fs/btrfs/async-thread.c

   1 /*
   2  * Copyright (C) 2007 Oracle.  All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public
   6  * License v2 as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public
  14  * License along with this program; if not, write to the
  15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16  * Boston, MA 021110-1307, USA.
  17  */
  18
  19 #include <linux/version.h>
  20 #include <linux/kthread.h>
  21 #include <linux/list.h>
  22 #include <linux/spinlock.h>
  23
  24 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,20)
  25 # include <linux/freezer.h>
  26 #else
  27 # include <linux/sched.h>
  28 #endif
  29
  30 #include "async-thread.h"
  31
  32 /*
  33  * container for the kthread task pointer and the list of pending work
  34  * One of these is allocated per thread.
  35  */
  36 struct btrfs_worker_thread {
  37         /* pool we belong to */
  38         struct btrfs_workers *workers;
  39
  40         /* list of struct btrfs_work that are waiting for service */
  41         struct list_head pending;
  42
  43         /* list of worker threads from struct btrfs_workers */
  44         struct list_head worker_list;
  45
  46         /* kthread */
  47         struct task_struct *task;
  48
  49         /* number of things on the pending list */
  50         atomic_t num_pending;
  51
  52         unsigned long sequence;
  53
  54         /* protects the pending list. */
  55         spinlock_t lock;
  56
  57         /* set to non-zero when this thread is already awake and kicking */
  58         int working;
  59
  60         /* are we currently idle */
  61         int idle;
  62 };
  63
  64 /*
  65  * helper function to move a thread onto the idle list after it
  66  * has finished some requests.
  67  */
  68 static void check_idle_worker(struct btrfs_worker_thread *worker)
  69 {
  70         if (!worker->idle && atomic_read(&worker->num_pending) <
  71             worker->workers->idle_thresh / 2) {
  72                 unsigned long flags;
  73                 spin_lock_irqsave(&worker->workers->lock, flags);
  74                 worker->idle = 1;
  75                 list_move(&worker->worker_list, &worker->workers->idle_list);
  76                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  77         }
  78 }
  79
  80 /*
  81  * helper function to move a thread off the idle list after new
  82  * pending work is added.
  83  */
  84 static void check_busy_worker(struct btrfs_worker_thread *worker)
  85 {
  86         if (worker->idle && atomic_read(&worker->num_pending) >=
  87             worker->workers->idle_thresh) {
  88                 unsigned long flags;
  89                 spin_lock_irqsave(&worker->workers->lock, flags);
  90                 worker->idle = 0;
  91                 list_move_tail(&worker->worker_list,
  92                                &worker->workers->worker_list);
  93                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  94         }
  95 }
  96
  97 /*
  98  * main loop for servicing work items
  99  */
 100 static int worker_loop(void *arg)
 101 {
 102         struct btrfs_worker_thread *worker = arg;
 103         struct list_head *cur;
 104         struct btrfs_work *work;
 105         do {
 106                 spin_lock_irq(&worker->lock);
 107                 while(!list_empty(&worker->pending)) {
 108                         cur = worker->pending.next;
 109                         work = list_entry(cur, struct btrfs_work, list);
 110                         list_del(&work->list);
 111                         clear_bit(0, &work->flags);
 112
 113                         work->worker = worker;
 114                         spin_unlock_irq(&worker->lock);
 115
 116                         work->func(work);
 117
 118                         atomic_dec(&worker->num_pending);
 119                         spin_lock_irq(&worker->lock);
 120                         check_idle_worker(worker);
 121                 }
 122                 worker->working = 0;
 123                 if (freezing(current)) {
 124                         refrigerator();
 125                 } else {
 126                         set_current_state(TASK_INTERRUPTIBLE);
 127                         spin_unlock_irq(&worker->lock);
 128                         schedule();
 129                         __set_current_state(TASK_RUNNING);
 130                 }
 131         } while (!kthread_should_stop());
 132         return 0;
 133 }
 134
 135 /*
 136  * this will wait for all the worker threads to shutdown
 137  */
 138 int btrfs_stop_workers(struct btrfs_workers *workers)
 139 {
 140         struct list_head *cur;
 141         struct btrfs_worker_thread *worker;
 142
 143         list_splice_init(&workers->idle_list, &workers->worker_list);
 144         while(!list_empty(&workers->worker_list)) {
 145                 cur = workers->worker_list.next;
 146                 worker = list_entry(cur, struct btrfs_worker_thread,
 147                                     worker_list);
 148                 kthread_stop(worker->task);
 149                 list_del(&worker->worker_list);
 150                 kfree(worker);
 151         }
 152         return 0;
 153 }
 154
 155 /*
 156  * simple init on struct btrfs_workers
 157  */
 158 void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max)
 159 {
 160         workers->num_workers = 0;
 161         INIT_LIST_HEAD(&workers->worker_list);
 162         INIT_LIST_HEAD(&workers->idle_list);
 163         spin_lock_init(&workers->lock);
 164         workers->max_workers = max;
 165         workers->idle_thresh = 32;
 166         workers->name = name;
 167 }
 168
 169 /*
 170  * starts new worker threads.  This does not enforce the max worker
 171  * count in case you need to temporarily go past it.
