[PATCH v3 1/2] mm: shmem: refactor thpsize_shmem_enabled_store() with sysfs_match_string()

[ranxiaokai627]

From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>

Inspired by commit 82d9ff648c6c ("mm: huge_memory: refactor
anon_enabled_store() with set_anon_enabled_mode()"), refactor
thpsize_shmem_enabled_store() using sysfs_match_string().
This eliminates the duplicated spin_lock/unlock(), set/clear_bit(),
calls across all branches, reducing code duplication.

Behavioral change:
Call start_stop_khugepaged() only when the mode actually changes.
If unchanged, call set_recommended_min_free_kbytes() to preserve
legacy watermark behavior. This avoids unnecessary khugepaged restarts.

Tested with selftests ./run_kselftest.sh -t mm:ksft_thp.sh,
all test cases passed.

Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
---
 mm/shmem.c | 107 ++++++++++++++++++++++++++++++-----------------------
 1 file changed, 60 insertions(+), 47 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 3b5dc21b323c..46d2cfc30823 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5526,6 +5526,29 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
 struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
 static DEFINE_SPINLOCK(huge_shmem_orders_lock);
 
+enum huge_shmem_enabled_mode {
+	HUGE_SHMEM_ENABLED_ALWAYS = 0,
+	HUGE_SHMEM_ENABLED_INHERIT,
+	HUGE_SHMEM_ENABLED_WITHIN_SIZE,
+	HUGE_SHMEM_ENABLED_ADVISE,
+	HUGE_SHMEM_ENABLED_NEVER,
+};
+
+static const char * const huge_shmem_enabled_mode_strings[] = {
+	[HUGE_SHMEM_ENABLED_ALWAYS]      = "always",
+	[HUGE_SHMEM_ENABLED_INHERIT]     = "inherit",
+	[HUGE_SHMEM_ENABLED_WITHIN_SIZE] = "within_size",
+	[HUGE_SHMEM_ENABLED_ADVISE]      = "advise",
+	[HUGE_SHMEM_ENABLED_NEVER]       = "never",
+};
+
+static unsigned long * const huge_shmem_orders_by_mode[] = {
+	[HUGE_SHMEM_ENABLED_ALWAYS]      = &huge_shmem_orders_always,
+	[HUGE_SHMEM_ENABLED_INHERIT]     = &huge_shmem_orders_inherit,
+	[HUGE_SHMEM_ENABLED_WITHIN_SIZE] = &huge_shmem_orders_within_size,
+	[HUGE_SHMEM_ENABLED_ADVISE]      = &huge_shmem_orders_madvise,
+};
+
 static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
 					  struct kobj_attribute *attr, char *buf)
 {
@@ -5546,63 +5569,53 @@ static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
 	return sysfs_emit(buf, "%s\n", output);
 }
 
+static bool set_shmem_enabled_mode(int order, enum huge_shmem_enabled_mode mode)
+{
+	bool changed = false;
+	enum huge_shmem_enabled_mode idx;
+
+	spin_lock(&huge_shmem_orders_lock);
+	for (idx = 0; idx < ARRAY_SIZE(huge_shmem_orders_by_mode); idx++) {
+		if (idx == mode)
+			changed |= !__test_and_set_bit(order, huge_shmem_orders_by_mode[idx]);
+		else
+			changed |= __test_and_clear_bit(order, huge_shmem_orders_by_mode[idx]);
+	}
+	spin_unlock(&huge_shmem_orders_lock);
+
+	return changed;
+}
+
 static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
 					   struct kobj_attribute *attr,
 					   const char *buf, size_t count)
 {
 	int order = to_thpsize(kobj)->order;
-	ssize_t ret = count;
-
-	if (sysfs_streq(buf, "always")) {
-		spin_lock(&huge_shmem_orders_lock);
-		clear_bit(order, &huge_shmem_orders_inherit);
-		clear_bit(order, &huge_shmem_orders_madvise);
-		clear_bit(order, &huge_shmem_orders_within_size);
-		set_bit(order, &huge_shmem_orders_always);
-		spin_unlock(&huge_shmem_orders_lock);
-	} else if (sysfs_streq(buf, "inherit")) {
-		/* Do not override huge allocation policy with non-PMD sized mTHP */
-		if (shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
-			return -EINVAL;
+	int mode;
 
-		spin_lock(&huge_shmem_orders_lock);
-		clear_bit(order, &huge_shmem_orders_always);
-		clear_bit(order, &huge_shmem_orders_madvise);
-		clear_bit(order, &huge_shmem_orders_within_size);
-		set_bit(order, &huge_shmem_orders_inherit);
-		spin_unlock(&huge_shmem_orders_lock);
-	} else if (sysfs_streq(buf, "within_size")) {
-		spin_lock(&huge_shmem_orders_lock);
-		clear_bit(order, &huge_shmem_orders_always);
-		clear_bit(order, &huge_shmem_orders_inherit);
-		clear_bit(order, &huge_shmem_orders_madvise);
-		set_bit(order, &huge_shmem_orders_within_size);
-		spin_unlock(&huge_shmem_orders_lock);
-	} else if (sysfs_streq(buf, "advise")) {
-		spin_lock(&huge_shmem_orders_lock);
-		clear_bit(order, &huge_shmem_orders_always);
-		clear_bit(order, &huge_shmem_orders_inherit);
-		clear_bit(order, &huge_shmem_orders_within_size);
-		set_bit(order, &huge_shmem_orders_madvise);
-		spin_unlock(&huge_shmem_orders_lock);
-	} else if (sysfs_streq(buf, "never")) {
-		spin_lock(&huge_shmem_orders_lock);
-		clear_bit(order, &huge_shmem_orders_always);
-		clear_bit(order, &huge_shmem_orders_inherit);
-		clear_bit(order, &huge_shmem_orders_within_size);
-		clear_bit(order, &huge_shmem_orders_madvise);
-		spin_unlock(&huge_shmem_orders_lock);
-	} else {
-		ret = -EINVAL;
-	}
+	mode = sysfs_match_string(huge_shmem_enabled_mode_strings, buf);
+	if (mode < 0)
+		return mode;
 
-	if (ret > 0) {
-		int err = start_stop_khugepaged();
+	/* Do not override huge allocation policy with non-PMD sized mTHP */
+	if (mode == HUGE_SHMEM_ENABLED_INHERIT &&
+	    shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
+		return -EINVAL;
 
+	if (set_shmem_enabled_mode(order, mode)) {
+		int err = start_stop_khugepaged();
 		if (err)
-			ret = err;
+			return err;
+	} else {
+		/*
+		 * Recalculate watermarks even when the mode hasn't changed
+		 * to preserve the legacy behavior, as this is always called
+		 * inside start_stop_khugepaged().
+		 */
+		set_recommended_min_free_kbytes();
 	}
-	return ret;
+
+	return count;
 }
 
 struct kobj_attribute thpsize_shmem_enabled_attr =
-- 
2.25.1