320 lines
9.0 KiB
C
320 lines
9.0 KiB
C
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* This file is part of UBIFS.
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*
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* Copyright (C) 2006-2008 Nokia Corporation.
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*
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* Authors: Artem Bityutskiy (Битюцкий Артём)
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* Adrian Hunter
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*/
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/*
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* This file implements UBIFS shrinker which evicts clean znodes from the TNC
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* tree when Linux VM needs more RAM.
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*
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* We do not implement any LRU lists to find oldest znodes to free because it
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* would add additional overhead to the file system fast paths. So the shrinker
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* just walks the TNC tree when searching for znodes to free.
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*
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* If the root of a TNC sub-tree is clean and old enough, then the children are
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* also clean and old enough. So the shrinker walks the TNC in level order and
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* dumps entire sub-trees.
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*
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* The age of znodes is just the time-stamp when they were last looked at.
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* The current shrinker first tries to evict old znodes, then young ones.
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*
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* Since the shrinker is global, it has to protect against races with FS
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* un-mounts, which is done by the 'ubifs_infos_lock' and 'c->umount_mutex'.
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*/
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#include "ubifs.h"
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/* List of all UBIFS file-system instances */
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LIST_HEAD(ubifs_infos);
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/*
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* We number each shrinker run and record the number on the ubifs_info structure
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* so that we can easily work out which ubifs_info structures have already been
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* done by the current run.
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*/
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static unsigned int shrinker_run_no;
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/* Protects 'ubifs_infos' list */
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DEFINE_SPINLOCK(ubifs_infos_lock);
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/* Global clean znode counter (for all mounted UBIFS instances) */
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atomic_long_t ubifs_clean_zn_cnt;
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/**
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* shrink_tnc - shrink TNC tree.
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* @c: UBIFS file-system description object
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* @nr: number of znodes to free
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* @age: the age of znodes to free
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* @contention: if any contention, this is set to %1
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*
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* This function traverses TNC tree and frees clean znodes. It does not free
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* clean znodes which younger then @age. Returns number of freed znodes.
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*/
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static int shrink_tnc(struct ubifs_info *c, int nr, int age, int *contention)
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{
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int total_freed = 0;
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struct ubifs_znode *znode, *zprev;
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time64_t time = ktime_get_seconds();
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ubifs_assert(c, mutex_is_locked(&c->umount_mutex));
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ubifs_assert(c, mutex_is_locked(&c->tnc_mutex));
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if (!c->zroot.znode || atomic_long_read(&c->clean_zn_cnt) == 0)
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return 0;
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/*
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* Traverse the TNC tree in levelorder manner, so that it is possible
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* to destroy large sub-trees. Indeed, if a znode is old, then all its
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* children are older or of the same age.
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*
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* Note, we are holding 'c->tnc_mutex', so we do not have to lock the
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* 'c->space_lock' when _reading_ 'c->clean_zn_cnt', because it is
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* changed only when the 'c->tnc_mutex' is held.
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*/
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zprev = NULL;
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znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, NULL);
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while (znode && total_freed < nr &&
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atomic_long_read(&c->clean_zn_cnt) > 0) {
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int freed;
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/*
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* If the znode is clean, but it is in the 'c->cnext' list, this
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* means that this znode has just been written to flash as a
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* part of commit and was marked clean. They will be removed
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* from the list at end commit. We cannot change the list,
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* because it is not protected by any mutex (design decision to
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* make commit really independent and parallel to main I/O). So
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* we just skip these znodes.
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*
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* Note, the 'clean_zn_cnt' counters are not updated until
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* after the commit, so the UBIFS shrinker does not report
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* the znodes which are in the 'c->cnext' list as freeable.
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*
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* Also note, if the root of a sub-tree is not in 'c->cnext',
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* then the whole sub-tree is not in 'c->cnext' as well, so it
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* is safe to dump whole sub-tree.
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*/
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if (znode->cnext) {
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/*
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* Very soon these znodes will be removed from the list
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* and become freeable.
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*/
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*contention = 1;
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} else if (!ubifs_zn_dirty(znode) &&
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abs(time - znode->time) >= age) {
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if (znode->parent)
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znode->parent->zbranch[znode->iip].znode = NULL;
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else
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c->zroot.znode = NULL;
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freed = ubifs_destroy_tnc_subtree(c, znode);
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atomic_long_sub(freed, &ubifs_clean_zn_cnt);
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atomic_long_sub(freed, &c->clean_zn_cnt);
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total_freed += freed;
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znode = zprev;
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}
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if (unlikely(!c->zroot.znode))
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break;
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zprev = znode;
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znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, znode);
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cond_resched();
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}
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return total_freed;
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}
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/**
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* shrink_tnc_trees - shrink UBIFS TNC trees.
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* @nr: number of znodes to free
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* @age: the age of znodes to free
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* @contention: if any contention, this is set to %1
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*
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* This function walks the list of mounted UBIFS file-systems and frees clean
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* znodes which are older than @age, until at least @nr znodes are freed.
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* Returns the number of freed znodes.
