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Diffstat (limited to 'fs/ubifs/shrinker.c')
| -rw-r--r-- | fs/ubifs/shrinker.c | 331 |
1 files changed, 331 insertions, 0 deletions
diff --git a/fs/ubifs/shrinker.c b/fs/ubifs/shrinker.c new file mode 100644 index 000000000..9a9fb94a4 --- /dev/null +++ b/fs/ubifs/shrinker.c @@ -0,0 +1,331 @@ +/* + * This file is part of UBIFS. + * + * Copyright (C) 2006-2008 Nokia Corporation. + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published by + * the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + * + * You should have received a copy of the GNU General Public License along with + * this program; if not, write to the Free Software Foundation, Inc., 51 + * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + * + * 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(ubifs_infos); + +/* + * 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(ubifs_infos_lock); + +/* 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) +{ + int total_freed = 0; + struct ubifs_znode *znode, *zprev; + int time = get_seconds(); + + ubifs_assert(mutex_is_locked(&c->umount_mutex)); + ubifs_assert(mutex_is_locked(&c->tnc_mutex)); + + if (!c->zroot.znode || atomic_long_read(&c->clean_zn_cnt) == 0) + return 0; + + /* + * Traverse the TNC tree in levelorder manner, so that it is possible + * to destroy large sub-trees. Indeed, if a znode is old, then all its + * children are older or of the same age. + * + * Note, we are holding 'c->tnc_mutex', so we do not have to lock the + * 'c->space_lock' when _reading_ 'c->clean_zn_cnt', because it is + * changed only when the 'c->tnc_mutex' is held. + */ + zprev = NULL; + znode = ubifs_tnc_levelorder_next(c->zroot.znode, NULL); + while (znode && total_freed < nr && + atomic_long_read(&c->clean_zn_cnt) > 0) { + int freed; + + /* + * If the znode is clean, but it is in the 'c->cnext' list, this + * means that this znode has just been written to flash as a + * part of commit and was marked clean. They will be removed + * from the list at end commit. We cannot change the list, + * because it is not protected by any mutex (design decision to + * make commit really independent and parallel to main I/O). So + * we just skip these znodes. + * + * Note, the 'clean_zn_cnt' counters are not updated until + * after the commit, so the UBIFS shrinker does not report + * the znodes which are in the 'c->cnext' list as freeable. + * + * Also note, if the root of a sub-tree is not in 'c->cnext', + * then the whole sub-tree is not in 'c->cnext' as well, so it + * is safe to dump whole sub-tree. + */ + + if (znode->cnext) { + /* + * Very soon these znodes will be removed from the list + * and become freeable. + */ + *contention = 1; + } else if (!ubifs_zn_dirty(znode) && + abs(time - znode->time) >= age) { + if (znode->parent) + znode->parent->zbranch[znode->iip].znode = NULL; + else + c->zroot.znode = NULL; + + freed = ubifs_destroy_tnc_subtree(znode); + atomic_long_sub(freed, &ubifs_clean_zn_cnt); + atomic_long_sub(freed, &c->clean_zn_cnt); + total_freed += freed; + znode = zprev; + } + + if (unlikely(!c->zroot.znode)) + break; + + zprev = znode; + znode = ubifs_tnc_levelorder_next(c->zroot.znode, znode); + cond_resched(); + } + + return total_freed; +} + +/** + * 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) +{ + struct ubifs_info *c; + struct list_head *p; + unsigned int run_no; + int freed = 0; + + spin_lock(&ubifs_infos_lock); + do { + run_no = ++shrinker_run_no; + } while (run_no == 0); + /* Iterate over all mounted UBIFS file-systems and try to shrink them */ + p = ubifs_infos.next; + while (p != &ubifs_infos) { + c = list_entry(p, struct ubifs_info, infos_list); + /* + * We move the ones we do to the end of the list, so