mm/damon/core: implement scheme-specific apply interval

DAMON-based operation schemes are applied for every aggregation interval. 
That was mainly because schemes were using nr_accesses, which be complete
to be used for every aggregation interval.  However, the schemes are now
using nr_accesses_bp, which is updated for each sampling interval in a way
that reasonable to be used.  Therefore, there is no reason to apply
schemes for each aggregation interval.

The unnecessary alignment with aggregation interval was also making some
use cases of DAMOS tricky.  Quotas setting under long aggregation interval
is one such example.  Suppose the aggregation interval is ten seconds, and
there is a scheme having CPU quota 100ms per 1s.  The scheme will actually
uses 100ms per ten seconds, since it cannobe be applied before next
aggregation interval.  The feature is working as intended, but the results
might not that intuitive for some users.  This could be fixed by updating
the quota to 1s per 10s.  But, in the case, the CPU usage of DAMOS could
look like spikes, and would actually make a bad effect to other
CPU-sensitive workloads.

Implement a dedicated timing interval for each DAMON-based operation
scheme, namely apply_interval.  The interval will be sampling interval
aligned, and each scheme will be applied for its apply_interval.  The
interval is set to 0 by default, and it means the scheme should use the
aggregation interval instead.  This avoids old users getting any
behavioral difference.

Link: https://lkml.kernel.org/r/20230916020945.47296-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

5 files changed, 72 insertions, 9 deletions

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 79fef5145a4b..5eb649bd002f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -313,7 +313,9 @@ static struct damos_quota *damos_quota_init_priv(struct damos_quota *quota)
 }
 
 struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
-			enum damos_action action, struct damos_quota *quota,
+			enum damos_action action,
+			unsigned long apply_interval_us,
+			struct damos_quota *quota,
 			struct damos_watermarks *wmarks)
 {
 	struct damos *scheme;
@@ -323,6 +325,13 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 		return NULL;
 	scheme->pattern = *pattern;
 	scheme->action = action;
+	scheme->apply_interval_us = apply_interval_us;
+	/*
+	 * next_apply_sis will be set when kdamond starts.  While kdamond is
+	 * running, it will also updated when it is added to the DAMON context,
+	 * or damon_attrs are updated.
+	 */
+	scheme->next_apply_sis = 0;
 	INIT_LIST_HEAD(&scheme->filters);
 	scheme->stat = (struct damos_stat){};
 	INIT_LIST_HEAD(&scheme->list);
@@ -335,9 +344,21 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	return scheme;
 }
 
+static void damos_set_next_apply_sis(struct damos *s, struct damon_ctx *ctx)
+{
+	unsigned long sample_interval = ctx->attrs.sample_interval ?
+		ctx->attrs.sample_interval : 1;
+	unsigned long apply_interval = s->apply_interval_us ?
+		s->apply_interval_us : ctx->attrs.aggr_interval;
+
+	s->next_apply_sis = ctx->passed_sample_intervals +
+		apply_interval / sample_interval;
+}
+
 void damon_add_scheme(struct damon_ctx *ctx, struct damos *s)
 {
 	list_add_tail(&s->list, &ctx->schemes);
+	damos_set_next_apply_sis(s, ctx);
 }
 
 static void damon_del_scheme(struct damos *s)
@@ -558,6 +579,7 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
 {
 	unsigned long sample_interval = attrs->sample_interval ?
 		attrs->sample_interval : 1;
+	struct damos *s;
 
 	if (attrs->min_nr_regions < 3)
 		return -EINVAL;
@@ -573,6 +595,10 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
 
 	damon_update_monitoring_results(ctx, attrs);
 	ctx->attrs = *attrs;
+
+	damon_for_each_scheme(s, ctx)
+		damos_set_next_apply_sis(s, ctx);
+
 	return 0;
 }
 
@@ -1094,14 +1120,29 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 	struct damon_target *t;
 	struct damon_region *r, *next_r;
 	struct damos *s;
+	unsigned long sample_interval = c->attrs.sample_interval ?
+		c->attrs.sample_interval : 1;
+	bool has_schemes_to_apply = false;
 
 	damon_for_each_scheme(s, c) {
+		if (c->passed_sample_intervals != s->next_apply_sis)
+			continue;
+
+		s->next_apply_sis +=
+			(s->apply_interval_us ? s->apply_interval_us :
+			 c->attrs.aggr_interval) / sample_interval;
+
 		if (!s->wmarks.activated)
 			continue;
 
