[PATCH] mm/damon: respect core layer filters' allowance decision on ops layer

[SeongJae Park <sj@kernel.org>]

Filtering decisions are made in filters evaluation order.  Once a
decision is made by a filter, filters that scheduled to be evaluated
after the decision-made filter should just respect it.  This is the
intended and documented behavior.  Since core layer-handled filters are
evaluated before operations layer-handled filters, decisions made on
core layer should respected by ops layer.

In case of reject filters, the decision is respected, since core
layer-rejected regions are not passed to ops layer.  But in case of
allow filters, ops layer filters don't know if the region has passed to
them because it was allowed by core filters or just because it didn't
match to any core layer.  The current wrong implementation assumes it
was due to not matched by any core filters.  As a reuslt, the decision
is not respected.  Pass the missing information to ops layer using a new
filed in 'struct damos', and make the ops layer filters respect it.

Fixes: 491fee286e56 ("mm/damon/core: support damos_filter->allow")
Cc: <stable@vger.kernel.org> # 6.14.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 5 +++++
 mm/damon/core.c       | 6 +++++-
 mm/damon/paddr.c      | 3 +++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 795ca09b1107..242910b190c9 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -496,6 +496,11 @@ struct damos {
 	unsigned long next_apply_sis;
 	/* informs if ongoing DAMOS walk for this scheme is finished */
 	bool walk_completed;
+	/*
+	 * If the current region in the filtering stage is allowed by core
+	 * layer-handled filters.  If true, operations layer allows it, too.
+	 */
+	bool core_filters_allowed;
 /* public: */
 	struct damos_quota quota;
 	struct damos_watermarks wmarks;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index cfa105ee9610..b1ce072b56f2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1433,9 +1433,13 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
 {
 	struct damos_filter *filter;
 
+	s->core_filters_allowed = false;
 	damos_for_each_filter(filter, s) {
-		if (damos_filter_match(ctx, t, r, filter))
+		if (damos_filter_match(ctx, t, r, filter)) {
+			if (filter->allow)
+				s->core_filters_allowed = true;
 			return !filter->allow;
+		}
 	}
 	return false;
 }
diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 25090230da17..d5db313ca717 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -253,6 +253,9 @@ static bool damos_pa_filter_out(struct damos *scheme, struct folio *folio)
 {
 	struct damos_filter *filter;
 
+	if (scheme->core_filters_allowed)
+		return false;
+
 	damos_for_each_filter(filter, scheme) {
 		if (damos_pa_filter_match(filter, folio))
 			return !filter->allow;

base-commit: c8f5534db6574708eee17fcd416f0a3fb3b45dbd
-- 
2.39.5