION 1>
+ <uppermost mmap()-ed region>
+ (small mmap()-ed regions and munmap()-ed regions)
+ <lowermost mmap()-ed region>
+ <BIG UNMAPPED REGION 2>
+ <stack>
+
+
+Address Space Independent Core Mechanisms
+=========================================
+
+Below four sections describe each of the DAMON core mechanisms and the five
+monitoring attributes, ``sampling interval``, ``aggregation interval``,
+``regions update interval``, ``minimum number of regions``, and ``maximum
+number of regions``.
+
+
+Access Frequency Monitoring
+---------------------------
+
+The output of DAMON says what pages are how frequently accessed for a given
+duration. The resolution of the access frequency is controlled by setting
+``sampling interval`` and ``aggregation interval``. In detail, DAMON checks
+access to each page per ``sampling interval`` and aggregates the results. In
+other words, counts the number of the accesses to each page. After each
+``aggregation interval`` passes, DAMON calls callback functions that previously
+registered by users so that users can read the aggregated results and then
+clears the results. This can be described in below simple pseudo-code::
+
+ while monitoring_on:
+ for page in monitoring_target:
+ if accessed(page):
+ nr_accesses[page] += 1
+ if time() % aggregation_interval == 0:
+ for callback in user_registered_callbacks:
+ callback(monitoring_target, nr_accesses)
+ for page in monitoring_target:
+ nr_accesses[page] = 0
+ sleep(sampling interval)
+
+The monitoring overhead of this mechanism will arbitrarily increase as the
+size of the target workload grows.
+
+
+Region Based Sampling
+---------------------
+
+To avoid the unbounded increase of the overhead, DAMON groups adjacent pages
+that assumed to have the same access frequencies into a region. As long as the
+assumption (pages in a region have the same access frequencies) is kept, only
+one page in the region is required to be checked. Thus, for each ``sampling
+interval``, DAMON randomly picks one page in each region, waits for one
+``sampling interval``, checks whether the page is accessed meanwhile, and
+increases the access frequency of the region if so. Therefore, the monitoring
+overhead is controllable by setting the number of regions. DAMON allows users
+to set the minimum and the maximum number of regions for the trade-off.
+
+This scheme, however, cannot preserve the quality of the output if the
+assumption is not guaranteed.
+
+
+Adaptive Regions Adjustment
+---------------------------
+
+Even somehow the initial monitoring target regions are well constructed to
+fulfill the assumption (pages in same region have similar access frequencies),
+the data access pattern can be dynamically changed. This will result in low
+monitoring quality. To keep the assumption as much as possible, DAMON
+adaptively merges and splits each region based on their access frequency.
+
+For each ``aggregation interval``, it compares the access frequencies of
+adjacent regions and merges those if the frequency difference is small. Then,
+after it reports and clears the aggregated access frequency of each region, it
+splits each region into two or three regions if the total number of regions
+will not exceed the user-specified maximum number of regions after the split.
+
+In this way, DAMON provides its best-effort quality and minimal overhead while
+keeping the bounds users set for their trade-off.
+
+
+Dynamic Target Space Updates Handling
+-------------------------------------
+
+The monitoring target address range could dynamically changed. For example,
+virtual memory could be dynamically mapped and unmapped. Physical memory could
+be hot-plugged.
+
+As the changes could be quite frequent in some cases, DAMON checks the dynamic
+memory mapping changes and applies it to the abstracted target area only for
+each of a user-specified time interval (``regions update interval``).
diff --git a/Documentation/vm/damon/eval.rst b/Documentation/vm/damon/eval.rst
new file mode 100644
index 000000000000..ca97e6334aa7
--- /dev/null
+++ b/Documentation/vm/damon/eval.rst
@@ -0,0 +1,227 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========
+Evaluation
+==========
+
+DAMON is lightweight. It increases system memory usage by 0.42% and slows
+target workloads down by 0.39%.
