mm/damon/schemes: activate schemes based on a watermarks mechanism

DAMON-based operation schemes need to be manually turned on and off.  In
some use cases, however, the condition for turning a scheme on and off
would depend on the system's situation.  For example, schemes for
proactive pages reclamation would need to be turned on when some memory
pressure is detected, and turned off when the system has enough free
memory.

For easier control of schemes activation based on the system situation,
this introduces a watermarks-based mechanism.  The client can describe
the watermark metric (e.g., amount of free memory in the system),
watermark check interval, and three watermarks, namely high, mid, and
low.  If the scheme is deactivated, it only gets the metric and compare
that to the three watermarks for every check interval.  If the metric is
higher than the high watermark, the scheme is deactivated.  If the
metric is between the mid watermark and the low watermark, the scheme is
activated.  If the metric is lower than the low watermark, the scheme is
deactivated again.  This is to allow users fall back to traditional
page-granularity mechanisms.

Link: https://lkml.kernel.org/r/20211019150731.16699-12-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Amit Shah <amit@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: David Woodhouse <dwmw@amazon.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Marco Elver <elver@google.com>
Cc: Markus Boehme <markubo@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 51 insertions, 1 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 1217566a0ebc..c93325efddd7 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -147,6 +147,45 @@ struct damos_quota {
 };
 
 /**
+ * enum damos_wmark_metric - Represents the watermark metric.
+ *
+ * @DAMOS_WMARK_NONE:		Ignore the watermarks of the given scheme.
+ * @DAMOS_WMARK_FREE_MEM_RATE:	Free memory rate of the system in [0,1000].
+ */
+enum damos_wmark_metric {
+	DAMOS_WMARK_NONE,
+	DAMOS_WMARK_FREE_MEM_RATE,
+};
+
+/**
+ * struct damos_watermarks - Controls when a given scheme should be activated.
+ * @metric:	Metric for the watermarks.
+ * @interval:	Watermarks check time interval in microseconds.
+ * @high:	High watermark.
+ * @mid:	Middle watermark.
+ * @low:	Low watermark.
+ *
+ * If &metric is &DAMOS_WMARK_NONE, the scheme is always active.  Being active
+ * means DAMON does monitoring and applying the action of the scheme to
+ * appropriate memory regions.  Else, DAMON checks &metric of the system for at
+ * least every &interval microseconds and works as below.
+ *
+ * If &metric is higher than &high, the scheme is inactivated.  If &metric is
+ * between &mid and &low, the scheme is activated.  If &metric is lower than
+ * &low, the scheme is inactivated.
+ */
+struct damos_watermarks {
+	enum damos_wmark_metric metric;
+	unsigned long interval;
+	unsigned long high;
+	unsigned long mid;
+	unsigned long low;
+
+/* private: */
+	bool activated;
+};
+
+/**
  * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
  * @min_sz_region:	Minimum size of target regions.
  * @max_sz_region:	Maximum size of target regions.
@@ -156,6 +195,7 @@ struct damos_quota {
  * @max_age_region:	Maximum age of target regions.
  * @action:		&damo_action to be applied to the target regions.
  * @quota:		Control the aggressiveness of this scheme.
+ * @wmarks:		Watermarks for automated (in)activation of this scheme.
  * @stat_count:		Total number of regions that this scheme is applied.
  * @stat_sz:		Total size of regions that this scheme is applied.
  * @list:		List head for siblings.
@@ -166,6 +206,14 @@ struct damos_quota {
  * those.  To avoid consuming too much CPU time or IO resources for the
  * &action, &quota is used.
  *
+ * To do the work only when needed, schemes can be activated for specific
+ * system situations using &wmarks.  If all schemes that registered to the
+ * monitoring context are inactive, DAMON stops monitoring either, and just
+ * repeatedly checks the watermarks.
+ *
+ * If all schemes that registered to a &struct damon_ctx are inactive, DAMON
+ * stops monitoring and just repeatedly checks the watermarks.
+ *
  * After applying the &action to each region, &stat_count and &stat_sz is
  * updated to reflect the number of regions and total size of regions that the
  * &action is applied.
@@ -179,6 +227,7 @@ struct damos {
 	unsigned int max_age_region;
 	enum damos_action action;
 	struct damos_quota quota;
+	struct damos_watermarks wmarks;
 	unsigned long stat_count;
 	unsigned long stat_sz;
 	struct list_head list;
@@ -384,7 +433,8 @@ struct damos *damon_new_scheme(
 		unsigned long min_sz_region, unsigned long max_sz_region,
 		unsigned int min_nr_accesses, unsigned int max_nr_accesses,
 		unsigned int min_age_region, unsigned int max_age_region,
-		enum damos_action action, struct damos_quota *quota);
+		enum damos_action action, struct damos_quota *quota,
+		struct damos_watermarks *wmarks);
 void damon_add_scheme(struct damon_ctx *ctx, struct damos *s);
 void damon_destroy_scheme(struct damos *s);