[PATCH v22 04/18] mm/damon: Track dynamic monitoring target regions update

[SeongJae Park]

From: SeongJae Park <sjpark@xxxxxxxxx>

The monitoring target address range can be dynamically changed.  For
example, virtual memory could be dynamically mapped and unmapped.
Physical memory could be hot-plugged.

As the changes could be quite frequent in some cases, DAMON checks the
dynamic memory mapping changes and applies it to the abstracted target
area only for each of a user-specified time interval, ``regions update
interval``.

Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx>
---
 include/linux/damon.h | 22 +++++++++++++++++-----
 mm/damon/core.c       | 22 ++++++++++++++++++++--
 2 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 0797bdfbfc24..b8562814751e 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -60,6 +60,7 @@ struct damon_ctx;
  * struct damon_primitive	Monitoring primitives for given use cases.
  *
  * @init_target_regions:	Constructs initial monitoring target regions.
+ * @update_target_regions:	Updates monitoring target regions.
  * @prepare_access_checks:	Prepares next access check of target regions.
  * @check_accesses:		Checks the access of target regions.
  * @target_valid:		Determine if the target is valid.
@@ -68,12 +69,17 @@ struct damon_ctx;
  * DAMON can be extended for various address spaces and usages.  For this,
  * users should register the low level primitives for their target address
  * space and usecase via the &damon_ctx.primitive.  Then, the monitoring thread
- * calls @init_target_regions before starting the monitoring and
+ * calls @init_target_regions before starting the monitoring,
+ * @update_target_regions for each @regions_update_interval, and
  * @prepare_access_checks, @check_accesses, and @target_valid for each
  * @sample_interval.
+
  *
  * @init_target_regions should construct proper monitoring target regions and
  * link those to the DAMON context struct.
+ * @update_target_regions should update the monitoring target regions for
+ * current status.
+
  * @prepare_access_checks should manipulate the monitoring regions to be
  * prepare for the next access check.
  * @check_accesses should check the accesses to each region that made after the
@@ -87,6 +93,7 @@ struct damon_ctx;
  */
 struct damon_primitive {
 	void (*init_target_regions)(struct damon_ctx *context);
+	void (*update_target_regions)(struct damon_ctx *context);
 	void (*prepare_access_checks)(struct damon_ctx *context);
 	unsigned int (*check_accesses)(struct damon_ctx *context);
 	bool (*target_valid)(struct damon_target *target);
@@ -132,13 +139,16 @@ struct damon_callback {
  *
  * @sample_interval:		The time between access samplings.
  * @aggr_interval:		The time between monitor results aggregations.
+ * @regions_update_interval:	The time between monitor regions updates.
  * @min_nr_regions:		The minimum number of monitoring regions.
  * @max_nr_regions:		The maximum number of monitoring 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.  All time intervals are in
- * micro-seconds.
+ * 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
+ * @regions_update_interval.  All time intervals are in micro-seconds.
  *
  * @kdamond:		Kernel thread who does the monitoring.
  * @kdamond_stop:	Notifies whether kdamond should stop.
@@ -167,10 +177,12 @@ struct damon_callback {
 struct damon_ctx {
 	unsigned long sample_interval;
 	unsigned long aggr_interval;
+	unsigned long regions_update_interval;
 	unsigned long min_nr_regions;
 	unsigned long max_nr_regions;
 
 	struct timespec64 last_aggregation;
+	struct timespec64 last_regions_update;
 
 	struct task_struct *kdamond;
 	bool kdamond_stop;
@@ -216,8 +228,8 @@ unsigned int damon_nr_regions(struct damon_target *t);
 
 int damon_set_targets(struct damon_ctx *ctx,
 		unsigned long *ids, ssize_t nr_ids);
-int damon_set_attrs(struct damon_ctx *ctx,
-		unsigned long sample_int, unsigned long aggr_int,
+int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
+		unsigned long aggr_int, unsigned long regions_update_int,
 		unsigned long min_nr_reg, unsigned long max_nr_reg);
 
 int damon_nr_running_ctxs(void);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index ed364b42721d..36428327e848 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -167,6 +167,7 @@ int damon_set_targets(struct damon_ctx *ctx,
  * damon_set_attrs() - Set attributes for the monitoring.
  * @ctx:		monitoring context
  * @sample_int:		time interval between samplings
+ * @regions_update_int:	time interval between target regions update
  * @aggr_int:		time interval between aggregations
  * @min_nr_reg:		minimal number of regions
  * @max_nr_reg:		maximum number of regions
@@ -176,8 +177,8 @@ int damon_set_targets(struct damon_ctx *ctx,
  *
  * Return: 0 on success, negative error code otherwise.
  */
-int damon_set_attrs(struct damon_ctx *ctx,
-		    unsigned long sample_int, unsigned long aggr_int,
+int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
+		    unsigned long aggr_int, unsigned long regions_update_int,
 		    unsigned long min_nr_reg, unsigned long max_nr_reg)
 {
 	if (min_nr_reg < 3) {
@@ -193,6 +194,7 @@ int damon_set_attrs(struct damon_ctx *ctx,
 
 	ctx->sample_interval = sample_int;
 	ctx->aggr_interval = aggr_int;
+	ctx->regions_update_interval = regions_update_int;
 	ctx->min_nr_regions = min_nr_reg;
 	ctx->max_nr_regions = max_nr_reg;
 
@@ -529,6 +531,17 @@ static void kdamond_split_regions(struct damon_ctx *ctx)
 	last_nr_regions = nr_regions;
 }
 
+/*
+ * Check whether it is time to check and apply the target monitoring regions
+ *
+ * Returns true if it is.
+ */
+static bool kdamond_need_update_regions(struct damon_ctx *ctx)
+{
+	return damon_check_reset_time_interval(&ctx->last_regions_update,
+			ctx->regions_update_interval);
+}
+
 /*
  * Check whether current monitoring should be stopped
  *
@@ -612,6 +625,11 @@ static int kdamond_fn(void *data)
 			kdamond_reset_aggregated(ctx);
 			kdamond_split_regions(ctx);
 		}
+
+		if (kdamond_need_update_regions(ctx)) {
+			kdamond_call_prmt(ctx, update_target_regions);
+			sz_limit = damon_region_sz_limit(ctx);
+		}
 	}
 	damon_for_each_target(t, ctx) {
 		damon_for_each_region_safe(r, next, t)
-- 
2.17.1