+
+DAMON is accurate and useful for memory management optimizations. An
+experimental DAMON-based operation scheme for THP, namely 'ethp', removes
+81.45% of THP memory overheads while preserving 50.09% of THP speedup. Another
+experimental DAMON-based 'proactive reclamation' implementation, namely 'prcl',
+reduces 91.45% of residential sets and 22.91% of system memory footprint while
+incurring only 2.43% runtime overhead in the best case (parsec3/freqmine).
+
+
+Setup
+=====
+
+On QEMU/KVM based virtual machines utilizing 130GB of RAM and 36 vCPUs hosted
+by AWS EC2 i3.metal instances that running a kernel that v21 DAMON patchset is
+applied, I measure runtime and consumed system memory while running various
+realistic workloads with several configurations. From each of PARSEC3 [3]_ and
+SPLASH-2X [4]_ benchmark suites I pick 12 workloads, so I use 24 workloads in
+total. I use another wrapper scripts [5]_ for convenient setup and run of the
+workloads.
+
+
+Measurement
+-----------
+
+For the measurement of the amount of consumed memory in system global scope, I
+drop caches before starting each of the workloads and monitor 'MemFree' in the
+'/proc/meminfo' file. To make results more stable, I repeat the runs 5 times
+and average results.
+
+
+Configurations
+--------------
+
+The configurations I use are as below.
+
+- orig: Linux v5.10 with 'madvise' THP policy
+- rec: 'orig' plus DAMON running with virtual memory access recording
+- prec: 'orig' plus DAMON running with physical memory access recording
+- thp: same with 'orig', but use 'always' THP policy
+- ethp: 'orig' plus a DAMON operation scheme, 'efficient THP'
+- prcl: 'orig' plus a DAMON operation scheme, 'proactive reclaim [6]_'
+
+I use 'rec' for measurement of DAMON overheads to target workloads and system
+memory. 'prec' is for physical memory monitroing and recording. It monitors
+17GB sized 'System RAM' region. The remaining configs including 'thp', 'ethp',
+and 'prcl' are for measurement of DAMON monitoring accuracy.
+
+'ethp' and 'prcl' are simple DAMON-based operation schemes developed for
+proof of concepts of DAMON. 'ethp' reduces memory space waste of THP by using
+DAMON for the decision of promotions and demotion for huge pages, while 'prcl'
+is as similar as the original work. Those are implemented as below::
+
+ # format: <min/max size> <min/max frequency (0-100)> <min/max age> <action>
+ # ethp: Use huge pages if a region shows >=5% access rate, use regular
+ # pages if a region >=2MB shows 0 access rate for >=7 seconds
+ min max 5 max min max hugepage
+ 2M max min min 7s max nohugepage
+
+ # prcl: If a region >=4KB shows 0 access rate for >=5 seconds, page out.
+ 4K max 0 0 5s max pageout
+
+Note that both 'ethp' and 'prcl' are designed with my only straightforward
+intuition because those are for only proof of concepts and monitoring accuracy
+of DAMON. In other words, those are not for production. For production use,
+those should be more tuned.
+
+The evaluation is done using the tests package for DAMON, ``damon-tests`` [7]_.
+Using it, you can do the evaluation and generate a report on your own.
