--- /dev/null
+/*
+ * 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);
+ ubifs_assert(atomic_long_read(&c->clean_zn_cnt) >= 0);
+ 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 then @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_del(&c->infos_list);
+ list_add_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_media) {
+ 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_del(&c->infos_list);
+ list_add_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;
+}
+
+int ubifs_shrinker(int nr, gfp_t gfp_mask)
+{
+ int freed, contention = 0;
+ long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt);
+
+ if (nr == 0)
+ return 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 -1;
+ }
+
+out:
+ dbg_tnc("%d znodes were freed, requested %d", freed, nr);
+ return freed;
+}
projects / linux-2.6-microblaze.git / blobdiff