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Docs/mm/damon/design: document data attributes monitoring

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Update DAMON design document for newly added data attributes monitoring
feature.

Link: https://lore.kernel.org/20260518234119.97569-21-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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SeongJae Park 2026-05-18 16:41:08 -07:00 committed by Andrew Morton
parent 14885da09b
commit f4e9895423
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37
Documentation/mm/damon/design.rst
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@ -276,6 +276,43 @@ interval``, DAMON checks if the region's size and access frequency
(``nr_accesses``) has significantly changed. If so, the counter is reset to
zero. Otherwise, the counter is increased.
Data Attributes Monitoring
~~~~~~~~~~~~~~~~~~~~~~~~~~
Data access pattern is only one type of data attributes. In some use cases,
users need to know more data attributes information. For example, users may
need to know how much of a given hot or cold memory region is backed by
anonymous pages, or belong to a specific cgroup. For such use case, data
attributes monitoring feature is provided.
Using the feature, users can register data attributes of their interest to the
DAMON :ref:`context <damon_design_execution_model_and_data_structures>`. The
registration is made by specifying a probe per attribute. Each of the probe
specifies a rule to determine if a given memory region has the related
attribute. The rule is constructed with multiple filters. The filters work
same to :ref:`DAMOS filters <damon_design_damos_filters>` except the supported
filter types. Currently only ``anon`` filter type is supported for data
attributes monitoring.
If such probes are registered, DAMON executes the probes for each region's
sampling memory when it does the access :ref:`sampling
<damon_design_region_based_sampling>`. The number of samples that identified
as having the data attribute (hitting the probe) per :ref:`aggregation interval
<damon_design_monitoring>` is accounted in a per-region per-probe counter.
Users can therefore know how much of a given DAMON region has a specific data
attribute by reading the per-region per-probe probe hits counter after each
aggregation interval.
This is a sampling based mechanism. Hence, it is lightweight but the output
may include some measurement errors. The output should be used with good
understanding of statistics.
Another way to do this for higher accuracy is using :ref:`DAMOS filter
<damon_design_damos_filters>` with ``stat`` :ref:`action
<damon_design_damos_action>` and ``sz_ops_filter_passed`` :ref:`stat
<damon_design_damos_stat>`. This approach provides the data attributes
information in page level. But, because it is operated in page level, the
overhead is proportional to the size of the memory.
Dynamic Target Space Updates Handling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~