The patch titled
Subject: Docs/mm/damon/design: clarify regions merging operation
has been added to the -mm mm-unstable branch. Its filename is
docs-mm-damon-design-clarify-regions-merging-operation.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/docs-mm-damon-design-clarify-regions-merging-operation.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: SeongJae Park <sj@xxxxxxxxxx>
Subject: Docs/mm/damon/design: clarify regions merging operation
Date: Mon, 1 Jul 2024 12:26:59 -0700
DAMON design document is not explaining how min_nr_regions limit is kept,
and what happens if the number of regions exceeds max_nr_regions. Add
more clarification for those.
Link: https://lkml.kernel.org/r/20240701192706.51415-3-sj@xxxxxxxxxx
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/mm/damon/design.rst | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
--- a/Documentation/mm/damon/design.rst~docs-mm-damon-design-clarify-regions-merging-operation
+++ a/Documentation/mm/damon/design.rst
@@ -209,11 +209,18 @@ the data access pattern can be dynamical
monitoring quality. To keep the assumption as much as possible, DAMON
adaptively merges and splits each region based on their access frequency.
-For each ``aggregation interval``, it compares the access frequencies of
-adjacent regions and merges those if the frequency difference is small. Then,
-after it reports and clears the aggregated access frequency of each region, it
-splits each region into two or three regions if the total number of regions
-will not exceed the user-specified maximum number of regions after the split.
+For each ``aggregation interval``, it compares the access frequencies
+(``nr_accesses``) of adjacent regions. If the difference is small, and if the
+sum of the two regions' sizes is smaller than the size of total regions divided
+by the ``minimum number of regions``, DAMON merges the two regions. If the
+resulting number of total regions is still higher than ``maximum number of
+regions``, it repeats the merging with increasing access frequenceis difference
+threshold until the upper-limit of the number of regions is met, or the
+threshold becomes higher than possible maximum value (``aggregation interval``
+divided by ``sampling interval``). Then, after it reports and clears the
+aggregated access frequency of each region, it splits each region into two or
+three regions if the total number of regions will not exceed the user-specified
+maximum number of regions after the split.
In this way, DAMON provides its best-effort quality and minimal overhead while
keeping the bounds users set for their trade-off.
_
Patches currently in -mm which might be from sj@xxxxxxxxxx are
mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet.patch
mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet-fix.patch
mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet-fix-2.patch
docs-mm-damon-design-fix-two-typos.patch
docs-mm-damon-design-clarify-regions-merging-operation.patch
docs-admin-guide-mm-damon-start-add-access-pattern-snapshot-example.patch
docs-mm-damon-design-add-links-from-overall-architecture-to-sections-of-details.patch
docs-mm-damon-design-move-configurable-operations-set-section-into-operations-set-layer-section.patch
docs-mm-damon-design-remove-programmable-modules-section-in-favor-of-modules-section.patch
docs-mm-damon-design-add-links-to-sections-of-damon-sysfs-interface-usage-doc.patch
docs-mm-damon-index-add-links-to-design.patch
docs-mm-damon-index-add-links-to-admin-guide-doc.patch
