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/kthread.h>
  20 #include <linux/list.h>
  21 #include <linux/spinlock.h>
  22 # include <linux/freezer.h>
  23 #include "async-thread.h"
  24
  25 #define WORK_QUEUED_BIT 0
  26 #define WORK_DONE_BIT 1
  27 #define WORK_ORDER_DONE_BIT 2
  28
  29 /*
  30  * container for the kthread task pointer and the list of pending work
  31  * One of these is allocated per thread.
  32  */
  33 struct btrfs_worker_thread {
  34         /* pool we belong to */
  35         struct btrfs_workers *workers;
  36
  37         /* list of struct btrfs_work that are waiting for service */
  38         struct list_head pending;
  39
  40         /* list of worker threads from struct btrfs_workers */
  41         struct list_head worker_list;
  42
  43         /* kthread */
  44         struct task_struct *task;
  45
  46         /* number of things on the pending list */
  47         atomic_t num_pending;
  48
  49         unsigned long sequence;
  50
  51         /* protects the pending list. */
  52         spinlock_t lock;
  53
  54         /* set to non-zero when this thread is already awake and kicking */
  55         int working;
  56
  57         /* are we currently idle */
  58         int idle;
  59 };
  60
  61 /*
  62  * helper function to move a thread onto the idle list after it
  63  * has finished some requests.
  64  */
  65 static void check_idle_worker(struct btrfs_worker_thread *worker)
  66 {
  67         if (!worker->idle && atomic_read(&worker->num_pending) <
  68             worker->workers->idle_thresh / 2) {
  69                 unsigned long flags;
  70                 spin_lock_irqsave(&worker->workers->lock, flags);
  71                 worker->idle = 1;
  72                 list_move(&worker->worker_list, &worker->workers->idle_list);
  73                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  74         }
  75 }
  76
  77 /*
  78  * helper function to move a thread off the idle list after new
  79  * pending work is added.
  80  */
  81 static void check_busy_worker(struct btrfs_worker_thread *worker)
  82 {
  83         if (worker->idle && atomic_read(&worker->num_pending) >=
  84             worker->workers->idle_thresh) {
  85                 unsigned long flags;
  86                 spin_lock_irqsave(&worker->workers->lock, flags);
  87                 worker->idle = 0;
  88                 list_move_tail(&worker->worker_list,
  89                                &worker->workers->worker_list);
  90                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  91         }
  92 }
  93
  94 static noinline int run_ordered_completions(struct btrfs_workers *workers,
  95                                             struct btrfs_work *work)
  96 {
  97         unsigned long flags;
  98
  99         if (!workers->ordered)
 100                 return 0;
 101
 102         set_bit(WORK_DONE_BIT, &work->flags);
 103
 104         spin_lock_irqsave(&workers->lock, flags);
 105
 106         while (!list_empty(&workers->order_list)) {
 107                 work = list_entry(workers->order_list.next,
 108                                   struct btrfs_work, order_list);
 109
 110                 if (!test_bit(WORK_DONE_BIT, &work->flags))
 111                         break;
 112
 113                 /* we are going to call the ordered done function, but
 114                  * we leave the work item on the list as a barrier so
 115                  * that later work items that are done don't have their
 116                  * functions called before this one returns
 117                  */
 118                 if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
 119                         break;
 120
 121                 spin_unlock_irqrestore(&workers->lock, flags);
 122
 123                 work->ordered_func(work);
 124
 125                 /* now take the lock again and call the freeing code */
 126                 spin_lock_irqsave(&workers->lock, flags);
 127                 list_del(&work->order_list);
 128                 work->ordered_free(work);
 129         }
 130
 131         spin_unlock_irqrestore(&workers->lock, flags);
 132         return 0;
 133 }
 134
 135 /*
 136  * main loop for servicing work items
 137  */
 138 static int worker_loop(void *arg)
 139 {
 140         struct btrfs_worker_thread *worker = arg;
 141         struct list_head *cur;
 142         struct btrfs_work *work;
 143         do {
 144                 spin_lock_irq(&worker->lock);
 145                 while (!list_empty(&worker->pending)) {
 146                         cur = worker->pending.next;
 147                         work = list_entry(cur, struct btrfs_work, list);
 148                         list_del(&work->list);
 149                         clear_bit(WORK_QUEUED_BIT, &work->flags);
 150
 151                         work->worker = worker;
 152                         spin_unlock_irq(&worker->lock);
 153
 154                         work->func(work);
 155
 156                         atomic_dec(&worker->num_pending);
 157                         /*
 158                          * unless this is an ordered work queue,
 159                          * 'work' was probably freed by func above.
