[PATCH] mm, thp: display [never] for defrag when THP is set to never

[Yuanhe Shu <xiangzao@xxxxxxxxxxxxxxxxx>]

When transparent_hugepage is set to never by cmdline or echo, defrag
still show what it used to be and can be modified which makes user
confusing whether defrag would take effect.

Actually if transparent_hugepage is set to never, defrag will not take
effect. Just Display never and remain unchangeable to for defrag when
transparent_hugepage is set to never.

Suggested-by: Liu Song <liusong@xxxxxxxxxxxxxxxxx>
Signed-off-by: Yuanhe Shu <xiangzao@xxxxxxxxxxxxxxxxx>
---
 mm/huge_memory.c | 38 ++++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94c958f7ebb5..03cd22a87b93 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -349,21 +349,25 @@ static ssize_t defrag_show(struct kobject *kobj,
 {
 	const char *output;
 
-	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
-		     &transparent_hugepage_flags))
-		output = "[always] defer defer+madvise madvise never";
-	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
-			  &transparent_hugepage_flags))
-		output = "always [defer] defer+madvise madvise never";
-	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG,
-			  &transparent_hugepage_flags))
-		output = "always defer [defer+madvise] madvise never";
-	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
-			  &transparent_hugepage_flags))
-		output = "always defer defer+madvise [madvise] never";
-	else
+	if (!test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags) &&
+	    !test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
 		output = "always defer defer+madvise madvise [never]";
-
+	else {
+		if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
+			&transparent_hugepage_flags))
+			output = "[always] defer defer+madvise madvise never";
+		else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
+				&transparent_hugepage_flags))
+			output = "always [defer] defer+madvise madvise never";
+		else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG,
+				&transparent_hugepage_flags))
+			output = "always defer [defer+madvise] madvise never";
+		else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
+				&transparent_hugepage_flags))
+			output = "always defer defer+madvise [madvise] never";
+		else
+			output = "always defer defer+madvise madvise [never]";
+	}
 	return sysfs_emit(buf, "%s\n", output);
 }
 
@@ -371,6 +375,12 @@ static ssize_t defrag_store(struct kobject *kobj,
 			    struct kobj_attribute *attr,
 			    const char *buf, size_t count)
 {
+	if (!test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags) &&
+	    !test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags)) {
+		pr_warn("transparent_hugepage not enabled, defrag takes no effect\n");
+		return -EINVAL;
+	}
+
 	if (sysfs_streq(buf, "always")) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
-- 
2.39.3