1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Implement the manual drop-all-pagecache function
4  */
5 
6 #include <linux/pagemap.h>
7 #include <linux/kernel.h>
8 #include <linux/mm.h>
9 #include <linux/fs.h>
10 #include <linux/writeback.h>
11 #include <linux/sysctl.h>
12 #include <linux/gfp.h>
13 #include "internal.h"
14 
15 /* A global variable is a bit ugly, but it keeps the code simple */
16 int sysctl_drop_caches;
17 
drop_pagecache_sb(struct super_block * sb,void * unused)18 static void drop_pagecache_sb(struct super_block *sb, void *unused)
19 {
20 	struct inode *inode, *toput_inode = NULL;
21 
22 	spin_lock(&sb->s_inode_list_lock);
23 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
24 		spin_lock(&inode->i_lock);
25 		/*
26 		 * We must skip inodes in unusual state. We may also skip
27 		 * inodes without pages but we deliberately won't in case
28 		 * we need to reschedule to avoid softlockups.
29 		 */
30 		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
31 		    (mapping_empty(inode->i_mapping) && !need_resched())) {
32 			spin_unlock(&inode->i_lock);
33 			continue;
34 		}
35 		__iget(inode);
36 		spin_unlock(&inode->i_lock);
37 		spin_unlock(&sb->s_inode_list_lock);
38 
39 		invalidate_mapping_pages(inode->i_mapping, 0, -1);
40 		iput(toput_inode);
41 		toput_inode = inode;
42 
43 		cond_resched();
44 		spin_lock(&sb->s_inode_list_lock);
45 	}
46 	spin_unlock(&sb->s_inode_list_lock);
47 	iput(toput_inode);
48 }
49 
drop_caches_sysctl_handler(struct ctl_table * table,int write,void * buffer,size_t * length,loff_t * ppos)50 int drop_caches_sysctl_handler(struct ctl_table *table, int write,
51 		void *buffer, size_t *length, loff_t *ppos)
52 {
53 	int ret;
54 
55 	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
56 	if (ret)
57 		return ret;
58 	if (write) {
59 		static int stfu;
60 
61 		if (sysctl_drop_caches & 1) {
62 			iterate_supers(drop_pagecache_sb, NULL);
63 			count_vm_event(DROP_PAGECACHE);
64 		}
65 		if (sysctl_drop_caches & 2) {
66 			drop_slab();
67 			count_vm_event(DROP_SLAB);
68 		}
69 		if (!stfu) {
70 			pr_info("%s (%d): drop_caches: %d\n",
71 				current->comm, task_pid_nr(current),
72 				sysctl_drop_caches);
73 		}
74 		stfu |= sysctl_drop_caches & 4;
75 	}
76 	return 0;
77 }
78