[RFC] restore user defined min_free_kbytes when disabling thp

[Han Pingtian]

The testcase 'thp04' of LTP will enable THP, do some testing, then
disable it if it wasn't enabled. But this will leave a different value
of min_free_kbytes if it has been set by admin. So I think it's better
to restore the user defined value after disabling THP.

---

thp increases the value of min_free_kbytes in initialization. This will
change the user defined value of min_free_kbytes. So try to restore the
value when disabling thp.

Signed-off-by: Han Pingtian <hanpt@xxxxxxxxxxxxxxxxxx>
---
 mm/huge_memory.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94a824f..276180b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -164,6 +164,15 @@ static int start_khugepaged(void)
 	} else if (khugepaged_thread) {
 		kthread_stop(khugepaged_thread);
 		khugepaged_thread = NULL;
+
+		if (user_min_free_kbytes >= 0) {
+			pr_info("restore min_free_kbytes from %d to user "
+				"defined %d when stopping khugepaged\n",
+				min_free_kbytes, user_min_free_kbytes);
+
+			min_free_kbytes = user_min_free_kbytes;
+			setup_per_zone_wmarks();
+		}
 	}
 
 	return err;
-- 
1.7.7.6

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