[PATCH v16 05/14] mm/damon: Allow dynamic monitoring target regions update

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

The monitoring target regions can be dynamically changed.  For example,
virtual memory mapping could be dynamically updated and physical memory
could be hot-plugged.

To handle such cases, this commit adds a monitoring attribute, ``regions
update interval`` and a callback ``init_target_regions`` in the
monitoring context.  If the two fields are properly set, DAMON will call
the ``init_target_regions()`` callback for every ``regions update
interval``.  In the callback, users can check current memory mapping or
hotplugged physical memory sections and appropriately update the
monitoring target regions of the context.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 include/linux/damon.h | 20 +++++++++++++++-----
 mm/damon.c            | 23 +++++++++++++++++++++--
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 9588bc162c3a..aa14d4e910e5 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -64,13 +64,16 @@ struct damon_task {
  *
  * @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 number of initial 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.
@@ -88,6 +91,7 @@ struct damon_task {
  * @tasks_list:		Head of monitoring target tasks (&damon_task) list.
  *
  * @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.
  * @sample_cb:			Called for each sampling interval.
@@ -96,11 +100,14 @@ struct damon_task {
  * DAMON can be extended for various address spaces by users.  For this, users
  * can register the target address space dependent low level functions for
  * their usecases via the callback pointers of the context.  The monitoring
- * thread calls @init_target_regions before starting the monitoring, and
+ * thread calls @init_target_regions before starting the monitoring,
+ * @update_target_regions for each @regions_update_interval, and
  * @prepare_access_checks and @check_accesses 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
@@ -115,10 +122,12 @@ struct damon_task {
 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;
@@ -128,6 +137,7 @@ struct damon_ctx {
 
 	/* callbacks */
 	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);
 	void (*sample_cb)(struct damon_ctx *context);
@@ -135,8 +145,8 @@ struct damon_ctx {
 };
 
 int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids);
-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_start(struct damon_ctx *ctx);
 int damon_stop(struct damon_ctx *ctx);
diff --git a/mm/damon.c b/mm/damon.c
index 5cf39b3ad222..a19ec17a35cb 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -385,6 +385,17 @@ 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
  *
@@ -455,6 +466,12 @@ static int kdamond_fn(void *data)
 			kdamond_reset_aggregated(ctx);
 			kdamond_split_regions(ctx);
 		}
+
+		if (kdamond_need_update_regions(ctx)) {
+			if (ctx->update_target_regions)
+				ctx->update_target_regions(ctx);
+			sz_limit = damon_region_sz_limit(ctx);
+		}
 	}
 	damon_for_each_task(t, ctx) {
 		damon_for_each_region_safe(r, next, t)
@@ -562,6 +579,7 @@ int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids)
  * 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
@@ -571,8 +589,8 @@ int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids)
  *
  * 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) {
@@ -588,6 +606,7 @@ 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;
 
-- 
2.17.1