Implement the DAMON-based working set size estimation logic.  The logic
simply iterates memory regions in DAMON-generated access pattern
snapshot for every aggregation, and get the total sum of the size of any
region having one or higher 'nr_accesses' count.  That is, it assumes
any region having one or higher 'nr_accesses' to be a part of the
working set.  The estimated value is printed to the kernel log.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 samples/damon/wsse.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
index 119ac8a2c901..a2a94c505938 100644
--- a/samples/damon/wsse.c
+++ b/samples/damon/wsse.c
@@ -30,6 +30,23 @@ MODULE_PARM_DESC(enable, "Enable or disable DAMON_SAMPLE_WSSE");
 static struct damon_ctx *ctx;
 static struct pid *target_pidp;
 
+static int damon_sample_wsse_after_aggregate(struct damon_ctx *c)
+{
+	struct damon_target *t;
+
+	damon_for_each_target(t, c) {
+		struct damon_region *r;
+		unsigned long wss = 0;
+
+		damon_for_each_region(r, t) {
+			if (r->nr_accesses > 0)
+				wss += r->ar.end - r->ar.start;
+		}
+		pr_info("wss: %lu\n", wss);
+	}
+	return 0;
+}
+
 static int damon_sample_wsse_start(void)
 {
 	struct damon_target *target;
@@ -57,6 +74,7 @@ static int damon_sample_wsse_start(void)
 	}
 	target->pid = target_pidp;
 
+	ctx->callback.after_aggregation = damon_sample_wsse_after_aggregate;
 	return damon_start(&ctx, 1, true);
 }
 
-- 
2.39.5