linux-kernel - [RFC PATCH v3 02/13] mm/damon/core: add damos->migrate

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Message-ID: <20250702201337.5780-3-bijan311@gmail.com>
Date: Wed,  2 Jul 2025 15:13:25 -0500
From: Bijan Tabatabai <bijan311@...il.com>
To: damon@...ts.linux.dev,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Cc: sj@...nel.org,
	akpm@...ux-foundation.org,
	corbet@....net,
	joshua.hahnjy@...il.com,
	bijantabatab@...ron.com,
	venkataravis@...ron.com,
	emirakhur@...ron.com,
	ajayjoshi@...ron.com,
	vtavarespetr@...ron.com
Subject: [RFC PATCH v3 02/13] mm/damon/core: add damos->migrate_dests field

From: SeongJae Park <sj@...nel.org>

Add a new field to 'struct damos', namely migrate_dests, to allow DAMON
API callers specify multiple migration destination nodes and their
weights.  Also update 'struct damos' creation and destruction functions
accordingly to initialize the new field and free up the API
caller-allocated buffers on those, respectively.

Signed-off-by: SeongJae Park <sj@...nel.org>
Signed-off-by: Bijan Tabatabai <bijantabatab@...ron.com>
---
 include/linux/damon.h | 13 ++++++++++---
 mm/damon/core.c       |  4 ++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 24d387a972dd..6f0b0806236d 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -470,6 +470,7 @@ struct damos_migrate_dests {
  * @apply_interval_us:	The time between applying the @action.
  * @quota:		Control the aggressiveness of this scheme.
  * @wmarks:		Watermarks for automated (in)activation of this scheme.
+ * @migrate_dests:	Destination nodes if @action is "migrate_{hot,cold}".
  * @target_nid:		Destination node if @action is "migrate_{hot,cold}".
  * @filters:		Additional set of &struct damos_filter for &action.
  * @ops_filters:	ops layer handling &struct damos_filter objects list.
@@ -488,9 +489,12 @@ struct damos_migrate_dests {
  * monitoring context are inactive, DAMON stops monitoring either, and just
  * repeatedly checks the watermarks.
  *
+ * @migrate_dests specifies multiple migration target nodes with different
+ * weights for migrate_hot or migrate_cold actions.  @target_nid is ignored if
+ * this is set.
+ *
  * @target_nid is used to set the migration target node for migrate_hot or
- * migrate_cold actions, which means it's only meaningful when @action is either
- * "migrate_hot" or "migrate_cold".
+ * migrate_cold actions, and @migrate_dests is unset.
  *
  * Before applying the &action to a memory region, &struct damon_operations
  * implementation could check pages of the region and skip &action to respect
@@ -533,7 +537,10 @@ struct damos {
 	struct damos_quota quota;
 	struct damos_watermarks wmarks;
 	union {
-		int target_nid;
+		struct {
+			int target_nid;
+			struct damos_migrate_dests migrate_dests;
+		};
 	};
 	struct list_head filters;
 	struct list_head ops_filters;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index bc2e58c1222d..a4c3cfe531df 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -407,6 +407,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	scheme->wmarks = *wmarks;
 	scheme->wmarks.activated = true;
 
+	scheme->migrate_dests = (struct damos_migrate_dests){};
 	scheme->target_nid = target_nid;
 
 	return scheme;
@@ -449,6 +450,9 @@ void damon_destroy_scheme(struct damos *s)
 
 	damos_for_each_filter_safe(f, next, s)
 		damos_destroy_filter(f);
+
+	kfree(s->migrate_dests.node_id_arr);
+	kfree(s->migrate_dests.weight_arr);
 	damon_del_scheme(s);
 	damon_free_scheme(s);
 }
-- 
2.43.5