[RFC PATCH 03/11] mm/damon/reclaim: add a parameter called skip_anon for avoiding anonymous pages reclamation

[SeongJae Park <sj@kernel.org>]

In some cases, for example if users have confidence at anonymous pages
management or the swap device is too slow, users would want to avoid
DAMON_RECLAIM swapping the anonymous pages out.  For such case, add yet
another DAMON_RECLAIM parameter, namely 'skip_anon'.  When it is set as
'Y', DAMON_RECLAIM will avoid reclaiming anonymous pages using a DAMOS
filter.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/reclaim.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index e82631f39481..648d2a85523a 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -98,6 +98,15 @@ module_param(monitor_region_start, ulong, 0600);
 static unsigned long monitor_region_end __read_mostly;
 module_param(monitor_region_end, ulong, 0600);
 
+/*
+ * Skip anonymous pages reclamation.
+ *
+ * If this parameter is set as ``Y``, DAMON_RECLAIM does not reclaim anonymous
+ * pages.  By default, ``N``.
+ */
+static bool skip_anon __read_mostly;
+module_param(skip_anon, bool, 0600);
+
 /*
  * PID of the DAMON thread
  *
@@ -142,6 +151,7 @@ static struct damos *damon_reclaim_new_scheme(void)
 static int damon_reclaim_apply_parameters(void)
 {
 	struct damos *scheme;
+	struct damos_filter *filter;
 	int err = 0;
 
 	err = damon_set_attrs(ctx, &damon_reclaim_mon_attrs);
@@ -152,6 +162,15 @@ static int damon_reclaim_apply_parameters(void)
 	scheme = damon_reclaim_new_scheme();
 	if (!scheme)
 		return -ENOMEM;
+	if (skip_anon) {
+		filter = damos_new_filter(DAMOS_FILTER_TYPE_ANON, true);
+		if (!filter) {
+			/* Will be freed by next 'damon_set_schemes()' below */
+			damon_destroy_scheme(scheme);
+			return -ENOMEM;
+		}
+		damos_add_filter(scheme, filter);
+	}
 	damon_set_schemes(ctx, &scheme, 1);
 
 	return damon_set_region_biggest_system_ram_default(target,
-- 
2.25.1