we stop + * when we see one we have already done. + */ + if (c->shrinker_run_no == run_no) + break; + if (!mutex_trylock(&c->umount_mutex)) { + /* Some un-mount is in progress, try next FS */ + *contention = 1; + p = p->next; + continue; + } + /* + * We're holding 'c->umount_mutex', so the file-system won't go + * away. + */ + if (!mutex_trylock(&c->tnc_mutex)) { + mutex_unlock(&c->umount_mutex); + *contention = 1; + p = p->next; + continue; + } + spin_unlock(&ubifs_infos_lock); + /* + * OK, now we have TNC locked, the file-system cannot go away - + * it is safe to reap the cache. + */ + c->shrinker_run_no = run_no; + freed += shrink_tnc(c, nr, age, contention); + mutex_unlock(&c->tnc_mutex); + spin_lock(&ubifs_infos_lock); + /* Get the next list element before we move this one */ + p = p->next; + /* + * Move this one to the end of the list to provide some + * fairness. + */ + list_move_tail(&c->infos_list, &ubifs_infos); + mutex_unlock(&c->umount_mutex); + if (freed >= nr) + break; + } + spin_unlock(&ubifs_infos_lock); + return freed; +} + +/** + * 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) +{ + int i; + struct ubifs_info *c; + + /* + * Iterate over all mounted UBIFS file-systems and find out if there is + * already an ongoing commit operation there. If no, then iterate for + * the second time and initiate background commit. + */ + spin_lock(&ubifs_infos_lock); + for (i = 0; i < 2; i++) { + list_for_each_entry(c, &ubifs_infos, infos_list) { + long dirty_zn_cnt; + + if (!mutex_trylock(&c->umount_mutex)) { + /* + * Some un-mount is in progress, it will + * certainly free memory, so just return. + */ + spin_unlock(&ubifs_infos_lock); + return -1; + } + + dirty_zn_cnt = atomic_long_read(&c->dirty_zn_cnt); + + if (!dirty_zn_cnt || c->cmt_state == COMMIT_BROKEN || + c->ro_mount || c->ro_error) { + mutex_unlock(&c->umount_mutex); + continue; + } + + if (c->cmt_state != COMMIT_RESTING) { + spin_unlock(&ubifs_infos_lock); + mutex_unlock(&c->umount_mutex); + return -1; + } + + if (i == 1) { + list_move_tail(&c->infos_list, &ubifs_infos); + spin_unlock(&ubifs_infos_lock); + + ubifs_request_bg_commit(c); + mutex_unlock(&c->umount_mutex); + return -1; + } + mutex_unlock(&c->umount_mutex); + } + } + spin_unlock(&ubifs_infos_lock); + + return 0; +} + +unsigned long ubifs_shrink_count(struct shrinker *shrink, + struct shrink_control *sc) +{ + long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt); + + /* + * Due to the way UBIFS updates the clean znode counter it may + * temporarily be negative. + */ + return clean_zn_cnt >= 0 ? clean_zn_cnt : 1; +} + +unsigned long ubifs_shrink_scan(struct shrinker *shrink, + struct shrink_control *sc) +{ + unsigned long nr = sc->nr_to_scan; + int contention = 0; + unsigned long freed; + long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt); + + if (!clean_zn_cnt) { + /* + * No clean znodes, nothing to reap. All we can do in this case + * is to kick background threads to start commit, which will + * probably make clean znodes which, in turn, will be freeable. + * And we return -1 which means will make VM call us again + * later. + */ + dbg_tnc("no clean znodes, kick a thread"); + return kick_a_thread(); + } + + freed = shrink_tnc_trees(nr, OLD_ZNODE_AGE, &contention); + if (freed >= nr) + goto out; + + dbg_tnc("not enough old znodes, try to free young ones"); + freed += shrink_tnc_trees(nr - freed, YOUNG_ZNODE_AGE, &contention); + if (freed >= nr) + goto out; + + dbg_tnc("not enough young znodes, free all"); + freed += shrink_tnc_trees(nr - freed, 0, &contention); + + if (!freed && contention) { + dbg_tnc("freed nothing, but contention"); + return SHRINK_STOP; + } + +out: + dbg_tnc("%lu znodes were freed, requested %lu", freed, nr); + return freed; +} |