+		has_schemes_to_apply = true;
+
 		damos_adjust_quota(c, s);
 	}
 
+	if (!has_schemes_to_apply)
+		return;
+
 	damon_for_each_target(t, c) {
 		damon_for_each_region_safe(r, next_r, t)
 			damon_do_apply_schemes(c, t, r);
@@ -1372,11 +1413,19 @@ static void kdamond_init_intervals_sis(struct damon_ctx *ctx)
 {
 	unsigned long sample_interval = ctx->attrs.sample_interval ?
 		ctx->attrs.sample_interval : 1;
+	unsigned long apply_interval;
+	struct damos *scheme;
 
 	ctx->passed_sample_intervals = 0;
 	ctx->next_aggregation_sis = ctx->attrs.aggr_interval / sample_interval;
 	ctx->next_ops_update_sis = ctx->attrs.ops_update_interval /
 		sample_interval;
+
+	damon_for_each_scheme(scheme, ctx) {
+		apply_interval = scheme->apply_interval_us ?
+			scheme->apply_interval_us : ctx->attrs.aggr_interval;
+		scheme->next_apply_sis = apply_interval / sample_interval;
+	}
 }
 
 /*
@@ -1428,19 +1477,28 @@ static int kdamond_fn(void *data)
 		if (ctx->ops.check_accesses)
 			max_nr_accesses = ctx->ops.check_accesses(ctx);
 
-		sample_interval = ctx->attrs.sample_interval ?
-			ctx->attrs.sample_interval : 1;
 		if (ctx->passed_sample_intervals == next_aggregation_sis) {
-			ctx->next_aggregation_sis = next_aggregation_sis +
-				ctx->attrs.aggr_interval / sample_interval;
 			kdamond_merge_regions(ctx,
 					max_nr_accesses / 10,
 					sz_limit);
 			if (ctx->callback.after_aggregation &&
 					ctx->callback.after_aggregation(ctx))
 				break;
-			if (!list_empty(&ctx->schemes))
-				kdamond_apply_schemes(ctx);
+		}
+
+		/*
+		 * do kdamond_apply_schemes() after kdamond_merge_regions() if
+		 * possible, to reduce overhead
+		 */
+		if (!list_empty(&ctx->schemes))
+			kdamond_apply_schemes(ctx);
+
+		sample_interval = ctx->attrs.sample_interval ?
+			ctx->attrs.sample_interval : 1;
+		if (ctx->passed_sample_intervals == next_aggregation_sis) {
+			ctx->next_aggregation_sis = next_aggregation_sis +
+				ctx->attrs.aggr_interval / sample_interval;
+
 			kdamond_reset_aggregated(ctx);
 			kdamond_split_regions(ctx);
 			if (ctx->ops.reset_aggregated)
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 124f0f8c97b7..dc0ea1fc30ca 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -278,7 +278,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 			goto fail;
 
 		pos += parsed;
-		scheme = damon_new_scheme(&pattern, action, &quota, &wmarks);
+		scheme = damon_new_scheme(&pattern, action, 0, &quota,
+				&wmarks);
 		if (!scheme)
 			goto fail;
 
diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 7b8fce2f67a8..3ecdcc029443 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -158,6 +158,8 @@ static struct damos *damon_lru_sort_new_scheme(
 			pattern,
 			/* (de)prioritize on LRU-lists */
 			action,
+			/* for each aggregation interval */
+			0,
 			/* under the quota. */
 			&quota,
 			/* (De)activate this according to the watermarks. */
diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 648d2a85523a..ab974e477d2f 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -142,6 +142,8 @@ static struct damos *damon_reclaim_new_scheme(void)
 			&pattern,
 			/* page out those, as soon as found */
 			DAMOS_PAGEOUT,
+			/* for each aggregation interval */
+			0,
 			/* under the quota. */
 			&damon_reclaim_quota,
 			/* (De)activate this according to the watermarks. */
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 093700f50b18..3d30e85596b0 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1610,7 +1610,7 @@ static struct damos *damon_sysfs_mk_scheme(
 		.low = sysfs_wmarks->low,
 	};
 
-	scheme = damon_new_scheme(&pattern, sysfs_scheme->action, &quota,
+	scheme = damon_new_scheme(&pattern, sysfs_scheme->action, 0, &quota,
 			&wmarks);
 	if (!scheme)
 		return NULL;