huge_memory: add huge_zero_page_shrinker_(init|exit) function

Add huge_zero_page_shrinker_init() and huge_zero_page_shrinker_exit().
As shrinker will not be needed when static PMD zero page is enabled,
these two functions can be a no-op.

This is a preparation patch for static PMD zero page. No functional
changes.

Signed-off-by: Pankaj Raghav <[email protected]>

Author: Panky-codes

mm/huge_memory.c

@@ -289,6 +289,24 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 }
 
 static struct shrinker *huge_zero_page_shrinker;
+static int huge_zero_page_shrinker_init(void)
+{
+	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
+	if (!huge_zero_page_shrinker)
+		return -ENOMEM;
+
+	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
+	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
+	shrinker_register(huge_zero_page_shrinker);
+	return 0;
+}
+
+static void huge_zero_page_shrinker_exit(void)
+{
+	shrinker_free(huge_zero_page_shrinker);
+	return;
+}
+
 
 #ifdef CONFIG_SYSFS
 static ssize_t enabled_show(struct kobject *kobj,
@@ -850,33 +868,31 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 
 static int __init thp_shrinker_init(void)
 {
-	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
-	if (!huge_zero_page_shrinker)
-		return -ENOMEM;
+	int ret = 0;
 
 	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
 						 SHRINKER_MEMCG_AWARE |
 						 SHRINKER_NONSLAB,
 						 "thp-deferred_split");
-	if (!deferred_split_shrinker) {
-		shrinker_free(huge_zero_page_shrinker);
+	if (!deferred_split_shrinker)
 		return -ENOMEM;
-	}
-
-	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
-	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
-	shrinker_register(huge_zero_page_shrinker);
 
 	deferred_split_shrinker->count_objects = deferred_split_count;
 	deferred_split_shrinker->scan_objects = deferred_split_scan;
 	shrinker_register(deferred_split_shrinker);
 
+	ret = huge_zero_page_shrinker_init();
+	if (ret) {
+		shrinker_free(deferred_split_shrinker);
+		return ret;
+	}
+
 	return 0;
 }
 
 static void __init thp_shrinker_exit(void)
 {
-	shrinker_free(huge_zero_page_shrinker);
+	huge_zero_page_shrinker_exit();
 	shrinker_free(deferred_split_shrinker);
 }