linux/fs/ubifs/shrinker.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 */

/*
 * This file implements UBIFS shrinker which evicts clean znodes from the TNC
 * tree when Linux VM needs more RAM.
 *
 * We do not implement any LRU lists to find oldest znodes to free because it
 * would add additional overhead to the file system fast paths. So the shrinker
 * just walks the TNC tree when searching for znodes to free.
 *
 * If the root of a TNC sub-tree is clean and old enough, then the children are
 * also clean and old enough. So the shrinker walks the TNC in level order and
 * dumps entire sub-trees.
 *
 * The age of znodes is just the time-stamp when they were last looked at.
 * The current shrinker first tries to evict old znodes, then young ones.
 *
 * Since the shrinker is global, it has to protect against races with FS
 * un-mounts, which is done by the 'ubifs_infos_lock' and 'c->umount_mutex'.
 */

#include "ubifs.h"

/* List of all UBIFS file-system instances */
LIST_HEAD(…);

/*
 * We number each shrinker run and record the number on the ubifs_info structure
 * so that we can easily work out which ubifs_info structures have already been
 * done by the current run.
 */
static unsigned int shrinker_run_no;

/* Protects 'ubifs_infos' list */
DEFINE_SPINLOCK(…);

/* Global clean znode counter (for all mounted UBIFS instances) */
atomic_long_t ubifs_clean_zn_cnt;

/**
 * shrink_tnc - shrink TNC tree.
 * @c: UBIFS file-system description object
 * @nr: number of znodes to free
 * @age: the age of znodes to free
 * @contention: if any contention, this is set to %1
 *
 * This function traverses TNC tree and frees clean znodes. It does not free
 * clean znodes which younger then @age. Returns number of freed znodes.
 */
static int shrink_tnc(struct ubifs_info *c, int nr, int age, int *contention)
{ … }

/**
 * shrink_tnc_trees - shrink UBIFS TNC trees.
 * @nr: number of znodes to free
 * @age: the age of znodes to free
 * @contention: if any contention, this is set to %1
 *
 * This function walks the list of mounted UBIFS file-systems and frees clean
 * znodes which are older than @age, until at least @nr znodes are freed.
 * Returns the number of freed znodes.
 */
static int shrink_tnc_trees(int nr, int age, int *contention)
{ … }

/**
 * kick_a_thread - kick a background thread to start commit.
 *
 * This function kicks a background thread to start background commit. Returns
 * %-1 if a thread was kicked or there is another reason to assume the memory
 * will soon be freed or become freeable. If there are no dirty znodes, returns
 * %0.
 */
static int kick_a_thread(void)
{ … }

unsigned long ubifs_shrink_count(struct shrinker *shrink,
				 struct shrink_control *sc)
{ … }

unsigned long ubifs_shrink_scan(struct shrinker *shrink,
				struct shrink_control *sc)
{ … }