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Docs/admin-guide/mm/damon/usage: update for scheme quotas and watermarks

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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 2022-01-14 14:10:02 -08:00 committed by Linus Torvalds
parent 88f86dcfa4
commit 6322416b2d
1 changed files with 98 additions and 25 deletions
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123
Documentation/admin-guide/mm/damon/usage.rst
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@ -131,24 +131,38 @@ Schemes
For usual DAMON-based data access aware memory management optimizations, users
would simply want the system to apply a memory management action to a memory
region of a specific size having a specific access frequency for a specific
time. DAMON receives such formalized operation schemes from the user and
applies those to the target processes. It also counts the total number and
size of regions that each scheme is applied. This statistics can be used for
online analysis or tuning of the schemes.
region of a specific access pattern. DAMON receives such formalized operation
schemes from the user and applies those to the target processes.
Users can get and set the schemes by reading from and writing to ``schemes``
debugfs file. Reading the file also shows the statistics of each scheme. To
the file, each of the schemes should be represented in each line in below form:
the file, each of the schemes should be represented in each line in below
form::
min-size max-size min-acc max-acc min-age max-age action
<target access pattern> <action> <quota> <watermarks>
Note that the ranges are closed interval. Bytes for the size of regions
(``min-size`` and ``max-size``), number of monitored accesses per aggregate
interval for access frequency (``min-acc`` and ``max-acc``), number of
aggregate intervals for the age of regions (``min-age`` and ``max-age``), and a
predefined integer for memory management actions should be used. The supported
numbers and their meanings are as below.
You can disable schemes by simply writing an empty string to the file.
Target Access Pattern
~~~~~~~~~~~~~~~~~~~~~
The ``<target access pattern>`` is constructed with three ranges in below
form::
min-size max-size min-acc max-acc min-age max-age
Specifically, bytes for the size of regions (``min-size`` and ``max-size``),
number of monitored accesses per aggregate interval for access frequency
(``min-acc`` and ``max-acc``), number of aggregate intervals for the age of
regions (``min-age`` and ``max-age``) are specified. Note that the ranges are
closed interval.
Action
~~~~~~
The ``<action>`` is a predefined integer for memory management actions, which
DAMON will apply to the regions having the target access pattern. The
supported numbers and their meanings are as below.
- 0: Call ``madvise()`` for the region with ``MADV_WILLNEED``
- 1: Call ``madvise()`` for the region with ``MADV_COLD``
@ -157,20 +171,79 @@ numbers and their meanings are as below.
- 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
- 5: Do nothing but count the statistics
You can disable schemes by simply writing an empty string to the file. For
example, below commands applies a scheme saying "If a memory region of size in
[4KiB, 8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
interval in [10, 20], page out the region", check the entered scheme again, and
finally remove the scheme. ::
Quota
~~~~~
Optimal ``target access pattern`` for each ``action`` is workload dependent, so
not easy to find. Worse yet, setting a scheme of some action too aggressive
can cause severe overhead. To avoid such overhead, users can limit time and
size quota for the scheme via the ``<quota>`` in below form::
<ms> <sz> <reset interval> <priority weights>
This makes DAMON to try to use only up to ``<ms>`` milliseconds for applying
the action to memory regions of the ``target access pattern`` within the
``<reset interval>`` milliseconds, and to apply the action to only up to
``<sz>`` bytes of memory regions within the ``<reset interval>``. Setting both
``<ms>`` and ``<sz>`` zero disables the quota limits.
When the quota limit is expected to be exceeded, DAMON prioritizes found memory
regions of the ``target access pattern`` based on their size, access frequency,
and age. For personalized prioritization, users can set the weights for the
three properties in ``<priority weights>`` in below form::
<size weight> <access frequency weight> <age weight>
Watermarks
~~~~~~~~~~
Some schemes would need to run based on current value of the system's specific
metrics like free memory ratio. For such cases, users can specify watermarks
for the condition.::
<metric> <check interval> <high mark> <middle mark> <low mark>
``<metric>`` is a predefined integer for the metric to be checked. The
supported numbers and their meanings are as below.
- 0: Ignore the watermarks
- 1: System's free memory rate (per thousand)
The value of the metric is checked every ``<check interval>`` microseconds.
If the value is higher than ``<high mark>`` or lower than ``<low mark>``, the
scheme is deactivated. If the value is lower than ``<mid mark>``, the scheme
is activated.
Statistics
~~~~~~~~~~
It also counts the total number and bytes of regions that each scheme is
applied. This statistics can be used for online analysis or tuning of the
schemes.
The statistics can be shown by reading the ``schemes`` file. Reading the file
will show each scheme you entered in each line, and the two numbers for the
statistics will be added at the end of each line.
Example
~~~~~~~
Below commands applies a scheme saying "If a memory region of size in [4KiB,
8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
interval in [10, 20], page out the region. For the paging out, use only up to
10ms per second, and also don't page out more than 1GiB per second. Under the
limitation, page out memory regions having longer age first. Also, check the
free memory rate of the system every 5 seconds, start the monitoring and paging
out when the free memory rate becomes lower than 50%, but stop it if the free
memory rate becomes larger than 60%, or lower than 30%".::
# cd <debugfs>/damon
# echo "4096 8192 0 5 10 20 2" > schemes
# cat schemes
4096 8192 0 5 10 20 2 0 0
# echo > schemes
The last two integers in the 4th line of above example is the total number and
the total size of the regions that the scheme is applied.
# scheme="4096 8192 0 5 10 20 2" # target access pattern and action
# scheme+=" 10 $((1024*1024*1024)) 1000" # quotas
# scheme+=" 0 0 100" # prioritization weights
# scheme+=" 1 5000000 600 500 300" # watermarks
# echo "$scheme" > schemes
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