mm/damon/schemes: account how many times quota limit has exceeded

If the time/space quotas of a given DAMON-based operation scheme is too
small, the scheme could show unexpectedly slow progress.  However, there
is no good way to notice the case in runtime.  This commit extends the
DAMOS stat to provide how many times the quota limits exceeded so that
the users can easily notice the case and tune the scheme.

Link: https://lkml.kernel.org/r/20211210150016.35349-3-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/damon.h

@@ -198,12 +198,14 @@ struct damos_watermarks {
  * @sz_tried:	Total size of regions that the scheme is tried to be applied.
  * @nr_applied:	Total number of regions that the scheme is applied.
  * @sz_applied:	Total size of regions that the scheme is applied.
+ * @qt_exceeds: Total number of times the quota of the scheme has exceeded.
  */
 struct damos_stat {
 	unsigned long nr_tried;
 	unsigned long sz_tried;
 	unsigned long nr_applied;
 	unsigned long sz_applied;
+	unsigned long qt_exceeds;
 };
 
 /**

mm/damon/core.c

@@ -693,6 +693,8 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 		if (time_after_eq(jiffies, quota->charged_from +
 					msecs_to_jiffies(
 						quota->reset_interval))) {
+			if (quota->esz && quota->charged_sz >= quota->esz)
+				s->stat.qt_exceeds++;
 			quota->total_charged_sz += quota->charged_sz;
 			quota->charged_from = jiffies;
 			quota->charged_sz = 0;