Re: [PATCH 0/2] mm: thp: reduce unnecessary start_stop_khugepaged() calls

[Kiryl Shutsemau <kas@kernel.org>]

On Wed, Mar 04, 2026 at 02:22:32AM -0800, Breno Leitao wrote:
> Breno Leitao (2):
>       mm: thp: avoid calling start_stop_khugepaged() in anon_enabled_store()
>       mm: thp: avoid calling start_stop_khugepaged() in enabled_store()

I think the same can be achieved cleaner from within start_stop_khugepaged().

Completely untested patch is below.

One noticeable difference that with the patch we don't kick
khugepaged_wait if khugepaged_thread is there. But I don't think it
should make a difference.

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1dd3cfca610d..80f818d3a094 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2683,18 +2683,18 @@ static void set_recommended_min_free_kbytes(void)
 
 int start_stop_khugepaged(void)
 {
-	int err = 0;
+	guard(mutex)(&khugepaged_mutex);
+
+	/* Check if anything has to be done */
+	if (hugepage_pmd_enabled() == !!khugepaged_thread)
+		return 0;
 
-	mutex_lock(&khugepaged_mutex);
 	if (hugepage_pmd_enabled()) {
-		if (!khugepaged_thread)
-			khugepaged_thread = kthread_run(khugepaged, NULL,
-							"khugepaged");
+		khugepaged_thread = kthread_run(khugepaged, NULL, "khugepaged");
 		if (IS_ERR(khugepaged_thread)) {
 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
-			err = PTR_ERR(khugepaged_thread);
 			khugepaged_thread = NULL;
-			goto fail;
+			return PTR_ERR(khugepaged_thread);
 		}
 
 		if (!list_empty(&khugepaged_scan.mm_head))
@@ -2703,10 +2703,9 @@ int start_stop_khugepaged(void)
 		kthread_stop(khugepaged_thread);
 		khugepaged_thread = NULL;
 	}
+
 	set_recommended_min_free_kbytes();
-fail:
-	mutex_unlock(&khugepaged_mutex);
-	return err;
+	return 0;
 }
 
 void khugepaged_min_free_kbytes_update(void)
-- 
  Kiryl Shutsemau / Kirill A. Shutemov