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-rw-r--r--fs/btrfs/async-thread.c357
1 files changed, 357 insertions, 0 deletions
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
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+++ b/fs/btrfs/async-thread.c
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+/*
+ * Copyright (C) 2007 Oracle. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 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., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/version.h>
+#include <linux/kthread.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+# include <linux/freezer.h>
+#include "async-thread.h"
+
+/*
+ * container for the kthread task pointer and the list of pending work
+ * One of these is allocated per thread.
+ */
+struct btrfs_worker_thread {
+ /* pool we belong to */
+ struct btrfs_workers *workers;
+
+ /* list of struct btrfs_work that are waiting for service */
+ struct list_head pending;
+
+ /* list of worker threads from struct btrfs_workers */
+ struct list_head worker_list;
+
+ /* kthread */
+ struct task_struct *task;
+
+ /* number of things on the pending list */
+ atomic_t num_pending;
+
+ unsigned long sequence;
+
+ /* protects the pending list. */
+ spinlock_t lock;
+
+ /* set to non-zero when this thread is already awake and kicking */
+ int working;
+
+ /* are we currently idle */
+ int idle;
+};
+
+/*
+ * helper function to move a thread onto the idle list after it
+ * has finished some requests.
+ */
+static void check_idle_worker(struct btrfs_worker_thread *worker)
+{
+ if (!worker->idle && atomic_read(&worker->num_pending) <
+ worker->workers->idle_thresh / 2) {
+ unsigned long flags;
+ spin_lock_irqsave(&worker->workers->lock, flags);
+ worker->idle = 1;
+ list_move(&worker->worker_list, &worker->workers->idle_list);
+ spin_unlock_irqrestore(&worker->workers->lock, flags);
+ }
+}
+
+/*
+ * helper function to move a thread off the idle list after new
+ * pending work is added.
+ */
+static void check_busy_worker(struct btrfs_worker_thread *worker)
+{
+ if (worker->idle && atomic_read(&worker->num_pending) >=
+ worker->workers->idle_thresh) {
+ unsigned long flags;
+ spin_lock_irqsave(&worker->workers->lock, flags);
+ worker->idle = 0;
+ list_move_tail(&worker->worker_list,
+ &worker->workers->worker_list);
+ spin_unlock_irqrestore(&worker->workers->lock, flags);
+ }
+}
+
+/*
+ * main loop for servicing work items
+ */
+static int worker_loop(void *arg)
+{
+ struct btrfs_worker_thread *worker = arg;
+ struct list_head *cur;
+ struct btrfs_work *work;
+ do {
+ spin_lock_irq(&worker->lock);
+ while(!list_empty(&worker->pending)) {
+ cur = worker->pending.next;
+ work = list_entry(cur, struct btrfs_work, list);
+ list_del(&work->list);
+ clear_bit(0, &work->flags);
+
+ work->worker = worker;
+ spin_unlock_irq(&worker->lock);
+
+ work->func(work);
+
+ atomic_dec(&worker->num_pending);
+ spin_lock_irq(&worker->lock);
+ check_idle_worker(worker);
+ }
+ worker->working = 0;
+ if (freezing(current)) {
+ refrigerator();
+ } else {
+ set_current_state(TASK_INTERRUPTIBLE);
+ spin_unlock_irq(&worker->lock);
+ schedule();
+ __set_current_state(TASK_RUNNING);
+ }
+ } while (!kthread_should_stop());
+ return 0;
+}
+
+/*
+ * this will wait for all the worker threads to shutdown
+ */
+int btrfs_stop_workers(struct btrfs_workers *workers)
+{
+ struct list_head *cur;
+ struct btrfs_worker_thread *worker;
+
+ list_splice_init(&workers->idle_list, &workers->worker_list);
+ while(!list_empty(&workers->worker_list)) {
+ cur = workers->worker_list.next;
+ worker = list_entry(cur, struct btrfs_worker_thread,
+ worker_list);
+ kthread_stop(worker->task);
+ list_del(&worker->worker_list);
+ kfree(worker);
+ }
+ return 0;
+}
+
+/*
+ * simple init on struct btrfs_workers
+ */
+void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max)
+{
+ workers->num_workers = 0;
+ INIT_LIST_HEAD(&workers->worker_list);
+ INIT_LIST_HEAD(&workers->idle_list);
+ spin_lock_init(&workers->lock);
+ workers->max_workers = max;
+ workers->idle_thresh = 32;
+ workers->name = name;
+}
+
+/*
+ * starts new worker threads. This does not enforce the max worker
+ * count in case you need to temporarily go past it.
+ */
+int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
+{
+ struct btrfs_worker_thread *worker;
+ int ret = 0;
+ int i;
+
+ for (i = 0; i < num_workers; i++) {
+ worker = kzalloc(sizeof(*worker), GFP_NOFS);
+ if (!worker) {
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ INIT_LIST_HEAD(&worker->pending);
+ INIT_LIST_HEAD(&worker->worker_list);
+ spin_lock_init(&worker->lock);
+ atomic_set(&worker->num_pending, 0);
+ worker->task = kthread_run(worker_loop, worker,
+ "btrfs-%s-%d", workers->name,
+ workers->num_workers + i);
+ worker->workers = workers;
+ if (IS_ERR(worker->task)) {
+ kfree(worker);
+ ret = PTR_ERR(worker->task);
+ goto fail;
+ }
+
+ spin_lock_irq(&workers->lock);
+ list_add_tail(&worker->worker_list, &workers->idle_list);
+ worker->idle = 1;
+ workers->num_workers++;
+ spin_unlock_irq(&workers->lock);
+ }
+ return 0;
+fail:
+ btrfs_stop_workers(workers);
+ return ret;
+}
+
+/*
+ * run through the list and find a worker thread that doesn't have a lot
+ * to do right now. This can return null if we aren't yet at the thread
+ * count limit and all of the threads are busy.
