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Docs/admin-guide/mm/damon/usage: update for scheme quotas and watermarks
DAMOS features including time/space quota limits and watermarks are not described in the DAMON debugfs interface document. This commit updates the document for the features. Link: https://lkml.kernel.org/r/20211209131806.19317-3-sj@kernel.org Signed-off-by: SeongJae Park <sj@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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SeongJae Park
Linus Torvalds
parent
88f86dcfa4
commit
6322416b2d
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@ -131,24 +131,38 @@ Schemes
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For usual DAMON-based data access aware memory management optimizations, users
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would simply want the system to apply a memory management action to a memory
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region of a specific size having a specific access frequency for a specific
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time. DAMON receives such formalized operation schemes from the user and
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applies those to the target processes. It also counts the total number and
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size of regions that each scheme is applied. This statistics can be used for
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online analysis or tuning of the schemes.
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region of a specific access pattern. DAMON receives such formalized operation
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schemes from the user and applies those to the target processes.
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Users can get and set the schemes by reading from and writing to ``schemes``
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debugfs file. Reading the file also shows the statistics of each scheme. To
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the file, each of the schemes should be represented in each line in below form:
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the file, each of the schemes should be represented in each line in below
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form::
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min-size max-size min-acc max-acc min-age max-age action
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<target access pattern> <action> <quota> <watermarks>
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Note that the ranges are closed interval. Bytes for the size of regions
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(``min-size`` and ``max-size``), number of monitored accesses per aggregate
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interval for access frequency (``min-acc`` and ``max-acc``), number of
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aggregate intervals for the age of regions (``min-age`` and ``max-age``), and a
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predefined integer for memory management actions should be used. The supported
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numbers and their meanings are as below.
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You can disable schemes by simply writing an empty string to the file.
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Target Access Pattern
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~~~~~~~~~~~~~~~~~~~~~
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The ``<target access pattern>`` is constructed with three ranges in below
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form::
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min-size max-size min-acc max-acc min-age max-age
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Specifically, bytes for the size of regions (``min-size`` and ``max-size``),
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number of monitored accesses per aggregate interval for access frequency
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(``min-acc`` and ``max-acc``), number of aggregate intervals for the age of
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regions (``min-age`` and ``max-age``) are specified. Note that the ranges are
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closed interval.
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Action
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~~~~~~
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The ``<action>`` is a predefined integer for memory management actions, which
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DAMON will apply to the regions having the target access pattern. The
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supported numbers and their meanings are as below.
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- 0: Call ``madvise()`` for the region with ``MADV_WILLNEED``
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- 1: Call ``madvise()`` for the region with ``MADV_COLD``
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@ -157,20 +171,79 @@ numbers and their meanings are as below.
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- 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
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- 5: Do nothing but count the statistics
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You can disable schemes by simply writing an empty string to the file. For
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example, below commands applies a scheme saying "If a memory region of size in
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[4KiB, 8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
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interval in [10, 20], page out the region", check the entered scheme again, and
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finally remove the scheme. ::
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Quota
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~~~~~
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Optimal ``target access pattern`` for each ``action`` is workload dependent, so
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not easy to find. Worse yet, setting a scheme of some action too aggressive
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can cause severe overhead. To avoid such overhead, users can limit time and
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size quota for the scheme via the ``<quota>`` in below form::
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<ms> <sz> <reset interval> <priority weights>
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This makes DAMON to try to use only up to ``<ms>`` milliseconds for applying
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the action to memory regions of the ``target access pattern`` within the
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``<reset interval>`` milliseconds, and to apply the action to only up to
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``<sz>`` bytes of memory regions within the ``<reset interval>``. Setting both
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``<ms>`` and ``<sz>`` zero disables the quota limits.
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When the quota limit is expected to be exceeded, DAMON prioritizes found memory
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regions of the ``target access pattern`` based on their size, access frequency,
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and age. For personalized prioritization, users can set the weights for the
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three properties in ``<priority weights>`` in below form::
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<size weight> <access frequency weight> <age weight>
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Watermarks
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~~~~~~~~~~
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Some schemes would need to run based on current value of the system's specific
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metrics like free memory ratio. For such cases, users can specify watermarks
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for the condition.::
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<metric> <check interval> <high mark> <middle mark> <low mark>
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``<metric>`` is a predefined integer for the metric to be checked. The
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supported numbers and their meanings are as below.
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- 0: Ignore the watermarks
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- 1: System's free memory rate (per thousand)
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The value of the metric is checked every ``<check interval>`` microseconds.
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If the value is higher than ``<high mark>`` or lower than ``<low mark>``, the
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scheme is deactivated. If the value is lower than ``<mid mark>``, the scheme
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is activated.
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Statistics
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~~~~~~~~~~
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It also counts the total number and bytes of regions that each scheme is
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applied. This statistics can be used for online analysis or tuning of the
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schemes.
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The statistics can be shown by reading the ``schemes`` file. Reading the file
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will show each scheme you entered in each line, and the two numbers for the
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statistics will be added at the end of each line.
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Example
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~~~~~~~
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Below commands applies a scheme saying "If a memory region of size in [4KiB,
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8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
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interval in [10, 20], page out the region. For the paging out, use only up to
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10ms per second, and also don't page out more than 1GiB per second. Under the
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limitation, page out memory regions having longer age first. Also, check the
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free memory rate of the system every 5 seconds, start the monitoring and paging
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out when the free memory rate becomes lower than 50%, but stop it if the free
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memory rate becomes larger than 60%, or lower than 30%".::
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# cd <debugfs>/damon
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# echo "4096 8192 0 5 10 20 2" > schemes
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# cat schemes
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4096 8192 0 5 10 20 2 0 0
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# echo > schemes
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The last two integers in the 4th line of above example is the total number and
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the total size of the regions that the scheme is applied.
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# scheme="4096 8192 0 5 10 20 2" # target access pattern and action
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# scheme+=" 10 $((1024*1024*1024)) 1000" # quotas
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# scheme+=" 0 0 100" # prioritization weights
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# scheme+=" 1 5000000 600 500 300" # watermarks
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# echo "$scheme" > schemes
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Turning On/Off
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