drop_caches.c

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/*
 * 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(&inode_sb_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(&inode_sb_list_lock);
        invalidate_mapping_pages(inode->i_mapping, 0, -1);
        iput(toput_inode);
        toput_inode = inode;
        spin_lock(&inode_sb_list_lock);
    }
    spin_unlock(&inode_sb_list_lock);
    iput(toput_inode);
}

static void drop_slab(void)
{
    int nr_objects;
    struct shrink_control shrink = {
        .gfp_mask = GFP_KERNEL,
    };

    do {
        nr_objects = shrink_slab(&shrink, 1000, 1000);
    } while (nr_objects > 10);
}

int drop_caches_sysctl_handler(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) {
        if (sysctl_drop_caches & 1)
            iterate_supers(drop_pagecache_sb, NULL);
        if (sysctl_drop_caches & 2)
            drop_slab();
    }
    return 0;
}