+ */
+static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
+{
+ struct btrfs_worker_thread *worker;
+ struct list_head *next;
+ int enforce_min = workers->num_workers < workers->max_workers;
+
+ /*
+ * if we find an idle thread, don't move it to the end of the
+ * idle list. This improves the chance that the next submission
+ * will reuse the same thread, and maybe catch it while it is still
+ * working
+ */
+ if (!list_empty(&workers->idle_list)) {
+ next = workers->idle_list.next;
+ worker = list_entry(next, struct btrfs_worker_thread,
+ worker_list);
+ return worker;
+ }
+ if (enforce_min || list_empty(&workers->worker_list))
+ return NULL;
+
+ /*
+ * if we pick a busy task, move the task to the end of the list.
+ * hopefully this will keep things somewhat evenly balanced.
+ * Do the move in batches based on the sequence number. This groups
+ * requests submitted at roughly the same time onto the same worker.
+ */
+ next = workers->worker_list.next;
+ worker = list_entry(next, struct btrfs_worker_thread, worker_list);
+ atomic_inc(&worker->num_pending);
+ worker->sequence++;
+
+ if (worker->sequence % workers->idle_thresh == 0)
+ list_move_tail(next, &workers->worker_list);
+ return worker;
+}
+
+/*
+ * selects a worker thread to take the next job. This will either find
+ * an idle worker, start a new worker up to the max count, or just return
+ * one of the existing busy workers.
+ */
+static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
+{
+ struct btrfs_worker_thread *worker;
+ unsigned long flags;
+
+again:
+ spin_lock_irqsave(&workers->lock, flags);
+ worker = next_worker(workers);
+ spin_unlock_irqrestore(&workers->lock, flags);
+
+ if (!worker) {
+ spin_lock_irqsave(&workers->lock, flags);
+ if (workers->num_workers >= workers->max_workers) {
+ struct list_head *fallback = NULL;
+ /*
+ * we have failed to find any workers, just
+ * return the force one
+ */
+ if (!list_empty(&workers->worker_list))
+ fallback = workers->worker_list.next;
+ if (!list_empty(&workers->idle_list))
+ fallback = workers->idle_list.next;
+ BUG_ON(!fallback);
+ worker = list_entry(fallback,
+ struct btrfs_worker_thread, worker_list);
+ spin_unlock_irqrestore(&workers->lock, flags);
+ } else {
+ spin_unlock_irqrestore(&workers->lock, flags);
+ /* we're below the limit, start another worker */
+ btrfs_start_workers(workers, 1);
+ goto again;
+ }
+ }
+ return worker;
+}
+
+/*
+ * btrfs_requeue_work just puts the work item back on the tail of the list
+ * it was taken from. It is intended for use with long running work functions
+ * that make some progress and want to give the cpu up for others.
+ */
+int btrfs_requeue_work(struct btrfs_work *work)
+{
+ struct btrfs_worker_thread *worker = work->worker;
+ unsigned long flags;
+
+ if (test_and_set_bit(0, &work->flags))
+ goto out;
+
+ spin_lock_irqsave(&worker->lock, flags);
+ atomic_inc(&worker->num_pending);
+ list_add_tail(&work->list, &worker->pending);
+
+ /* by definition we're busy, take ourselves off the idle
+ * list
+ */
+ if (worker->idle) {
+ spin_lock_irqsave(&worker->workers->lock, flags);
+ worker->idle = 0;
+ list_move_tail(&worker->worker_list,
+ &worker->workers->worker_list);
+ spin_unlock_irqrestore(&worker->workers->lock, flags);
+ }
+
+ spin_unlock_irqrestore(&worker->lock, flags);
+
+out:
+ return 0;
+}
+
+/*
+ * places a struct btrfs_work into the pending queue of one of the kthreads
+ */
+int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
+{
+ struct btrfs_worker_thread *worker;
+ unsigned long flags;
+ int wake = 0;
+
+ /* don't requeue something already on a list */
+ if (test_and_set_bit(0, &work->flags))
+ goto out;
+
+ worker = find_worker(workers);
+
+ spin_lock_irqsave(&worker->lock, flags);
+ atomic_inc(&worker->num_pending);
+ check_busy_worker(worker);
+ list_add_tail(&work->list, &worker->pending);
+
+ /*
+ * avoid calling into wake_up_process if this thread has already
+ * been kicked
+ */
+ if (!worker->working)
+ wake = 1;
+ worker->working = 1;
+
+ spin_unlock_irqrestore(&worker->lock, flags);
+
+ if (wake)
+ wake_up_process(worker->task);
+out:
+ return 0;
+}