From: SeongJae Park <sjpark@xxxxxxxxx> This commit adds documents for DAMON under `Documentation/admin-guide/mm/damon/` and `Documentation/vm/damon/`. Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> --- 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@xxxxxxxxxx/ 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