+
+.. [1] "Redis latency problems troubleshooting", https://redis.io/topics/latency
+.. [2] "Disable Transparent Huge Pages (THP)",
+ https://docs.mongodb.com/manual/tutorial/transparent-huge-pages/
+.. [3] "The PARSEC Becnhmark Suite", https://parsec.cs.princeton.edu/index.htm
+.. [4] "SPLASH-2x", https://parsec.cs.princeton.edu/parsec3-doc.htm#splash2x
+.. [5] "parsec3_on_ubuntu", https://github.com/sjp38/parsec3_on_ubuntu
+.. [6] "Proactively reclaiming idle memory", https://lwn.net/Articles/787611/
+.. [7] "damon-tests", https://github.com/awslabs/damon-tests
+
+
+Results
+=======
+
+Below two tables show the measurement results. The runtimes are in seconds
+while the memory usages are in KiB. Each configuration except 'orig' shows
+its overhead relative to 'orig' in percent within parenthesizes.::
+
+ runtime orig rec (overhead) prec (overhead) thp (overhead) ethp (overhead) prcl (overhead)
+ parsec3/blackscholes 138.247 139.131 (0.64) 138.872 (0.45) 138.436 (0.14) 138.599 (0.25) 151.104 (9.30)
+ parsec3/bodytrack 124.338 124.450 (0.09) 124.624 (0.23) 124.357 (0.02) 124.705 (0.29) 125.329 (0.80)
+ parsec3/canneal 211.054 216.642 (2.65) 213.773 (1.29) 176.039 (-16.59) 214.460 (1.61) 249.492 (18.21)
+ parsec3/dedup 18.452 18.218 (-1.27) 18.334 (-0.64) 18.074 (-2.05) 18.315 (-0.74) 20.489 (11.04)
+ parsec3/facesim 347.473 352.724 (1.51) 345.951 (-0.44) 340.480 (-2.01) 344.158 (-0.95) 371.561 (6.93)
+ parsec3/fluidanimate 339.895 337.531 (-0.70) 335.378 (-1.33) 326.410 (-3.97) 333.322 (-1.93) 332.785 (-2.09)
+ parsec3/freqmine 436.827 437.962 (0.26) 439.345 (0.58) 436.844 (0.00) 438.301 (0.34) 447.430 (2.43)
+ parsec3/raytrace 185.539 183.376 (-1.17) 185.962 (0.23) 186.311 (0.42) 184.981 (-0.30) 207.715 (11.95)
+ parsec3/streamcluster 682.926 686.849 (0.57) 677.420 (-0.81) 599.544 (-12.21) 615.506 (-9.87) 789.596 (15.62)
+ parsec3/swaptions 219.616 221.386 (0.81) 221.320 (0.78) 220.269 (0.30) 221.426 (0.82) -100.000 (0.00)
+ parsec3/vips 88.397 88.504 (0.12) 87.550 (-0.96) 87.801 (-0.67) 87.638 (-0.86) 89.135 (0.84)
+ parsec3/x264 113.634 114.143 (0.45) 116.506 (2.53) 112.728 (-0.80) 116.572 (2.59) 114.607 (0.86)
+ splash2x/barnes 130.160 130.475 (0.24) 130.006 (-0.12) 119.679 (-8.05) 128.869 (-0.99) 173.767 (33.50)
+ splash2x/fft 61.243 60.419 (-1.35) 60.144 (-1.79) 46.930 (-23.37) 58.679 (-4.19) 94.651 (54.55)
+ splash2x/lu_cb 132.438 132.733 (0.22) 132.746 (0.23) 131.756 (-0.52) 132.492 (0.04) 146.579 (10.68)
+ splash2x/lu_ncb 151.133 150.656 (-0.32) 151.187 (0.04) 150.106 (-0.68) 149.088 (-1.35) 156.120 (3.30)
+ splash2x/ocean_cp 87.010 88.161 (1.32) 90.317 (3.80) 77.344 (-11.11) 77.739 (-10.65) 113.273 (30.18)
+ splash2x/ocean_ncp 161.819 160.428 (-0.86) 161.508 (-0.19) 117.250 (-27.54) 141.303 (-12.68) 279.021 (72.43)
+ splash2x/radiosity 144.159 142.662 (-1.04) 145.874 (1.19) 141.937 (-1.54) 142.184 (-1.37) 151.460 (5.06)
