[RFC PATCH v2 7/9] mm/damon/core: set damos_filter default allowance behavior based on installed filters

[SeongJae Park <sj@kernel.org>]

Decide whether to allow or reject by default on core and opertions layer
handled filters evaluation stages.  It is decided as the opposite of the
last installed filter's behavior.  If there is no filter at all, allow
by default.  If there is any operations layer handled filters, core
layer's filtering stage sets allowing as the default behavior regardless
of the last filter of core layer-handling ones, since the last filter of
core layer handled filters in the case is not really the last filter of
the entire filtering stage.

Also, make the core layer's DAMOS filters handling stage uses the newly
set behavior field.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 78126a5145fd..8661f64ab1b4 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -864,6 +864,32 @@ static int damos_commit_ops_filters(struct damos *dst, struct damos *src)
 	return 0;
 }
 
+/**
+ * damos_filters_default_reject() - decide whether to reject memory that didn't
+ *				    match with any given filter.
+ * @filters:	Given DAMOS filters of a group.
+ */
+static bool damos_filters_default_reject(struct list_head *filters)
+{
+	struct damos_filter *last_filter;
+
+	if (list_empty(filters))
+		return false;
+	last_filter = list_last_entry(filters, struct damos_filter, list);
+	return last_filter->allow;
+}
+
+static void damos_set_filters_default_reject(struct damos *s)
+{
+	if (!list_empty(&s->ops_filters))
+		s->core_filters_default_reject = false;
+	else
+		s->core_filters_default_reject =
+			damos_filters_default_reject(&s->filters);
+	s->ops_filters_default_reject =
+		damos_filters_default_reject(&s->ops_filters);
+}
+
 static int damos_commit_filters(struct damos *dst, struct damos *src)
 {
 	int err;
@@ -871,7 +897,11 @@ static int damos_commit_filters(struct damos *dst, struct damos *src)
 	err = damos_commit_core_filters(dst, src);
 	if (err)
 		return err;
-	return damos_commit_ops_filters(dst, src);
+	err = damos_commit_ops_filters(dst, src);
+	if (err)
+		return err;
+	damos_set_filters_default_reject(dst);
+	return 0;
 }
 
 static struct damos *damon_nth_scheme(int n, struct damon_ctx *ctx)
@@ -1490,7 +1520,7 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
 		if (damos_filter_match(ctx, t, r, filter))
 			return !filter->allow;
 	}
-	return false;
+	return s->core_filters_default_reject;
 }
 
 /*
-- 
2.39.5