What happened in UBIFS during drop cache?

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 would cause the kernel to drop clean caches, dentries and
Inodes from memory, causing the 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 was not freeable, the
User should run ' sync ' first.

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After echo N >/proc/sys/vm/drop_caches, kernel would call function Drop_caches_sysctl_handler, this is the top INTERFAC E to drop caches:

1 intDrop_caches_sysctl_handler (Ctl_table *table,intWrite,2     void__user *buffer, size_t *length, loff_t *PPOs)3 {4     intret;5 6RET =Proc_dointvec_minmax (table, write, buffer, length, ppos);7     if(ret)8         returnret;9     if(write) { Ten         if(Sysctl_drop_caches &1) One iterate_supers (DROP_PAGECACHE_SB, NULL); A         if(Sysctl_drop_caches &2) - Drop_slab (); -     }    the     return 0; -}

FS/DROP_CACHES.C

Drop_slab would call all of the shrinkers to free memory, like Ubifs_shrinker.

In Ubifs_shinker, would free the znodes and TNC tree. Details refer to Ubifs_shrinker in fs/ubifs/shrinker.c.

Author:marty

Date:2016-8-24

The end.

What happened in UBIFS during drop cache?