 172  */
 173 int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
 174 {
 175         struct btrfs_worker_thread *worker;
 176         int ret = 0;
 177         int i;
 178
 179         for (i = 0; i < num_workers; i++) {
 180                 worker = kzalloc(sizeof(*worker), GFP_NOFS);
 181                 if (!worker) {
 182                         ret = -ENOMEM;
 183                         goto fail;
 184                 }
 185
 186                 INIT_LIST_HEAD(&worker->pending);
 187                 INIT_LIST_HEAD(&worker->worker_list);
 188                 spin_lock_init(&worker->lock);
 189                 atomic_set(&worker->num_pending, 0);
 190                 worker->task = kthread_run(worker_loop, worker,
 191                                            "btrfs-%s-%d", workers->name,
 192                                            workers->num_workers + i);
 193                 worker->workers = workers;
 194                 if (IS_ERR(worker->task)) {
 195                         kfree(worker);
 196                         ret = PTR_ERR(worker->task);
 197                         goto fail;
 198                 }
 199
 200                 spin_lock_irq(&workers->lock);
 201                 list_add_tail(&worker->worker_list, &workers->idle_list);
 202                 worker->idle = 1;
 203                 workers->num_workers++;
 204                 spin_unlock_irq(&workers->lock);
 205         }
 206         return 0;
 207 fail:
 208         btrfs_stop_workers(workers);
 209         return ret;
 210 }
 211
 212 /*
 213  * run through the list and find a worker thread that doesn't have a lot
 214  * to do right now.  This can return null if we aren't yet at the thread
 215  * count limit and all of the threads are busy.
 216  */
 217 static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
 218 {
 219         struct btrfs_worker_thread *worker;
 220         struct list_head *next;
 221         int enforce_min = workers->num_workers < workers->max_workers;
 222
 223         /*
 224          * if we find an idle thread, don't move it to the end of the
 225          * idle list.  This improves the chance that the next submission
 226          * will reuse the same thread, and maybe catch it while it is still
 227          * working
 228          */
 229         if (!list_empty(&workers->idle_list)) {
 230                 next = workers->idle_list.next;
 231                 worker = list_entry(next, struct btrfs_worker_thread,
 232                                     worker_list);
 233                 return worker;
 234         }
 235         if (enforce_min || list_empty(&workers->worker_list))
 236                 return NULL;
 237
 238         /*
 239          * if we pick a busy task, move the task to the end of the list.
 240          * hopefully this will keep things somewhat evenly balanced
 241          */
 242         next = workers->worker_list.next;
 243         worker = list_entry(next, struct btrfs_worker_thread, worker_list);
 244         atomic_inc(&worker->num_pending);
 245         worker->sequence++;
 246         if (worker->sequence % workers->idle_thresh == 0)
 247                 list_move_tail(next, &workers->worker_list);
 248         return worker;
 249 }
 250
 251 static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
 252 {
 253         struct btrfs_worker_thread *worker;
 254         unsigned long flags;
 255
 256 again:
 257         spin_lock_irqsave(&workers->lock, flags);
 258         worker = next_worker(workers);
 259         spin_unlock_irqrestore(&workers->lock, flags);
 260
 261         if (!worker) {
 262                 spin_lock_irqsave(&workers->lock, flags);
 263                 if (workers->num_workers >= workers->max_workers) {
 264                         struct list_head *fallback = NULL;
 265                         /*
 266                          * we have failed to find any workers, just
 267                          * return the force one
 268                          */
 269                         if (!list_empty(&workers->worker_list))
 270                                 fallback = workers->worker_list.next;
 271                         if (!list_empty(&workers->idle_list))
 272                                 fallback = workers->idle_list.next;
 273                         BUG_ON(!fallback);
 274                         worker = list_entry(fallback,
 275                                   struct btrfs_worker_thread, worker_list);
 276                         spin_unlock_irqrestore(&workers->lock, flags);
 277                 } else {
 278                         spin_unlock_irqrestore(&workers->lock, flags);
 279                         /* we're below the limit, start another worker */
 280                         btrfs_start_workers(workers, 1);
 281                         goto again;
 282                 }
 283         }
 284         return worker;
 285 }
 286
 287 /*
 288  * btrfs_requeue_work just puts the work item back on the tail of the list
 289  * it was taken from.  It is intended for use with long running work functions
 290  * that make some progress and want to give the cpu up for others.
 291  */
 292 int btrfs_requeue_work(struct btrfs_work *work)
 293 {
 294         struct btrfs_worker_thread *worker = work->worker;
 295         unsigned long flags;
 296
 297         if (test_and_set_bit(0, &work->flags))
 298                 goto out;
 299
 300         spin_lock_irqsave(&worker->lock, flags);
 301         atomic_inc(&worker->num_pending);
 302         list_add_tail(&work->list, &worker->pending);
 303         check_busy_worker(worker);
 304         spin_unlock_irqrestore(&worker->lock, flags);
 305 out:
 306         return 0;
 307 }
 308
 309 /*
 310  * places a struct btrfs_work into the pending queue of one of the kthreads
 311  */
 312 int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
 313 {
 314         struct btrfs_worker_thread *worker;
 315         unsigned long flags;
 316         int wake = 0;
 317
 318         /* don't requeue something already on a list */
 319         if (test_and_set_bit(0, &work->flags))
 320                 goto out;
 321
 322         worker = find_worker(workers);
 323
 324         spin_lock_irqsave(&worker->lock, flags);
 325         atomic_inc(&worker->num_pending);
 326         check_busy_worker(worker);
 327         list_add_tail(&work->list, &worker->pending);
 328
 329         /*
 330          * avoid calling into wake_up_process if this thread has already
 331          * been kicked
 332          */
 333         if (!worker->working)
 334                 wake = 1;
 335         worker->working = 1;
 336
 337         spin_unlock_irqrestore(&worker->lock, flags);
 338
 339         if (wake)
 340                 wake_up_process(worker->task);
 341 out:
 342         return 0;
 343 }