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*/
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static int shrink_tnc_trees(int nr, int age, int *contention)
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{
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struct ubifs_info *c;
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struct list_head *p;
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unsigned int run_no;
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int freed = 0;
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spin_lock(&ubifs_infos_lock);
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do {
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run_no = ++shrinker_run_no;
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} while (run_no == 0);
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/* Iterate over all mounted UBIFS file-systems and try to shrink them */
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p = ubifs_infos.next;
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while (p != &ubifs_infos) {
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c = list_entry(p, struct ubifs_info, infos_list);
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/*
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* We move the ones we do to the end of the list, so we stop
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* when we see one we have already done.
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*/
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if (c->shrinker_run_no == run_no)
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break;
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if (!mutex_trylock(&c->umount_mutex)) {
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/* Some un-mount is in progress, try next FS */
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*contention = 1;
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p = p->next;
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continue;
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}
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/*
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* We're holding 'c->umount_mutex', so the file-system won't go
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* away.
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*/
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if (!mutex_trylock(&c->tnc_mutex)) {
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mutex_unlock(&c->umount_mutex);
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*contention = 1;
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p = p->next;
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continue;
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}
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spin_unlock(&ubifs_infos_lock);
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/*
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* OK, now we have TNC locked, the file-system cannot go away -
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* it is safe to reap the cache.
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*/
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c->shrinker_run_no = run_no;
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freed += shrink_tnc(c, nr, age, contention);
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mutex_unlock(&c->tnc_mutex);
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spin_lock(&ubifs_infos_lock);
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/* Get the next list element before we move this one */
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p = p->next;
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/*
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* Move this one to the end of the list to provide some
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* fairness.
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*/
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list_move_tail(&c->infos_list, &ubifs_infos);
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mutex_unlock(&c->umount_mutex);
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if (freed >= nr)
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break;
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}
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spin_unlock(&ubifs_infos_lock);
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return freed;
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}
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/**
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* kick_a_thread - kick a background thread to start commit.
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*
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* This function kicks a background thread to start background commit. Returns
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* %-1 if a thread was kicked or there is another reason to assume the memory
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* will soon be freed or become freeable. If there are no dirty znodes, returns
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* %0.
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*/
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static int kick_a_thread(void)
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{
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int i;
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struct ubifs_info *c;
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/*
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* Iterate over all mounted UBIFS file-systems and find out if there is
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* already an ongoing commit operation there. If no, then iterate for
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* the second time and initiate background commit.
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*/
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spin_lock(&ubifs_infos_lock);
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for (i = 0; i < 2; i++) {
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list_for_each_entry(c, &ubifs_infos, infos_list) {
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long dirty_zn_cnt;
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if (!mutex_trylock(&c->umount_mutex)) {
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/*
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* Some un-mount is in progress, it will
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* certainly free memory, so just return.
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*/
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spin_unlock(&ubifs_infos_lock);
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return -1;
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}
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dirty_zn_cnt = atomic_long_read(&c->dirty_zn_cnt);
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if (!dirty_zn_cnt || c->cmt_state == COMMIT_BROKEN ||
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c->ro_mount || c->ro_error) {
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mutex_unlock(&c->umount_mutex);
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continue;
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}
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if (c->cmt_state != COMMIT_RESTING) {
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spin_unlock(&ubifs_infos_lock);
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mutex_unlock(&c->umount_mutex);
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return -1;
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}
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if (i == 1) {
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list_move_tail(&c->infos_list, &ubifs_infos);
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spin_unlock(&ubifs_infos_lock);
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ubifs_request_bg_commit(c);
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mutex_unlock(&c->umount_mutex);
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return -1;
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}
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mutex_unlock(&c->umount_mutex);
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}
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}
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spin_unlock(&ubifs_infos_lock);
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return 0;
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}
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unsigned long ubifs_shrink_count(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt);
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/*
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* Due to the way UBIFS updates the clean znode counter it may
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* temporarily be negative.
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*/
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return clean_zn_cnt >= 0 ? clean_zn_cnt : 1;
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}
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unsigned long ubifs_shrink_scan(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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unsigned long nr = sc->nr_to_scan;
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int contention = 0;
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unsigned long freed;
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long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt);
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if (!clean_zn_cnt) {
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/*
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* No clean znodes, nothing to reap. All we can do in this case
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* is to kick background threads to start commit, which will
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* probably make clean znodes which, in turn, will be freeable.
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* And we return -1 which means will make VM call us again
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* later.
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*/
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dbg_tnc("no clean znodes, kick a thread");
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return kick_a_thread();
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}
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freed = shrink_tnc_trees(nr, OLD_ZNODE_AGE, &contention);
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if (freed >= nr)
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goto out;
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dbg_tnc("not enough old znodes, try to free young ones");
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freed += shrink_tnc_trees(nr - freed, YOUNG_ZNODE_AGE, &contention);
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if (freed >= nr)
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goto out;
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dbg_tnc("not enough young znodes, free all");
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freed += shrink_tnc_trees(nr - freed, 0, &contention);
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if (!freed && contention) {
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dbg_tnc("freed nothing, but contention");
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return SHRINK_STOP;
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}
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out:
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dbg_tnc("%lu znodes were freed, requested %lu", freed, nr);
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return freed;
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}
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