f2fs: introduce a shrinker for mounted fs

This patch introduces a shrinker targeting to reduce memory footprint consumed
by a number of in-memory f2fs data structures.

In addition, it newly adds:
 - sbi->umount_mutex to avoid data races on shrinker and put_super
 - sbi->shruinker_run_no to not revisit objects

Note that the basic implementation was copied from fs/ubifs/shrinker.c
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/Makefile

@@ -2,6 +2,7 @@ obj-$(CONFIG_F2FS_FS) += f2fs.o
 
 f2fs-y		:= dir.o file.o inode.o namei.o hash.o super.o inline.o
 f2fs-y		+= checkpoint.o gc.o data.o node.o segment.o recovery.o
+f2fs-y		+= shrinker.o
 f2fs-$(CONFIG_F2FS_STAT_FS) += debug.o
 f2fs-$(CONFIG_F2FS_FS_XATTR) += xattr.o
 f2fs-$(CONFIG_F2FS_FS_POSIX_ACL) += acl.o

fs/f2fs/f2fs.h

@@ -791,6 +791,11 @@ struct f2fs_sb_info {
 	/* For sysfs suppport */
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;
+
+	/* For shrinker support */
+	struct list_head s_list;
+	struct mutex umount_mutex;
+	unsigned int shrinker_run_no;
 };
 
 /*
@@ -1951,6 +1956,14 @@ bool f2fs_empty_inline_dir(struct inode *);
 int f2fs_read_inline_dir(struct file *, struct dir_context *,
 						struct f2fs_str *);
 
+/*
+ * shrinker.c
+ */
+unsigned long f2fs_shrink_count(struct shrinker *, struct shrink_control *);
+unsigned long f2fs_shrink_scan(struct shrinker *, struct shrink_control *);
+void f2fs_join_shrinker(struct f2fs_sb_info *);
+void f2fs_leave_shrinker(struct f2fs_sb_info *);
+
 /*
  * crypto support
  */

fs/f2fs/shrinker.c

+/*
+ * f2fs shrinker support
+ *   the basic infra was copied from fs/ubifs/shrinker.c
+ *
+ * Copyright (c) 2015 Motorola Mobility
+ * Copyright (c) 2015 Jaegeuk Kim <jaegeuk@kernel.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/fs.h>
+#include <linux/f2fs_fs.h>
+
+#include "f2fs.h"
+
+static LIST_HEAD(f2fs_list);
+static DEFINE_SPINLOCK(f2fs_list_lock);
+static unsigned int shrinker_run_no;
+
+unsigned long f2fs_shrink_count(struct shrinker *shrink,
+				struct shrink_control *sc)
+{
+	struct f2fs_sb_info *sbi;
+	struct list_head *p;
+	unsigned long count = 0;
+
+	spin_lock(&f2fs_list_lock);
+	p = f2fs_list.next;
+	while (p != &f2fs_list) {
+		sbi = list_entry(p, struct f2fs_sb_info, s_list);
+
+		/* stop f2fs_put_super */
+		if (!mutex_trylock(&sbi->umount_mutex)) {
+			p = p->next;
+			continue;
+		}
+		spin_unlock(&f2fs_list_lock);
+
+		/* TODO: count # of objects */
+
+		spin_lock(&f2fs_list_lock);
+		p = p->next;
+		mutex_unlock(&sbi->umount_mutex);
+	}
+	spin_unlock(&f2fs_list_lock);
+	return count;
+}
+
+unsigned long f2fs_shrink_scan(struct shrinker *shrink,
+				struct shrink_control *sc)
+{
+	unsigned long nr = sc->nr_to_scan;
+	struct f2fs_sb_info *sbi;
+	struct list_head *p;
+	unsigned int run_no;
+	unsigned long freed = 0;
+
+	spin_lock(&f2fs_list_lock);
+	do {
+		run_no = ++shrinker_run_no;
+	} while (run_no == 0);
+	p = f2fs_list.next;
+	while (p != &f2fs_list) {
+		sbi = list_entry(p, struct f2fs_sb_info, s_list);
+
+		if (sbi->shrinker_run_no == run_no)
+			break;
+
+		/* stop f2fs_put_super */
+		if (!mutex_trylock(&sbi->umount_mutex)) {
+			p = p->next;
+			continue;
+		}
+		spin_unlock(&f2fs_list_lock);
+
+		sbi->shrinker_run_no = run_no;
+
+		/* TODO: shrink caches */
+
+		spin_lock(&f2fs_list_lock);
+		p = p->next;
+		list_move_tail(&sbi->s_list, &f2fs_list);
+		mutex_unlock(&sbi->umount_mutex);
+		if (freed >= nr)
+			break;
+	}
+	spin_unlock(&f2fs_list_lock);
+	return freed;
+}
+
+void f2fs_join_shrinker(struct f2fs_sb_info *sbi)
+{
+	spin_lock(&f2fs_list_lock);
+	list_add_tail(&sbi->s_list, &f2fs_list);
+	spin_unlock(&f2fs_list_lock);
+}
+
+void f2fs_leave_shrinker(struct f2fs_sb_info *sbi)
+{
+	spin_lock(&f2fs_list_lock);
+	list_del(&sbi->s_list);
+	spin_unlock(&f2fs_list_lock);
+}