 160                          */
 161                         run_ordered_completions(worker->workers, work);
 162
 163                         spin_lock_irq(&worker->lock);
 164                         check_idle_worker(worker);
 165
 166                 }
 167                 worker->working = 0;
 168                 if (freezing(current)) {
 169                         refrigerator();
 170                 } else {
 171                         set_current_state(TASK_INTERRUPTIBLE);
 172                         spin_unlock_irq(&worker->lock);
 173                         if (!kthread_should_stop())
 174                                 schedule();
 175                         __set_current_state(TASK_RUNNING);
 176                 }
 177         } while (!kthread_should_stop());
 178         return 0;
 179 }
 180
 181 /*
 182  * this will wait for all the worker threads to shutdown
 183  */
 184 int btrfs_stop_workers(struct btrfs_workers *workers)
 185 {
 186         struct list_head *cur;
 187         struct btrfs_worker_thread *worker;
 188
 189         list_splice_init(&workers->idle_list, &workers->worker_list);
 190         while (!list_empty(&workers->worker_list)) {
 191                 cur = workers->worker_list.next;
 192                 worker = list_entry(cur, struct btrfs_worker_thread,
 193                                     worker_list);
 194                 kthread_stop(worker->task);
 195                 list_del(&worker->worker_list);
 196                 kfree(worker);
 197         }
 198         return 0;
 199 }
 200
 201 /*
 202  * simple init on struct btrfs_workers
 203  */
 204 void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max)
 205 {
 206         workers->num_workers = 0;
 207         INIT_LIST_HEAD(&workers->worker_list);
 208         INIT_LIST_HEAD(&workers->idle_list);
 209         INIT_LIST_HEAD(&workers->order_list);
 210         spin_lock_init(&workers->lock);
 211         workers->max_workers = max;
 212         workers->idle_thresh = 32;
 213         workers->name = name;
 214         workers->ordered = 0;
 215 }
 216
 217 /*
 218  * starts new worker threads.  This does not enforce the max worker
 219  * count in case you need to temporarily go past it.
 220  */
 221 int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
 222 {
 223         struct btrfs_worker_thread *worker;
 224         int ret = 0;
 225         int i;
 226
 227         for (i = 0; i < num_workers; i++) {
 228                 worker = kzalloc(sizeof(*worker), GFP_NOFS);
 229                 if (!worker) {
 230                         ret = -ENOMEM;
 231                         goto fail;
 232                 }
 233
 234                 INIT_LIST_HEAD(&worker->pending);
 235                 INIT_LIST_HEAD(&worker->worker_list);
 236                 spin_lock_init(&worker->lock);
 237                 atomic_set(&worker->num_pending, 0);
 238                 worker->task = kthread_run(worker_loop, worker,
 239                                            "btrfs-%s-%d", workers->name,
 240                                            workers->num_workers + i);
 241                 worker->workers = workers;
 242                 if (IS_ERR(worker->task)) {
 243                         kfree(worker);
 244                         ret = PTR_ERR(worker->task);
 245                         goto fail;
 246                 }
 247
 248                 spin_lock_irq(&workers->lock);
 249                 list_add_tail(&worker->worker_list, &workers->idle_list);
 250                 worker->idle = 1;
 251                 workers->num_workers++;
 252                 spin_unlock_irq(&workers->lock);
 253         }
 254         return 0;
 255 fail:
 256         btrfs_stop_workers(workers);
 257         return ret;
 258 }
 259
 260 /*
 261  * run through the list and find a worker thread that doesn't have a lot
 262  * to do right now.  This can return null if we aren't yet at the thread
 263  * count limit and all of the threads are busy.
 264  */
 265 static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
 266 {
 267         struct btrfs_worker_thread *worker;
 268         struct list_head *next;
 269         int enforce_min = workers->num_workers < workers->max_workers;
 270
 271         /*
 272          * if we find an idle thread, don't move it to the end of the
 273          * idle list.  This improves the chance that the next submission
 274          * will reuse the same thread, and maybe catch it while it is still
 275          * working
 276          */
 277         if (!list_empty(&workers->idle_list)) {
 278                 next = workers->idle_list.next;
 279                 worker = list_entry(next, struct btrfs_worker_thread,
 280                                     worker_list);
 281                 return worker;
 282         }
 283         if (enforce_min || list_empty(&workers->worker_list))
 284                 return NULL;
 285
 286         /*
 287          * if we pick a busy task, move the task to the end of the list.