+ splash2x/radix 51.341 51.156 (-0.36) 51.601 (0.51) 46.678 (-9.08) 49.119 (-4.33) 82.058 (59.83)
+ splash2x/raytrace 133.543 134.201 (0.49) 134.022 (0.36) 132.010 (-1.15) 133.065 (-0.36) 141.626 (6.05)
+ splash2x/volrend 120.229 120.489 (0.22) 121.690 (1.22) 119.702 (-0.44) 119.693 (-0.45) 122.247 (1.68)
+ splash2x/water_nsquared 371.382 375.238 (1.04) 373.726 (0.63) 355.410 (-4.30) 358.243 (-3.54) 403.058 (8.53)
+ splash2x/water_spatial 133.738 134.831 (0.82) 133.865 (0.10) 133.270 (-0.35) 133.320 (-0.31) 152.743 (14.21)
+ total 4584.600 4602.380 (0.39) 4591.740 (0.16) 4339.370 (-5.35) 4461.770 (-2.68) 4915.870 (7.23)
+
+
+ memused.avg orig rec (overhead) prec (overhead) thp (overhead) ethp (overhead) prcl (overhead)
+ parsec3/blackscholes 1822419.200 1832932.800 (0.58) 1825942.600 (0.19) 1817011.600 (-0.30) 1830445.600 (0.44) 1595311.600 (-12.46)
+ parsec3/bodytrack 1424439.600 1437080.200 (0.89) 1438747.200 (1.00) 1423658.600 (-0.05) 1434771.600 (0.73) 1437144.200 (0.89)
+ parsec3/canneal 1036933.000 1054711.800 (1.71) 1050022.200 (1.26) 1032368.400 (-0.44) 1052744.400 (1.52) 1049121.200 (1.18)
+ parsec3/dedup 2500773.600 2502254.800 (0.06) 2467656.000 (-1.32) 2511153.400 (0.42) 2495594.600 (-0.21) 2488489.200 (-0.49)
+ parsec3/facesim 535653.600 550504.000 (2.77) 547305.400 (2.18) 542355.200 (1.25) 552392.400 (3.12) 484499.000 (-9.55)
+ parsec3/fluidanimate 572288.600 585018.400 (2.22) 582106.200 (1.72) 571557.400 (-0.13) 583349.400 (1.93) 493663.400 (-13.74)
+ parsec3/freqmine 982803.000 997657.400 (1.51) 995492.200 (1.29) 986962.000 (0.42) 998352.400 (1.58) 757675.800 (-22.91)
+ parsec3/raytrace 1742834.000 1754262.200 (0.66) 1747630.800 (0.28) 1731301.600 (-0.66) 1749506.400 (0.38) 1543049.400 (-11.46)
+ parsec3/streamcluster 117851.800 158437.400 (34.44) 158582.400 (34.56) 122982.600 (4.35) 135280.200 (14.79) 136526.600 (15.85)
+ parsec3/swaptions 14375.800 28709.600 (99.71) 28302.000 (96.87) 13821.400 (-3.86) 25697.800 (78.76) -100.000 (0.00)
+ parsec3/vips 2982188.400 2998594.600 (0.55) 3004458.800 (0.75) 2981225.200 (-0.03) 2997897.400 (0.53) 2979860.000 (-0.08)
+ parsec3/x264 3241201.800 3250602.600 (0.29) 3257842.600 (0.51) 3238675.800 (-0.08) 3254314.200 (0.40) 3243305.667 (0.06)
+ splash2x/barnes 1202953.000 1212273.400 (0.77) 1199432.200 (-0.29) 1214065.600 (0.92) 1218764.400 (1.31) 881206.000 (-26.75)
+ splash2x/fft 9729496.200 9631956.200 (-1.00) 9282596.600 (-4.59) 9892176.200 (1.67) 9632687.800 (-0.99) 10320735.333 (6.08)
+ splash2x/lu_cb 512464.200 523658.200 (2.18) 515659.200 (0.62) 513609.000 (0.22) 520062.000 (1.48) 338391.667 (-33.97)
+ splash2x/lu_ncb 512790.400 528954.400 (3.15) 521128.600 (1.63) 513166.000 (0.07) 523937.800 (2.17) 426409.333 (-16.85)
+ splash2x/ocean_cp 3342031.600 3326082.400 (-0.48) 3258501.400 (-2.50) 3367646.400 (0.77) 3314408.400 (-0.83) 3181677.000 (-4.80)
