1.添加inode到inode cache链表

当inode的引用计数器i_count为0后，会调用iput_final去释放

static void iput_final(struct inode *inode)
{struct super_block *sb = inode->i_sb;const struct super_operations *op = inode->i_sb->s_op;unsigned long state;int drop;WARN_ON(inode->i_state & I_NEW);if (op->drop_inode)drop = op->drop_inode(inode);elsedrop = generic_drop_inode(inode);//引用计数为0之后，将inode放到lru中，等待回收if (!drop &&!(inode->i_state & I_DONTCACHE) &&(sb->s_flags & SB_ACTIVE)) {inode_add_lru(inode);spin_unlock(&inode->i_lock);return;}//对于已经被文件系统除名的文件，即i_nlink = 0, 不必再保留inode，直接释放掉WRITE_ONCE(inode->i_state, state | I_FREEING);if (!list_empty(&inode->i_lru))inode_lru_list_del(inode);spin_unlock(&inode->i_lock);evict(inode);
}

2.从inode cache中删除inode

在系统需要回收内存时，就会对这个链表下手，回收最近最少使用的inode。

long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
{LIST_HEAD(freeable);long freed;//遍历超级块的s_inode_lru链表，按照回收控制结构sc指定的回收数量，//将可回收的inode隔离到freeable链表中集中回收freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,inode_lru_isolate, &freeable);//将隔离出来的inode进行回收，这样隔离后可以避免锁竞争dispose_list(&freeable);return freed;
}

static void dispose_list(struct list_head *head)
{while (!list_empty(head)) {struct inode *inode;inode = list_first_entry(head, struct inode, i_lru);//将inode从超级块的s_inode_lru链表摘除list_del_init(&inode->i_lru);//回收inodeevict(inode);cond_resched();}
}static void evict(struct inode *inode)
{const struct super_operations *op = inode->i_sb->s_op;BUG_ON(!(inode->i_state & I_FREEING));BUG_ON(!list_empty(&inode->i_lru));//从bdi_writeback的b_io链表摘除if (!list_empty(&inode->i_io_list))inode_io_list_del(inode);//将inode从超级块的s_inodes链表摘除inode_sb_list_del(inode);//等待该inode回写完毕inode_wait_for_writeback(inode);//调用对应文件系统的evict_inode方法，回写pagecacheif (op->evict_inode) {op->evict_inode(inode);} else {truncate_inode_pages_final(&inode->i_data);clear_inode(inode);}//如果是块设备inodeif (S_ISBLK(inode->i_mode) && inode->i_bdev)bd_forget(inode);//如果是字符型设备if (S_ISCHR(inode->i_mode) && inode->i_cdev)cd_forget(inode);//从全局inode哈希表中摘除remove_inode_hash(inode);...//回收inodedestroy_inode(inode);
}

处理完这些引用后，就可以调用destroy_inode回收到slab缓存，对于ext4，调用的是ext4_destroy_inode

static void destroy_inode(struct inode *inode)
{BUG_ON(!list_empty(&inode->i_lru));__destroy_inode(inode);//调用对应文件系统的destroy_inode方法，将inode回收到slab缓存//对于ext4，调用的是ext4_destroy_inodeif (inode->i_sb->s_op->destroy_inode)inode->i_sb->s_op->destroy_inode(inode);elsecall_rcu(&inode->i_rcu, i_callback);
}static void ext4_destroy_inode(struct inode *inode)
{	if (!list_empty(&(EXT4_I(inode)->i_orphan))) {...}//调用ext4_i_callback将inode释放会slab缓存call_rcu(&inode->i_rcu, ext4_i_callback);
}static void ext4_i_callback(struct rcu_head *head)
{struct inode *inode = container_of(head, struct inode, i_rcu);//释放回slab缓存kmem_cache_free(ext4_inode_cachep, EXT4_I(inode));
}

3.记忆

• 等待回收：iput_final会把i_count为0的inode放入superblock的LRU链表s_inode_lru【这个链表也称为inode cache】中(inode_lru_list_add函数)
• 正式回收：回收链表s_inode_lru中的节点，大致调用栈：evict->destroy_inode -> ext4_destroy_inode -> ext4_i_callback(释放slab缓存)