+ mm-damon-core-always-update-last_nr_accesses-for-intervals-change.patch added to mm-new branch

+ mm-damon-core-always-update-last_nr_accesses-for-intervals-change.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/core: always update ->last_nr_accesses for intervals change
has been added to the -mm mm-new branch.  Its filename is
     mm-damon-core-always-update-last_nr_accesses-for-intervals-change.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-always-update-last_nr_accesses-for-intervals-change.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: SJ Park <sj@kernel.org>
Subject: mm/damon/core: always update ->last_nr_accesses for intervals change
Date: Mon, 29 Jun 2026 21:07:56 -0700

Each iteration of kdamond_fn() main loop caches and use the next
aggregation time (next_aggregation_sis) because it can be updated in the
middle, inside kdamond_call().  If that happens,
damon_update_monitoring_result() is called for scaling the access
frequency information of each region according to the changed intervals. 
The function does not update damon_region->last_nr_accesses when it is at
the end of the aggregation, because it will anyway be reset after the
function is executed, in kdamond_reset_aggregated().

Let's suppose damon_nr_accesses_mvsum() is called with the not yet updated
last_nr_accesses.  It will use the fresh next_aggregation_sis in the
context instead of the cached one, unlike kdamond_fn().  As a result, use
of not updated last_nr_acceses with the updated next_aggregation_sis
result in returning wrong value.

There is no such damon_nr_accesses_nvsum() call at the moment, so this is
no problem.  It is planned to add such calls, though.  Prevent the issue
by updating last_nr_accesses always.  This adds overhead, but that's fine
because the overhead is not big, and it is anyway not a fast path.

Link: https://lore.kernel.org/20260630040812.149729-4-sj@kernel.org
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/core.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/damon/core.c~mm-damon-core-always-update-last_nr_accesses-for-intervals-change
+++ a/mm/damon/core.c
@@ -871,6 +871,8 @@ static void damon_update_monitoring_resu
 		struct damon_attrs *old_attrs, struct damon_attrs *new_attrs,
 		bool aggregating)
 {
+	r->last_nr_accesses = damon_nr_accesses_for_new_attrs(
+			r->last_nr_accesses, old_attrs, new_attrs);
 	if (!aggregating) {
 		r->nr_accesses = damon_nr_accesses_for_new_attrs(
 				r->nr_accesses, old_attrs, new_attrs);
@@ -882,8 +884,6 @@ static void damon_update_monitoring_resu
 		 * interval.  In other words, make the status like
 		 * kdamond_reset_aggregated() is called.
 		 */
-		r->last_nr_accesses = damon_nr_accesses_for_new_attrs(
-				r->last_nr_accesses, old_attrs, new_attrs);
 		r->nr_accesses_bp = r->last_nr_accesses * 10000;
 		r->nr_accesses = 0;
 	}
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-sysfs-schemes-fix-dir-put-orders-in-access_pattern_add_dirs.patch
mm-damon-sysfs-schemes-put-stats-for-scheme_add_dirs-internal-error.patch
mm-damon-ops-common-handle-extreme-intervals-in-damon_hot_score.patch
mm-damon-add-a-kernel-doc-comment-for-damon_ctx-probes.patch
mm-damon-add-a-kernel-doc-comment-for-damon_ctx-rnd_state.patch
maintainers-s-seongjae-sj.patch
samples-damon-wsse-handle-damon_start-failure.patch
samples-damon-prcl-handle-damon_start-failure.patch
samples-damon-mtier-handle-damon_start-failure.patch
samples-damon-mtier-handle-damon_stop-failure.patch
samples-damon-wsse-stop-and-free-damon-ctx-when-damon_call-fails.patch
samples-damon-prcl-stop-and-free-damon-ctx-when-damon_call-fails.patch
mm-damon-sysfs-kobject_del-target-normal-context-and-kdamond-dirs.patch
mm-damon-sysfs-kobject_del-region-and-target-error-dirs.patch
mm-damon-sysfs-schemes-kobject_del-scheme-dirs.patch
mm-damon-sysfs-schemes-kobject_del-scheme-region-dirs.patch
mm-damon-sysfs-schemes-kobject_del-scheme-filter-dirs.patch
mm-damon-sysfs-schemes-kobject_del-scheme-quota-goal-dirs.patch
mm-damon-sysfs-schemes-kobject_del-scheme-action-destination-dirs.patch
mm-damon-sysfs-kobject_del-probe-dirs.patch
mm-damon-sysfs-kobject_del-probe-filter-dirs.patch
mm-damon-sysfs-kobject_del-probe-dirs-in-probes_addd_dir-error-path.patch
mm-damon-sysfs-schemes-kobject_del-region-for-populate_region-error.patch
docs-mm-damon-design-update-for-damos_quota_node_eligible_mem_bp.patch
docs-abi-damon-document-probe-files.patch
mm-damon-tests-core-kunit-test-damon_rand.patch
selftests-damon-sysfssh-test-multiple-probe-dirs-creation.patch
selftests-damon-sysfssh-test-coreops_filters-directories.patch
selftests-damon-sysfssh-test-dests-dir.patch
selftests-damon-sysfssh-test-all-files-in-quota-goal-dir.patch
mm-damon-core-reduce-range-setup-in-damon_commit_target_regions.patch
mm-damon-sysfs-split-probe-setup-function-out.patch
mm-damon-sysfs-split-out-filters-setup-function.patch
mm-damon-sysfs-fix-typos-in-probe_addrm_dirs-s-attr-probe.patch
mm-damon-core-introduce-damon_nr_accesses_mvsum.patch
mm-damon-tests-core-kunit-test-damon_mvsum.patch
mm-damon-core-always-update-last_nr_accesses-for-intervals-change.patch
mm-damon-core-handle-unreset-nr_accesses-in-damon_nr_accesses_mvsum.patch
mm-damon-core-use-damon_nr_accesses_mvsum-in-__damos_valid_target.patch
mm-damon-core-use-damon_nr_accesses_mvsum-for-damos-region-tracing.patch
mm-damon-sysfs-schemes-use-damon_nr_accesses_mvsum-for-damo-regions.patch
mm-damon-core-remove-damon_warn_fix_nr_accesses_corruption.patch
mm-damon-core-remove-damon_verify_reset_aggregated.patch
mm-damon-core-remove-damon_verify_merge_regions_of.patch
mm-damon-tests-core-kunit-remove-nr_accesses_bp-setup-and-tests.patch
selftests-damon-drgn_dump_damon_status-do-not-dump-nr_accesses_bp.patch
mm-damon-core-remove-nr_accesses_bp-setups-and-updates.patch
mm-damon-core-remove-attrs-param-from-damon_update_region_access_rate.patch
mm-damon-paddr-remove-attrs-param-from-__damon_pa_check_access.patch
mm-damon-vaddr-remove-attrs-param-from-__damon_va_check_access.patch
mm-damon-core-remove-damon_moving_sum-and-its-unit-test.patch
mm-damon-core-remove-damon_region-nr_accesses_bp.patch