mm/damon/schemes: implement statistics feature

To tune the DAMON-based operation schemes, knowing how many and how
large regions are affected by each of the schemes will be helful.  Those
stats could be used for not only the tuning, but also monitoring of the
working set size and the number of regions, if the scheme does not
change the program behavior too much.

For the reason, this implements the statistics for the schemes.  The
total number and size of the regions that each scheme is applied are
exported to users via '->stat_count' and '->stat_sz' of 'struct damos'.
Admins can also check the number by reading 'schemes' debugfs file.  The
last two integers now represents the stats.  To allow collecting the
stats without changing the program behavior, this also adds new scheme
action, 'DAMOS_STAT'.  Note that 'DAMOS_STAT' is not only making no
memory operation actions, but also does not reset the age of regions.

Link: https://lkml.kernel.org/r/20211001125604.29660-6-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 Rienjes <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>

3 files changed, 11 insertions, 3 deletions

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 0ed97b21cbb6..2f6785737902 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -103,6 +103,8 @@ struct damos *damon_new_scheme(
 	scheme->min_age_region = min_age_region;
 	scheme->max_age_region = max_age_region;
 	scheme->action = action;
+	scheme->stat_count = 0;
+	scheme->stat_sz = 0;
 	INIT_LIST_HEAD(&scheme->list);
 
 	return scheme;
@@ -544,9 +546,12 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			continue;
 		if (r->age < s->min_age_region || s->max_age_region < r->age)
 			continue;
+		s->stat_count++;
+		s->stat_sz += sz;
 		if (c->primitive.apply_scheme)
 			c->primitive.apply_scheme(c, t, r, s);
-		r->age = 0;
+		if (s->action != DAMOS_STAT)
+			r->age = 0;
 	}
 }
 
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 78b7a04490c5..28d6abf27763 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -106,11 +106,11 @@ static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 
 	damon_for_each_scheme(s, c) {
 		rc = scnprintf(&buf[written], len - written,
-				"%lu %lu %u %u %u %u %d\n",
+				"%lu %lu %u %u %u %u %d %lu %lu\n",
 				s->min_sz_region, s->max_sz_region,
 				s->min_nr_accesses, s->max_nr_accesses,
 				s->min_age_region, s->max_age_region,
-				s->action);
+				s->action, s->stat_count, s->stat_sz);
 		if (!rc)
 			return -ENOMEM;
 
@@ -159,6 +159,7 @@ static bool damos_action_valid(int action)
 	case DAMOS_PAGEOUT:
 	case DAMOS_HUGEPAGE:
 	case DAMOS_NOHUGEPAGE:
+	case DAMOS_STAT:
 		return true;
 	default:
 		return false;
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 3e1c74d36bab..953c145b4f08 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -705,6 +705,8 @@ int damon_va_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
 	case DAMOS_NOHUGEPAGE:
 		madv_action = MADV_NOHUGEPAGE;
 		break;
+	case DAMOS_STAT:
+		return 0;
 	default:
 		pr_warn("Wrong action %d\n", scheme->action);
 		return -EINVAL;