[PATCH v3 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[gutierrez.asier]

From: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>

Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new
DAMOS quota goal metric to measure the amount of huge page
consumption to total memory consumption ratio.

Vmstat may lag, which in some cases may lead to NR_FREE_PAGES
being equal to the amount of RAM in the system. A guard is added
to avoid the extremely unlikely case of a division by 0.[1] In that
we return INT_MAX, which should be enough not to apply any DAMOS
action until the NR_FREE_PAGES is updated.

[1] https://lore.kernel.org/all/20260715151615.99767-1-sj@xxxxxxxxxx/

Signed-off-by: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 327f534696aa..0d0b7bb233b7 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -153,6 +153,7 @@ enum damos_action {
  * @DAMOS_QUOTA_INACTIVE_MEM_BP:	Inactive to total LRU memory ratio.
  * @DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP:	Scheme-eligible memory ratio of a
  *					node in basis points (0-10000).
+ * @DAMOS_QUOTA_HUGEPAGE_MEM_BP:	Huge page to total used memory ratio.
  * @NR_DAMOS_QUOTA_GOAL_METRICS:	Number of DAMOS quota goal metrics.
  *
  * Metrics equal to larger than @NR_DAMOS_QUOTA_GOAL_METRICS are unsupported.
@@ -167,6 +168,7 @@ enum damos_quota_goal_metric {
 	DAMOS_QUOTA_ACTIVE_MEM_BP,
 	DAMOS_QUOTA_INACTIVE_MEM_BP,
 	DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
+	DAMOS_QUOTA_HUGEPAGE_MEM_BP,
 	NR_DAMOS_QUOTA_GOAL_METRICS,
 };
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 603b102ff80f..73aaee43c6f7 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3004,6 +3004,24 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
 	return mult_frac(inactive, 10000, total);
 }
 
+static unsigned int damos_hugepage_mem_bp(void)
+{
+	unsigned long thp, total;
+
+	thp = global_node_page_state(NR_ANON_THPS) +
+				global_node_page_state(NR_SHMEM_THPS) +
+				global_node_page_state(NR_FILE_THPS);
+	total = totalram_pages() - global_zone_page_state(NR_FREE_PAGES);
+
+	/*
+	 * vmstat may lag in idle systems and lead to free pages equaling to
+	 * the total RAM in the system.
+	 */
+	if (!total)
+		return INT_MAX;
+	return mult_frac(thp, 10000, total);
+}
+
 static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 		struct damos *s, struct damos_quota_goal *goal)
 {
@@ -3035,6 +3053,9 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 		goal->current_value = damos_get_node_eligible_mem_bp(c, s,
 				goal->nid);
 		break;
+	case DAMOS_QUOTA_HUGEPAGE_MEM_BP:
+		goal->current_value = damos_hugepage_mem_bp();
+		break;
 	default:
 		break;
 	}
-- 
2.43.0