mm/zswap: delay the initializaton of zswap until the first enablement

hulk inclusion
category: performance
bugzilla: 187468, https://gitee.com/openeuler/kernel/issues/I61HSG

--------------------------------

The zswap initialization consumes some memory. If we don't use zswap,
there's no need to initial it. So delay the initializaton of zswap until
the first enablement.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>

mm/zswap.c

@@ -79,6 +79,8 @@ static bool zswap_pool_reached_full;
 
 #define ZSWAP_PARAM_UNSET ""
 
+static int zswap_setup(void);
+
 /* Enable/disable zswap */
 static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
 static int zswap_enabled_param_set(const char *,
@@ -209,6 +211,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);
 
 /* init state */
 static int zswap_init_state;
+/* used to ensure the integrity of initialization */
+static DEFINE_MUTEX(zswap_init_lock);
 
 /* init completed, but couldn't create the initial pool */
 static bool zswap_has_pool;
@@ -767,11 +771,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
 	if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
 		return 0;
 
-	/* if this is load-time (pre-init) param setting,
+	/*
+	 * if zswap has not been initialized,
 	 * don't create a pool; that's done during init.
 	 */
-	if (zswap_init_state == ZSWAP_UNINIT)
-		return param_set_charp(s, kp);
+	mutex_lock(&zswap_init_lock);
+	if (zswap_init_state == ZSWAP_UNINIT) {
+		ret = param_set_charp(s, kp);
+		mutex_unlock(&zswap_init_lock);
+		return ret;
+	}
+	mutex_unlock(&zswap_init_lock);
 
 	if (!type) {
 		if (!zpool_has_pool(s)) {
@@ -861,6 +871,14 @@ static int zswap_zpool_param_set(const char *val,
 static int zswap_enabled_param_set(const char *val,
 				   const struct kernel_param *kp)
 {
+	if (system_state == SYSTEM_RUNNING) {
+		mutex_lock(&zswap_init_lock);
+		if (zswap_setup()) {
+			mutex_unlock(&zswap_init_lock);
+			return -ENODEV;
+		}
+		mutex_unlock(&zswap_init_lock);
+	}
 	if (zswap_init_state == ZSWAP_INIT_FAILED) {
 		pr_err("can't enable, initialization failed\n");
 		return -ENODEV;
@@ -1435,14 +1453,14 @@ static int __init zswap_debugfs_init(void)
 static void __exit zswap_debugfs_exit(void) { }
 #endif
 
-/*********************************
-* module init and exit
-**********************************/
-static int __init init_zswap(void)
+static int zswap_setup(void)
 {
 	struct zswap_pool *pool;
 	int ret;
 
+	if (zswap_init_state != ZSWAP_UNINIT)
+		return 0;
+
 	if (zswap_entry_cache_create()) {
 		pr_err("entry cache creation failed\n");
 		goto cache_fail;
@@ -1496,6 +1514,18 @@ static int __init init_zswap(void)
 	zswap_enabled = false;
 	return -ENOMEM;
 }
+
+/*********************************
+* module init and exit
+**********************************/
+static int __init init_zswap(void)
+{
+	/* skip init if zswap is disabled when system startup */
+	if (!zswap_enabled)
+		return 0;
+	return zswap_setup();
+}
+
 /* must be late so crypto has time to come up */
 late_initcall(init_zswap);