+ splash2x/ocean_ncp 3904158.200 3922279.200 (0.46) 3870676.800 (-0.86) 7071312.600 (81.12) 4513390.200 (15.60) 3517213.000 (-9.91)
+ splash2x/radiosity 1460571.200 1463947.200 (0.23) 1454906.200 (-0.39) 1470355.800 (0.67) 1465063.200 (0.31) 450619.333 (-69.15)
+ splash2x/radix 2379050.200 2377324.000 (-0.07) 2270805.200 (-4.55) 2477275.200 (4.13) 2313398.800 (-2.76) 2433462.333 (2.29)
+ splash2x/raytrace 42587.000 55138.400 (29.47) 55933.200 (31.34) 49202.200 (15.53) 59114.400 (38.81) 50805.000 (19.30)
+ splash2x/volrend 149927.000 163164.400 (8.83) 161644.400 (7.82) 149249.000 (-0.45) 160589.600 (7.11) 159004.000 (6.05)
+ splash2x/water_nsquared 39653.400 54180.600 (36.64) 53137.800 (34.01) 42475.000 (7.12) 52911.800 (33.44) 47500.333 (19.79)
+ splash2x/water_spatial 669766.600 681525.600 (1.76) 674610.800 (0.72) 670925.800 (0.17) 679559.000 (1.46) 405725.667 (-39.42)
+ total 40919400.000 41091400.000 (0.42) 40423000.000 (-1.21) 44404600.000 (8.52) 41564259.000 (1.58) 38421300.000 (-6.10)
+
+
+DAMON Overheads
+---------------
+
+In total, DAMON virtual memory access recording feature ('rec') incurs 0.39%
+runtime overhead and 0.42% memory space overhead. Even though the size of the
+monitoring target region becomes much larger with the physical memory access
+recording ('prec'), it still shows only modest amount of overhead (0.16% for
+runtime and -1.21% for memory footprint).
+
+For a convenient test run of 'rec' and 'prec', I use a Python wrapper. The
+wrapper constantly consumes about 10-15MB of memory. This becomes a high
+memory overhead if the target workload has a small memory footprint.
+Nonetheless, the overheads are not from DAMON, but from the wrapper, and thus
+should be ignored. This fake memory overhead continues in 'ethp' and 'prcl',
+as those configurations are also using the Python wrapper.
+
+
+Efficient THP
+-------------
+
+THP 'always' enabled policy achieves 5.35% speedup but incurs 8.52% memory
+overhead. It achieves 27.54% speedup in the best case, but 81.72% memory
+overhead in the worst case. Interestingly, both the best and worst-case are
+with 'splash2x/ocean_ncp').
+
+The 2-lines implementation of data access monitoring based THP version ('ethp')
+shows 2.68% speedup and 1.58% memory overhead. In other words, 'ethp' removes
+81.45% of THP memory waste while preserving 50.09% of THP speedup in total. In
+the case of the 'splash2x/ocean_ncp', 'ethp' removes 80.76% of THP memory waste
+while preserving 46.04% of THP speedup.
+
+
+Proactive Reclamation
+---------------------
+
+As similar to the original work, I use 4G 'zram' swap device for this
+configuration.
+
+In total, our 1 line implementation of Proactive Reclamation, 'prcl', incurred
+7.23% runtime overhead in total while achieving 6.10% system memory footprint
+reduction.
