Today I want to know what happend in UBIFS during drop cache.
Drop cache is part of sysctl, you can get the details from Documentation/sysctl/vm.txt as below:
drop_caches
Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not freeable, the
user should run `sync‘ first.
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After echo N > /proc/sys/vm/drop_caches, kernel will call function drop_caches_sysctl_handler, this is the top interface to drop caches:
1 int drop_caches_sysctl_handler(ctl_table *table, int write,
2 void __user *buffer, size_t *length, loff_t *ppos)
3 {
4 int ret;
5
6 ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
7 if (ret)
8 return ret;
9 if (write) {
10 if (sysctl_drop_caches & 1)
11 iterate_supers(drop_pagecache_sb, NULL);
12 if (sysctl_drop_caches & 2)
13 drop_slab();
14 }
15 return 0;
16 }
fs/drop_caches.c
drop_slab will call all the shrinkers to free memory, like ubifs_shrinker.
In ubifs_shinker, will free the znodes and tnc tree. Details please refer to ubifs_shrinker in fs/ubifs/shrinker.c.
Author: Marty
Date: 2016-8-24
The end.