 288          * hopefully this will keep things somewhat evenly balanced.
 289          * Do the move in batches based on the sequence number.  This groups
 290          * requests submitted at roughly the same time onto the same worker.
 291          */
 292         next = workers->worker_list.next;
 293         worker = list_entry(next, struct btrfs_worker_thread, worker_list);
 294         atomic_inc(&worker->num_pending);
 295         worker->sequence++;
 296
 297         if (worker->sequence % workers->idle_thresh == 0)
 298                 list_move_tail(next, &workers->worker_list);
 299         return worker;
 300 }
 301
 302 /*
 303  * selects a worker thread to take the next job.  This will either find
 304  * an idle worker, start a new worker up to the max count, or just return
 305  * one of the existing busy workers.
 306  */
 307 static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
 308 {
 309         struct btrfs_worker_thread *worker;
 310         unsigned long flags;
 311
 312 again:
 313         spin_lock_irqsave(&workers->lock, flags);
 314         worker = next_worker(workers);
 315         spin_unlock_irqrestore(&workers->lock, flags);
 316
 317         if (!worker) {
 318                 spin_lock_irqsave(&workers->lock, flags);
 319                 if (workers->num_workers >= workers->max_workers) {
 320                         struct list_head *fallback = NULL;
 321                         /*
 322                          * we have failed to find any workers, just
 323                          * return the force one
 324                          */
 325                         if (!list_empty(&workers->worker_list))
 326                                 fallback = workers->worker_list.next;
 327                         if (!list_empty(&workers->idle_list))
 328                                 fallback = workers->idle_list.next;
 329                         BUG_ON(!fallback);
 330                         worker = list_entry(fallback,
 331                                   struct btrfs_worker_thread, worker_list);
 332                         spin_unlock_irqrestore(&workers->lock, flags);
 333                 } else {
 334                         spin_unlock_irqrestore(&workers->lock, flags);
 335                         /* we're below the limit, start another worker */
 336                         btrfs_start_workers(workers, 1);
 337                         goto again;
 338                 }
 339         }
 340         return worker;
 341 }
 342
 343 /*
 344  * btrfs_requeue_work just puts the work item back on the tail of the list
 345  * it was taken from.  It is intended for use with long running work functions
 346  * that make some progress and want to give the cpu up for others.
 347  */
 348 int btrfs_requeue_work(struct btrfs_work *work)
 349 {
 350         struct btrfs_worker_thread *worker = work->worker;
 351         unsigned long flags;
 352
 353         if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 354                 goto out;
 355
 356         spin_lock_irqsave(&worker->lock, flags);
 357         atomic_inc(&worker->num_pending);
 358         list_add_tail(&work->list, &worker->pending);
 359
 360         /* by definition we're busy, take ourselves off the idle
 361          * list
 362          */
 363         if (worker->idle) {
 364                 spin_lock_irqsave(&worker->workers->lock, flags);
 365                 worker->idle = 0;
 366                 list_move_tail(&worker->worker_list,
 367                                &worker->workers->worker_list);
 368                 spin_unlock_irqrestore(&worker->workers->lock, flags);
 369         }
 370
 371         spin_unlock_irqrestore(&worker->lock, flags);
 372
 373 out:
 374         return 0;
 375 }
 376
 377 /*
 378  * places a struct btrfs_work into the pending queue of one of the kthreads
 379  */
 380 int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
 381 {
 382         struct btrfs_worker_thread *worker;
 383         unsigned long flags;
 384         int wake = 0;
 385
 386         /* don't requeue something already on a list */
 387         if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 388                 goto out;
 389
 390         worker = find_worker(workers);
 391         if (workers->ordered) {
 392                 spin_lock_irqsave(&workers->lock, flags);
 393                 list_add_tail(&work->order_list, &workers->order_list);
 394                 spin_unlock_irqrestore(&workers->lock, flags);
 395         } else {
 396                 INIT_LIST_HEAD(&work->order_list);
 397         }
 398
 399         spin_lock_irqsave(&worker->lock, flags);
 400         atomic_inc(&worker->num_pending);
 401         check_busy_worker(worker);
 402         list_add_tail(&work->list, &worker->pending);
 403
 404         /*
 405          * avoid calling into wake_up_process if this thread has already
 406          * been kicked
 407          */
 408         if (!worker->working)
 409                 wake = 1;
 410         worker->working = 1;
 411
 412         spin_unlock_irqrestore(&worker->lock, flags);
 413
 414         if (wake)
 415                 wake_up_process(worker->task);
 416 out:
 417         return 0;
 418 }