+
+Nonetheless, as the memory usage is calculated with 'MemFree' in
+'/proc/meminfo', it contains the SwapCached pages. As the swapcached pages can
+be easily evicted, I also measured the residential set size of the workloads::
+
+ rss.avg orig rec (overhead) prec (overhead) thp (overhead) ethp (overhead) prcl (overhead)
+ parsec3/blackscholes 585288.600 586175.800 (0.15) 586433.800 (0.20) 587028.600 (0.30) 587996.000 (0.46) 240808.600 (-58.86)
+ parsec3/bodytrack 32139.000 32312.400 (0.54) 32201.800 (0.20) 32357.000 (0.68) 32263.000 (0.39) 18371.000 (-42.84)
+ parsec3/canneal 843125.000 842998.800 (-0.01) 842991.000 (-0.02) 837536.400 (-0.66) 843580.600 (0.05) 825739.000 (-2.06)
+ parsec3/dedup 1187272.400 1175883.400 (-0.96) 1183341.800 (-0.33) 1192656.600 (0.45) 1178204.600 (-0.76) 582322.000 (-50.95)
+ parsec3/facesim 311757.600 311792.200 (0.01) 311751.400 (-0.00) 317679.400 (1.90) 315929.200 (1.34) 187274.800 (-39.93)
+ parsec3/fluidanimate 531844.800 531840.800 (-0.00) 531816.800 (-0.01) 532855.200 (0.19) 532576.400 (0.14) 439993.400 (-17.27)
+ parsec3/freqmine 552634.600 552707.800 (0.01) 552549.600 (-0.02) 555529.400 (0.52) 554548.200 (0.35) 47231.400 (-91.45)
+ parsec3/raytrace 887301.000 883878.400 (-0.39) 884147.800 (-0.36) 874717.000 (-1.42) 881240.200 (-0.68) 264899.000 (-70.15)
+ parsec3/streamcluster 110901.000 110899.200 (-0.00) 110906.200 (0.00) 115357.800 (4.02) 115521.800 (4.17) 109695.400 (-1.09)
+ parsec3/swaptions 5697.800 5682.600 (-0.27) 5704.400 (0.12) 5684.000 (-0.24) 5668.600 (-0.51) -100.000 (0.00)
+ parsec3/vips 32083.400 31877.000 (-0.64) 31873.800 (-0.65) 33041.200 (2.99) 33781.600 (5.29) 28844.667 (-10.09)
+ parsec3/x264 81776.600 81616.600 (-0.20) 81822.800 (0.06) 84827.400 (3.73) 83490.400 (2.10) 81161.333 (-0.75)
+ splash2x/barnes 1219285.200 1218478.600 (-0.07) 1218261.800 (-0.08) 1227469.800 (0.67) 1222605.400 (0.27) 460175.000 (-62.26)
+ splash2x/fft 10080559.600 10000486.200 (-0.79) 9996101.600 (-0.84) 10296965.200 (2.15) 9974327.200 (-1.05) 6932814.000 (-31.23)
+ splash2x/lu_cb 511985.800 511815.600 (-0.03) 511759.600 (-0.04) 511275.800 (-0.14) 511932.400 (-0.01) 319837.000 (-37.53)
+ splash2x/lu_ncb 511416.400 511389.800 (-0.01) 511257.800 (-0.03) 511574.800 (0.03) 511356.400 (-0.01) 412134.333 (-19.41)
+ splash2x/ocean_cp 3424155.800 3421099.600 (-0.09) 3415628.600 (-0.25) 3443500.000 (0.56) 3415558.200 (-0.25) 2436061.333 (-28.86)
+ splash2x/ocean_ncp 3939855.400 3934175.600 (-0.14) 3938673.800 (-0.03) 7177367.200 (82.17) 4581698.000 (16.29) 2391616.000 (-39.30)
+ splash2x/radiosity 1471925.400 1418593.800 (-3.62) 1474347.000 (0.16) 1485447.800 (0.92) 1475442.800 (0.24) 144195.333 (-90.20)
+ splash2x/radix 2465408.000 2484122.000 (0.76) 2449926.000 (-0.63) 2562083.200 (3.92) 2403580.400 (-2.51) 1539977.333 (-37.54)
+ splash2x/raytrace 23279.200 23288.800 (0.04) 23319.200 (0.17) 29137.000 (25.16) 26747.000 (14.90) 13287.667 (-42.92)
+ splash2x/volrend 44203.600 44115.000 (-0.20) 43493.000 (-1.61) 45079.000 (1.98) 45301.000 (2.48) 30139.333 (-31.82)
+ splash2x/water_nsquared 29424.000 29413.600 (-0.04) 29425.600 (0.01) 30163.800 (2.51) 30527.400 (3.75) 22633.667 (-23.08)
+ splash2x/water_spatial 663586.800 664276.200 (0.10) 664012.800 (0.06) 664078.800 (0.07) 663830.800 (0.04) 299712.667 (-54.83)
+ total 29547000.000 29408900.000 (-0.47) 29431800.000 (-0.39) 33153500.000 (12.21) 30027700.000 (1.63) 17828900.000 (-39.66)
+
+In total, 39.66% of residential sets were reduced.
