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 #define WORK_HIGH_PRIO_BIT 3
  29
  30 /*
  31  * container for the kthread task pointer and the list of pending work
  32  * One of these is allocated per thread.
  33  */
  34 struct btrfs_worker_thread {
  35         /* pool we belong to */
  36         struct btrfs_workers *workers;
  37
  38         /* list of struct btrfs_work that are waiting for service */
  39         struct list_head pending;
  40         struct list_head prio_pending;
  41
  42         /* list of worker threads from struct btrfs_workers */
  43         struct list_head worker_list;
  44
  45         /* kthread */
  46         struct task_struct *task;
  47
  48         /* number of things on the pending list */
  49         atomic_t num_pending;
  50
  51         unsigned long sequence;
  52
  53         /* protects the pending list. */
  54         spinlock_t lock;
  55
  56         /* set to non-zero when this thread is already awake and kicking */
  57         int working;
  58
  59         /* are we currently idle */
  60         int idle;
  61 };
  62
  63 /*
  64  * helper function to move a thread onto the idle list after it
  65  * has finished some requests.
  66  */
  67 static void check_idle_worker(struct btrfs_worker_thread *worker)
  68 {
  69         if (!worker->idle && atomic_read(&worker->num_pending) <
  70             worker->workers->idle_thresh / 2) {
  71                 unsigned long flags;
  72                 spin_lock_irqsave(&worker->workers->lock, flags);
  73                 worker->idle = 1;
  74                 list_move(&worker->worker_list, &worker->workers->idle_list);
  75                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  76         }
  77 }
  78
  79 /*
  80  * helper function to move a thread off the idle list after new
  81  * pending work is added.
  82  */
  83 static void check_busy_worker(struct btrfs_worker_thread *worker)
  84 {
  85         if (worker->idle && atomic_read(&worker->num_pending) >=
  86             worker->workers->idle_thresh) {
  87                 unsigned long flags;
  88                 spin_lock_irqsave(&worker->workers->lock, flags);
  89                 worker->idle = 0;
  90                 list_move_tail(&worker->worker_list,
  91                                &worker->workers->worker_list);
  92                 spin_unlock_irqrestore(&worker->workers->lock, flags);
  93         }
  94 }
  95
  96 static noinline int run_ordered_completions(struct btrfs_workers *workers,
  97                                             struct btrfs_work *work)
  98 {
  99         unsigned long flags;
 100
 101         if (!workers->ordered)
 102                 return 0;
 103
 104         set_bit(WORK_DONE_BIT, &work->flags);
 105
 106         spin_lock_irqsave(&workers->lock, flags);
 107
 108         while (1) {
 109                 if (!list_empty(&workers->prio_order_list)) {
 110                         work = list_entry(workers->prio_order_list.next,
 111                                           struct btrfs_work, order_list);
 112                 } else if (!list_empty(&workers->order_list)) {
 113                         work = list_entry(workers->order_list.next,
 114                                           struct btrfs_work, order_list);
 115                 } else {
 116                         break;
 117                 }
 118                 if (!test_bit(WORK_DONE_BIT, &work->flags))
 119                         break;
 120
 121                 /* we are going to call the ordered done function, but
 122                  * we leave the work item on the list as a barrier so
 123                  * that later work items that are done don't have their
 124                  * functions called before this one returns
 125                  */
 126                 if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
 127                         break;
 128
 129                 spin_unlock_irqrestore(&workers->lock, flags);
 130
 131                 work->ordered_func(work);
 132
 133                 /* now take the lock again and call the freeing code */
 134                 spin_lock_irqsave(&workers->lock, flags);
 135                 list_del(&work->order_list);
 136                 work->ordered_free(work);
 137         }
 138
 139         spin_unlock_irqrestore(&workers->lock, flags);
 140         return 0;
 141 }
 142
 143 /*
 144  * main loop for servicing work items
 145  */
 146 static int worker_loop(void *arg)
 147 {
 148         struct btrfs_worker_thread *worker = arg;
 149         struct list_head *cur;
 150         struct btrfs_work *work;
 151         do {
 152                 spin_lock_irq(&worker->lock);
 153 again_locked:
 154                 while (1) {
 155                         if (!list_empty(&worker->prio_pending))
 156                                 cur = worker->prio_pending.next;
 157                         else if (!list_empty(&worker->pending))
 158                                 cur = worker->pending.next;
 159                         else
 160                                 break;
 161
 162                         work = list_entry(cur, struct btrfs_work, list);
 163                         list_del(&work->list);
 164                         clear_bit(WORK_QUEUED_BIT, &work->flags);
 165
 166                         work->worker = worker;
 167                         spin_unlock_irq(&worker->lock);
 168
 169                         work->func(work);
 170
 171                         atomic_dec(&worker->num_pending);
 172                         /*
 173                          * unless this is an ordered work queue,
 174                          * 'work' was probably freed by func above.
 175                          */
 176                         run_ordered_completions(worker->workers, work);
 177
 178                         spin_lock_irq(&worker->lock);
 179                         check_idle_worker(worker);
 180                 }
 181                 if (freezing(current)) {
 182                         worker->working = 0;
 183                         spin_unlock_irq(&worker->lock);
 184                         refrigerator();
 185                 } else {
 186                         spin_unlock_irq(&worker->lock);
 187                         if (!kthread_should_stop()) {
 188                                 cpu_relax();
 189                                 /*
 190                                  * we've dropped the lock, did someone else
 191                                  * jump_in?
