[RFC PATCH v1.3 04/18] mm/damon/core: handle unreset nr_accesses in damon_nr_accesses_mvsum()

[SeongJae Park <sj@kernel.org>]

damon_set_attrs() works like reverting aggregations that were made so
far for this aggregation window.  If this is the end of the aggregation,
however, kdamond_fn() will do the operations at the end of the
aggregation interval, using cached timestamps.  For such operations that
rely on damon_region->nr_accesses, damon_update_monitoring_results()
doesn't reset the nr_accesses if it is called at the end of the
aggregation window.

damon_nr_accesses_mvsum() works with fresh timestamps, though.  The
nr_accesses that are not reset in this case can make the logic to
unnecessarily count nr_accesses, resulting in returning
higher-than-expected pseudo moving sum nr_accesses.  No code is using
damon_nr_accesses_mvsum() yet, so this is not causing a real problem.
Following commits will add usage of the function, though.  For safe
usages, calculate the pseudo moving sum without nr_accesses if the
remaining window is full.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 191533685cf2f..9d501ad34f44c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -268,6 +268,9 @@ unsigned int damon_nr_accesses_mvsum(struct damon_region *r,
 			ctx->passed_sample_intervals;
 	left_window_bp = mult_frac(left_window, 10000, window_len);
 
+	if (left_window_bp == 10000)
+		return r->last_nr_accesses;
+
 	return damon_mvsum(r->nr_accesses, r->last_nr_accesses,
 			left_window_bp);
 }
-- 
2.47.3