Docs/mm/damon/design: document 'address unit' parameter

Add 'addr_unit' parameter description on DAMON design document.

Link: https://lkml.kernel.org/r/20250828171242.59810-9-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: ze zuo <zuoze1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index 2f6ba5c7f4c7642bc3e88ed18a5ba3ef29188885..d9d5baa1ec873ba0e3697dd72493e8b9ba03c729 100644 (file)
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -67,7 +67,7 @@ processes, NUMA nodes, files, and backing memory devices would be supportable.
 Also, if some architectures or devices support special optimized access check
 features, those will be easily configurable.
 
-DAMON currently provides below three operation sets.  Below two subsections
+DAMON currently provides below three operation sets.  Below three subsections
 describe how those work.
 
  - vaddr: Monitor virtual address spaces of specific processes
@@ -135,6 +135,18 @@ the interference is the responsibility of sysadmins.  However, it solves the
 conflict with the reclaim logic using ``PG_idle`` and ``PG_young`` page flags,
 as Idle page tracking does.
 
+Address Unit
+------------
+
+DAMON core layer uses ``unsinged long`` type for monitoring target address
+ranges.  In some cases, the address space for a given operations set could be
+too large to be handled with the type.  ARM (32-bit) with large physical
+address extension is an example.  For such cases, a per-operations set
+parameter called ``address unit`` is provided.  It represents the scale factor
+that need to be multiplied to the core layer's address for calculating real
+address on the given address space.  Support of ``address unit`` parameter is
+up to each operations set implementation.  ``paddr`` is the only operations set
+implementation that supports the parameter.
 
 .. _damon_core_logic: