linux-kernel - [RFC PATCH v3 24/37] Docs/mm/damon/design: document sample filters

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Message-ID: <20251208062943.68824-25-sj@kernel.org>
Date: Sun,  7 Dec 2025 22:29:28 -0800
From: SeongJae Park <sj@...nel.org>
To: 
Cc: SeongJae Park <sj@...nel.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	damon@...ts.linux.dev,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH v3 24/37] Docs/mm/damon/design: document sample filters

Update DAMON design document for the access sample results filtering.

Signed-off-by: SeongJae Park <sj@...nel.org>
---
 Documentation/mm/damon/design.rst | 42 +++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index a21973b33bc3..9a4679de437f 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -146,12 +146,17 @@ do the access check using monitoring-purpose page fault events in a way similar
 to NUMA balancing hinting faults.  When it is being used, ``paddr`` installs
 the page protection in a way similar to that of NUMA balancing hinting faults.
 Then the page fault handler reports the faults happend by the installed page
-protection to DAMON core layer.
+protection to DAMON core layer.  Compared to the accessed-bit based one, this
+approach gives more information to DAMON, such as the access-generated
+CPU.
 
 ``paddr`` uses :ref:`accessed-bit based check
 <damon_design_pte_accessed_bit_access_check>` by default, and users can change
 it to use this page faults based one, using :ref:`access sampling primitives
-selection <damon_design_sampling_primitives_selection>`.
+selection <damon_design_sampling_primitives_selection>`.  Also, the addtional
+information can be used for doing monitoring of only specific type accesses,
+using :ref:`access sampling results filters
+<damon_design_sampling_results_filters>`.
 
 .. _damon_design_addr_unit:
 
@@ -277,6 +282,39 @@ support from the operations set implementation for virtual address spaces
 
 At the moment, only exclusive use of the primitives is supported.
 
+.. _damon_design_sampling_results_filters:
+
+Access Sampling Results Filter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Depending on the access sampling primitives that used, the sampling results
+could inform more than whether an access is made, such as the CPU or the thread
+the sampled access was made from, and whether the sampled access was for
+writing or reading.  By filtering the results based on the additional
+information, DAMON can perform for more detailed access monitoring, such as
+per-CPUs/threads or read/write-only monitoring.
+
+For such special types of monitoring, DAMON provides a feature called "sampling
+results filter".  The feature allows users to set an arbitrary number of
+filters for the sampling results.  Each of the filters specifies
+
+- a type of the additional information (``type``),
+- whether it is for the sampling results of the type or all except the type
+  (``matching``), and
+- whether it is to allow (include) or reject (exclude) consuming of the type of
+  sampling results.
+
+Each filter is applied in the order of the installation.  Only sampling results
+that allowed by previous filters are continue to be evaluated by the next
+filters.  If a sampling result is decided to be rejected by a filter, it is
+just discarded and no later filter is applied.
+
+Below ``type`` of access sampling results filter are currently supported.
+
+- cpumask
+    - Whether the sampled access was generated by a cpu that included in a
+      given cpumask.
+
 
 .. _damon_design_age_tracking:
 
-- 
2.47.3