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Message-Id: <20250228220328.49438-3-sj@kernel.org>
Date: Fri, 28 Feb 2025 14:03:22 -0800
From: SeongJae Park <sj@...nel.org>
To:
Cc: SeongJae Park <sj@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
damon@...ts.linux.dev,
kernel-team@...a.com,
linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: [RFC PATCH v2 2/8] mm/damon/core: implement intervals auto-tuning
Implement the DAMON sampling and aggregation intervals auto-tuning
mechanism as briefly described on 'struct damon_intervals_goal'. The
core part for deciding the direction and amount of the changes is
implemented reusing the feedback loop function which is being used for
DAMOS quotas auto-tuning. Unlike the DAMOS quotas auto-tuning use case,
limit the maximum decreasing amount after the adjustment to 50% of the
current value, though. This is because the intervals have no good
merits at rapid reductions since it could unnecessarily increase the
monitoring overhead.
Signed-off-by: SeongJae Park <sj@...nel.org>
---
include/linux/damon.h | 16 +++++++++
mm/damon/core.c | 76 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 92 insertions(+)
diff --git a/include/linux/damon.h b/include/linux/damon.h
index 130c3e01089c..eed008b64a23 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -718,6 +718,17 @@ struct damon_attrs {
struct damon_intervals_goal intervals_goal;
unsigned long min_nr_regions;
unsigned long max_nr_regions;
+/* private: internal use only */
+ /*
+ * @aggr_interval to @sample_interval ratio.
+ * Core-external components call damon_set_attrs() with &damon_attrs
+ * that this field is unset. In the case, damon_set_attrs() sets this
+ * field of resulting &damon_attrs. Core-internal components such as
+ * kdamond_tune_intervals() calls damon_set_attrs() with &damon_attrs
+ * that this field is set. In the case, damon_set_attrs() just keep
+ * it.
+ */
+ unsigned long aggr_samples;
};
/**
@@ -766,6 +777,11 @@ struct damon_ctx {
* update
*/
unsigned long next_ops_update_sis;
+ /*
+ * number of sample intervals that should be passed before next
+ * intervals tuning
+ */
+ unsigned long next_intervals_tune_sis;
/* for waiting until the execution of the kdamond_fn is started */
struct completion kdamond_started;
/* for scheme quotas prioritization */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index b11595c01c37..d4fc2c907cfc 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -687,6 +687,10 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
if (attrs->sample_interval > attrs->aggr_interval)
return -EINVAL;
+ /* calls from core-external doesn't set this. */
+ if (!attrs->aggr_samples)
+ attrs->aggr_samples = attrs->aggr_interval / sample_interval;
+
ctx->next_aggregation_sis = ctx->passed_sample_intervals +
attrs->aggr_interval / sample_interval;
ctx->next_ops_update_sis = ctx->passed_sample_intervals +
@@ -1392,6 +1396,65 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
}
}
+static unsigned long damon_get_intervals_score(struct damon_ctx *c)
+{
+ struct damon_target *t;
+ struct damon_region *r;
+ unsigned long sz_region, max_access_events = 0, access_events = 0;
+ unsigned long target_access_events;
+ unsigned long goal_bp = c->attrs.intervals_goal.access_bp;
+
+ damon_for_each_target(t, c) {
+ damon_for_each_region(r, t) {
+ sz_region = damon_sz_region(r);
+ max_access_events += sz_region * c->attrs.aggr_samples;
+ access_events += sz_region * r->nr_accesses;
+ }
+ }
+ target_access_events = max_access_events * goal_bp / 10000;
+ return access_events * 10000 / target_access_events;
+}
+
+static unsigned long damon_feed_loop_next_input(unsigned long last_input,
+ unsigned long score);
+
+static unsigned long damon_get_intervals_adaptation_bp(struct damon_ctx *c)
+{
+ unsigned long score_bp, adaptation_bp;
+
+ score_bp = damon_get_intervals_score(c);
+ adaptation_bp = damon_feed_loop_next_input(100000000, score_bp) /
+ 10000;
+ /*
+ * adaptaion_bp ranges from 1 to 20,000. Avoid too rapid reduction of
+ * the intervals by rescaling [1,10,000] to [5000, 10,000].
+ */
+ if (adaptation_bp <= 10000)
+ adaptation_bp = 5000 + adaptation_bp / 2;
+ return adaptation_bp;
+}
+
+static void kdamond_tune_intervals(struct damon_ctx *c)
+{
+ unsigned long adaptation_bp;
+ struct damon_attrs new_attrs;
+ struct damon_intervals_goal *goal;
+
+ adaptation_bp = damon_get_intervals_adaptation_bp(c);
+ if (adaptation_bp == 10000)
+ return;
+
+ new_attrs = c->attrs;
+ goal = &c->attrs.intervals_goal;
+ new_attrs.sample_interval = min(goal->max_sample_us,
+ c->attrs.sample_interval * adaptation_bp / 10000);
+ new_attrs.sample_interval = max(goal->min_sample_us,
+ new_attrs.sample_interval);
+ new_attrs.aggr_interval = new_attrs.sample_interval *
+ c->attrs.aggr_samples;
+ damon_set_attrs(c, &new_attrs);
+}
+
static void damon_split_region_at(struct damon_target *t,
struct damon_region *r, unsigned long sz_r);
@@ -2300,6 +2363,8 @@ static void kdamond_init_intervals_sis(struct damon_ctx *ctx)
ctx->next_aggregation_sis = ctx->attrs.aggr_interval / sample_interval;
ctx->next_ops_update_sis = ctx->attrs.ops_update_interval /
sample_interval;
+ ctx->next_intervals_tune_sis = ctx->next_aggregation_sis *
+ ctx->attrs.intervals_goal.aggrs;
damon_for_each_scheme(scheme, ctx) {
apply_interval = scheme->apply_interval_us ?
@@ -2384,6 +2449,17 @@ static int kdamond_fn(void *data)
sample_interval = ctx->attrs.sample_interval ?
ctx->attrs.sample_interval : 1;
if (ctx->passed_sample_intervals >= next_aggregation_sis) {
+ if (ctx->attrs.intervals_goal.aggrs &&
+ ctx->passed_sample_intervals >=
+ ctx->next_intervals_tune_sis) {
+ ctx->next_intervals_tune_sis +=
+ ctx->attrs.aggr_samples *
+ ctx->attrs.intervals_goal.aggrs;
+ kdamond_tune_intervals(ctx);
+ sample_interval = ctx->attrs.sample_interval ?
+ ctx->attrs.sample_interval : 1;
+
+ }
ctx->next_aggregation_sis = next_aggregation_sis +
ctx->attrs.aggr_interval / sample_interval;
--
2.39.5
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