// SPDX-License-Identifier: GPL-2.0

  /*
   * Implement the manual drop-all-pagecache function
   */
  
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/fs.h>
  #include <linux/writeback.h>
  #include <linux/sysctl.h>
  #include <linux/gfp.h>

  #include "internal.h"

  
  /* A global variable is a bit ugly, but it keeps the code simple */
  int sysctl_drop_caches;

  static void drop_pagecache_sb(struct super_block *sb, void *unused)

  {

  	struct inode *inode, *toput_inode = NULL;

  	spin_lock(&sb->s_inode_list_lock);

  	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {

  		spin_lock(&inode->i_lock);
  		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
  		    (inode->i_mapping->nrpages == 0)) {
  			spin_unlock(&inode->i_lock);

  			continue;

  		}

  		__iget(inode);

  		spin_unlock(&inode->i_lock);

  		spin_unlock(&sb->s_inode_list_lock);

  		invalidate_mapping_pages(inode->i_mapping, 0, -1);

  		iput(toput_inode);
  		toput_inode = inode;

  
  		spin_lock(&sb->s_inode_list_lock);

  	}

  	spin_unlock(&sb->s_inode_list_lock);

  	iput(toput_inode);

  }

  int drop_caches_sysctl_handler(struct ctl_table *table, int write,

  	void __user *buffer, size_t *length, loff_t *ppos)

  {

  	int ret;
  
  	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
  	if (ret)
  		return ret;

  	if (write) {

  		static int stfu;
  
  		if (sysctl_drop_caches & 1) {

  			iterate_supers(drop_pagecache_sb, NULL);

  			count_vm_event(DROP_PAGECACHE);
  		}
  		if (sysctl_drop_caches & 2) {

  			drop_slab();

  			count_vm_event(DROP_SLAB);
  		}
  		if (!stfu) {
  			pr_info("%s (%d): drop_caches: %d
  ",
  				current->comm, task_pid_nr(current),
  				sysctl_drop_caches);
  		}
  		stfu |= sysctl_drop_caches & 4;

  	}
  	return 0;
  }