[PATCH v2 3/3] mm: huge_memory: refactor enabled_store() with change_enabled()

[Breno Leitao <leitao@debian.org>]

Refactor enabled_store() to use a new change_enabled() helper that
reuses the shared enum enabled_mode and enabled_mode_strings[]
introduced in the previous commit.

The helper uses the same loop pattern as change_anon_orders(),
iterating over an array of flag bit positions and using
test_and_set_bit()/test_and_clear_bit() to track whether the state
actually changed. ENABLED_INHERIT is rejected since it is not a
valid mode for the global THP setting.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/huge_memory.c | 51 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 15 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 19619213f54d1..dd5011cf36839 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -330,30 +330,51 @@ static const char * const enabled_mode_strings[] = {
 	[ENABLED_NEVER]		= "never",
 };
 
+static bool change_enabled(enum enabled_mode mode)
+{
+	static const unsigned long thp_flags[] = {
+		TRANSPARENT_HUGEPAGE_FLAG,
+		TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
+	};
+	bool changed = false;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(thp_flags); i++) {
+		if (i == mode)
+			changed |= !test_and_set_bit(thp_flags[i],
+						     &transparent_hugepage_flags);
+		else
+			changed |= test_and_clear_bit(thp_flags[i],
+						      &transparent_hugepage_flags);
+	}
+
+	return changed;
+}
+
 static ssize_t enabled_store(struct kobject *kobj,
 			     struct kobj_attribute *attr,
 			     const char *buf, size_t count)
 {
-	ssize_t ret = count;
+	int mode;
 
-	if (sysfs_streq(buf, "always")) {
-		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
-		set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
-	} else if (sysfs_streq(buf, "madvise")) {
-		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
-		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
-	} else if (sysfs_streq(buf, "never")) {
-		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
-		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
-	} else
-		ret = -EINVAL;
+	mode = sysfs_match_string(enabled_mode_strings, buf);
+	if (mode < 0 || mode == ENABLED_INHERIT)
+		return -EINVAL;
 
-	if (ret > 0) {
+	if (change_enabled(mode)) {
 		int err = start_stop_khugepaged();
+
 		if (err)
-			ret = err;
+			return err;
+	} else {
+		/*
+		 * Recalculate watermarks even when the mode didn't
+		 * change, as the previous code always called
+		 * start_stop_khugepaged() which does this internally.
+		 */
+		set_recommended_min_free_kbytes();
 	}
-	return ret;
+	return count;
 }
 
 static struct kobj_attribute enabled_attr = __ATTR_RW(enabled);

-- 
2.47.3