+
+With parsec3/freqmine, 'prcl' reduced 91.45% of residential sets and 22.91% of
+system memory usage while incurring only 2.43% runtime overhead.
diff --git a/Documentation/vm/damon/faq.rst b/Documentation/vm/damon/faq.rst
new file mode 100644
index 000000000000..088128bbf22b
--- /dev/null
+++ b/Documentation/vm/damon/faq.rst
@@ -0,0 +1,58 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Frequently Asked Questions
+==========================
+
+Why a new subsystem, instead of extending perf or other user space tools?
+=========================================================================
+
+First, because it needs to be lightweight as much as possible so that it can be
+used online, any unnecessary overhead such as kernel - user space context
+switching cost should be avoided. Second, DAMON aims to be used by other
+programs including the kernel. Therefore, having a dependency on specific
+tools like perf is not desirable. These are the two biggest reasons why DAMON
+is implemented in the kernel space.
+
+
+Can 'idle pages tracking' or 'perf mem' substitute DAMON?
+=========================================================
+
+Idle page tracking is a low level primitive for access check of the physical
+address space. 'perf mem' is similar, though it can use sampling to minimize
+the overhead. On the other hand, DAMON is a higher-level framework for the
+monitoring of various address spaces. It is focused on memory management
+optimization and provides sophisticated accuracy/overhead handling mechanisms.
+Therefore, 'idle pages tracking' and 'perf mem' could provide a subset of
+DAMON's output, but cannot substitute DAMON.
+
+
+How can I optimize my system's memory management using DAMON?
+=============================================================
+
+Because there are several ways for the DAMON-based optimizations, we wrote a
+separate document, :doc:`/admin-guide/mm/damon/guide`. Please refer to that.
+
+
+Does DAMON support virtual memory only?
+=======================================
+
+No. The core of the DAMON is address space independent. The address space
+specific low level primitive parts including monitoring target regions
+constructions and actual access checks can be implemented and configured on the
+DAMON core by the users. In this way, DAMON users can monitor any address
+space with any access check technique.
+
+Nonetheless, DAMON provides vma tracking and PTE Accessed bit check based
+implementations of the address space dependent functions for the virtual memory
+by default, for a reference and convenient use. In near future, we will
+provide those for physical memory address space.
+
+
+Can I simply monitor page granularity?
+======================================
+
+Yes. You can do so by setting the ``min_nr_regions`` attribute higher than the
+working set size divided by the page size. Because the monitoring target
+regions size is forced to be ``>=page size``, the region split will make no
+effect.
diff --git a/Documentation/vm/damon/index.rst b/Documentation/vm/damon/index.rst
new file mode 100644
index 000000000000..17dca3c12aad
--- /dev/null
+++ b/Documentation/vm/damon/index.rst
@@ -0,0 +1,31 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+DAMON: Data Access MONitor
+==========================
+
+DAMON is a data access monitoring framework subsystem for the Linux kernel.
+The core mechanisms of DAMON (refer to :doc:`design` for the detail) make it
+
+ - *accurate* (the monitoring output is useful enough for DRAM level memory
+ management; It might not appropriate for CPU Cache levels, though),
+ - *light-weight* (the monitoring overhead is low enough to be applied online),
+ and
+ - *scalable* (the upper-bound of the overhead is in constant range regardless
+ of the size of target workloads).
+
+Using this framework, therefore, the kernel's memory management mechanisms can
+make advanced decisions. Experimental memory management optimization works
+that incurring high data accesses monitoring overhead could implemented again.
+In user space, meanwhile, users who have some special workloads can write
+personalized applications for better understanding and optimizations of their
+workloads and systems.
+
+.. toctree::
+ :maxdepth: 2
+
+ faq
+ design
+ eval
+ api
+ plans
diff --git a/Documentation/vm/index.rst b/Documentation/vm/index.rst
index eff5fbd492d0..b51f0d8992f8 100644
--- a/Documentation/vm/index.rst
+++ b/Documentation/vm/index.rst
@@ -32,6 +32,7 @@ descriptions of data structures and algorithms.
arch_pgtable_helpers
balance
cleancache
+ damon/index
free_page_reporting
frontswap
highmem
--
2.17.1
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