mm/damon/core: add more comments for nr_accesses

The comment on struct damon_region about nr_accesses field looks not
sufficient.  Many people actually used to ask what nr_accesses mean.
There is more detailed explanation of the mechanism on the comment for
struct damon_attrs, but it is also ambiguous, as it doesn't specify the
name of the counter for aggregating the access check results.  Make
those more detailed.

Link: https://lkml.kernel.org/r/20230907022929.91361-10-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/damon.h

@@ -43,6 +43,10 @@ struct damon_addr_range {
  * @list:		List head for siblings.
  * @age:		Age of this region.
  *
+ * @nr_accesses is reset to zero for every &damon_attrs->aggr_interval and be
+ * increased for every &damon_attrs->sample_interval if an access to the region
+ * during the last sampling interval is found.
+ *
  * @age is initially zero, increased for each aggregation interval, and reset
  * to zero again if the access frequency is significantly changed.  If two
  * regions are merged into a new region, both @nr_accesses and @age of the new
@@ -472,13 +476,14 @@ struct damon_callback {
  *				regions.
  *
  * For each @sample_interval, DAMON checks whether each region is accessed or
- * not.  It aggregates and keeps the access information (number of accesses to
- * each region) for @aggr_interval time.  DAMON also checks whether the target
- * memory regions need update (e.g., by ``mmap()`` calls from the application,
- * in case of virtual memory monitoring) and applies the changes for each
- * @ops_update_interval.  All time intervals are in micro-seconds.
- * Please refer to &struct damon_operations and &struct damon_callback for more
- * detail.
+ * not during the last @sample_interval.  If such access is found, DAMON
+ * aggregates the information by increasing &damon_region->nr_accesses for
+ * @aggr_interval time.  For each @aggr_interval, the count is reset.  DAMON
+ * also checks whether the target memory regions need update (e.g., by
+ * ``mmap()`` calls from the application, in case of virtual memory monitoring)
+ * and applies the changes for each @ops_update_interval.  All time intervals
+ * are in micro-seconds.  Please refer to &struct damon_operations and &struct
+ * damon_callback for more detail.
  */
 struct damon_attrs {
 	unsigned long sample_interval;