fs/f2fs/super.c

@@ -39,6 +39,13 @@ static struct proc_dir_entry *f2fs_proc_root;
 static struct kmem_cache *f2fs_inode_cachep;
 static struct kset *f2fs_kset;
 
+/* f2fs-wide shrinker description */
+static struct shrinker f2fs_shrinker_info = {
+	.scan_objects = f2fs_shrink_scan,
+	.count_objects = f2fs_shrink_count,
+	.seeks = DEFAULT_SEEKS,
+};
+
 enum {
 	Opt_gc_background,
 	Opt_disable_roll_forward,
@@ -500,6 +507,9 @@ static void f2fs_put_super(struct super_block *sb)
 
 	stop_gc_thread(sbi);
 
+	/* prevent remaining shrinker jobs */
+	mutex_lock(&sbi->umount_mutex);
+
 	/*
 	 * We don't need to do checkpoint when superblock is clean.
 	 * But, the previous checkpoint was not done by umount, it needs to do
@@ -523,6 +533,9 @@ static void f2fs_put_super(struct super_block *sb)
 	release_dirty_inode(sbi);
 	release_discard_addrs(sbi);
 
+	f2fs_leave_shrinker(sbi);
+	mutex_unlock(&sbi->umount_mutex);
+
 	iput(sbi->node_inode);
 	iput(sbi->meta_inode);
 
@@ -972,6 +985,9 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 
 	sbi->dir_level = DEF_DIR_LEVEL;
 	clear_sbi_flag(sbi, SBI_NEED_FSCK);
+
+	INIT_LIST_HEAD(&sbi->s_list);
+	mutex_init(&sbi->umount_mutex);
 }
 
 /*
@@ -1214,6 +1230,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 		goto free_nm;
 	}
 
+	f2fs_join_shrinker(sbi);
+
 	/* if there are nt orphan nodes free them */
 	recover_orphan_inodes(sbi);
 
@@ -1310,7 +1328,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	dput(sb->s_root);
 	sb->s_root = NULL;
 free_node_inode:
+	mutex_lock(&sbi->umount_mutex);
+	f2fs_leave_shrinker(sbi);
 	iput(sbi->node_inode);
+	mutex_unlock(&sbi->umount_mutex);
 free_nm:
 	destroy_node_manager(sbi);
 free_sm:
@@ -1406,13 +1427,20 @@ static int __init init_f2fs_fs(void)
 	err = f2fs_init_crypto();
 	if (err)
 		goto free_kset;
-	err = register_filesystem(&f2fs_fs_type);
+
+	err = register_shrinker(&f2fs_shrinker_info);
 	if (err)
 		goto free_crypto;
+
+	err = register_filesystem(&f2fs_fs_type);
+	if (err)
+		goto free_shrinker;
 	f2fs_create_root_stats();
 	f2fs_proc_root = proc_mkdir("fs/f2fs", NULL);
 	return 0;
 
+free_shrinker:
+	unregister_shrinker(&f2fs_shrinker_info);
 free_crypto:
 	f2fs_exit_crypto();
 free_kset:
@@ -1435,6 +1463,7 @@ static void __exit exit_f2fs_fs(void)
 {
 	remove_proc_entry("fs/f2fs", NULL);
 	f2fs_destroy_root_stats();
+	unregister_shrinker(&f2fs_shrinker_info);
 	unregister_filesystem(&f2fs_fs_type);
 	f2fs_exit_crypto();
 	destroy_extent_cache();