 192                                  */
 193                                 smp_mb();
 194                                 if (!list_empty(&worker->pending) ||
 195                                     !list_empty(&worker->prio_pending))
 196                                         continue;
 197
 198                                 /*
 199                                  * this short schedule allows more work to
 200                                  * come in without the queue functions
 201                                  * needing to go through wake_up_process()
 202                                  *
 203                                  * worker->working is still 1, so nobody
 204                                  * is going to try and wake us up
 205                                  */
 206                                 schedule_timeout(1);
 207                                 smp_mb();
 208                                 if (!list_empty(&worker->pending) ||
 209                                     !list_empty(&worker->prio_pending))
 210                                         continue;
 211
 212                                 if (kthread_should_stop())
 213                                         break;
 214
 215                                 /* still no more work?, sleep for real */
 216                                 spin_lock_irq(&worker->lock);
 217                                 set_current_state(TASK_INTERRUPTIBLE);
 218                                 if (!list_empty(&worker->pending) ||
 219                                     !list_empty(&worker->prio_pending))
 220                                         goto again_locked;
 221
 222                                 /*
 223                                  * this makes sure we get a wakeup when someone
 224                                  * adds something new to the queue
 225                                  */
 226                                 worker->working = 0;
 227                                 spin_unlock_irq(&worker->lock);
 228
 229                                 if (!kthread_should_stop())
 230                                         schedule();
 231                         }
 232                         __set_current_state(TASK_RUNNING);
 233                 }
 234         } while (!kthread_should_stop());
 235         return 0;
 236 }
 237
 238 /*
 239  * this will wait for all the worker threads to shutdown
 240  */
 241 int btrfs_stop_workers(struct btrfs_workers *workers)
 242 {
 243         struct list_head *cur;
 244         struct btrfs_worker_thread *worker;
 245
 246         list_splice_init(&workers->idle_list, &workers->worker_list);
 247         while (!list_empty(&workers->worker_list)) {
 248                 cur = workers->worker_list.next;
 249                 worker = list_entry(cur, struct btrfs_worker_thread,
 250                                     worker_list);
 251                 kthread_stop(worker->task);
 252                 list_del(&worker->worker_list);
 253                 kfree(worker);
 254         }
 255         return 0;
 256 }
 257
 258 /*
 259  * simple init on struct btrfs_workers
 260  */
 261 void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max)
 262 {
 263         workers->num_workers = 0;
 264         INIT_LIST_HEAD(&workers->worker_list);
 265         INIT_LIST_HEAD(&workers->idle_list);
 266         INIT_LIST_HEAD(&workers->order_list);
 267         INIT_LIST_HEAD(&workers->prio_order_list);
 268         spin_lock_init(&workers->lock);
 269         workers->max_workers = max;
 270         workers->idle_thresh = 32;
 271         workers->name = name;
 272         workers->ordered = 0;
 273 }
 274
 275 /*
 276  * starts new worker threads.  This does not enforce the max worker
 277  * count in case you need to temporarily go past it.
 278  */
 279 int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
 280 {
 281         struct btrfs_worker_thread *worker;
 282         int ret = 0;
 283         int i;
 284
 285         for (i = 0; i < num_workers; i++) {
 286                 worker = kzalloc(sizeof(*worker), GFP_NOFS);
 287                 if (!worker) {
 288                         ret = -ENOMEM;
 289                         goto fail;
 290                 }
 291
 292                 INIT_LIST_HEAD(&worker->pending);
 293                 INIT_LIST_HEAD(&worker->prio_pending);
 294                 INIT_LIST_HEAD(&worker->worker_list);
 295                 spin_lock_init(&worker->lock);
 296                 atomic_set(&worker->num_pending, 0);
 297                 worker->workers = workers;
 298                 worker->task = kthread_run(worker_loop, worker,
 299                                            "btrfs-%s-%d", workers->name,
 300                                            workers->num_workers + i);
 301                 if (IS_ERR(worker->task)) {
 302                         ret = PTR_ERR(worker->task);
 303                         kfree(worker);
 304                         goto fail;
 305                 }
 306
 307                 spin_lock_irq(&workers->lock);
 308                 list_add_tail(&worker->worker_list, &workers->idle_list);
 309                 worker->idle = 1;
 310                 workers->num_workers++;
 311                 spin_unlock_irq(&workers->lock);
 312         }
 313         return 0;
 314 fail:
 315         btrfs_stop_workers(workers);
 316         return ret;
 317 }
 318
 319 /*
 320  * run through the list and find a worker thread that doesn't have a lot
 321  * to do right now.  This can return null if we aren't yet at the thread
 322  * count limit and all of the threads are busy.
 323  */
 324 static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
 325 {
 326         struct btrfs_worker_thread *worker;
 327         struct list_head *next;
 328         int enforce_min = workers->num_workers < workers->max_workers;
 329
 330         /*
 331          * if we find an idle thread, don't move it to the end of the
 332          * idle list.  This improves the chance that the next submission
 333          * will reuse the same thread, and maybe catch it while it is still
 334          * working
 335          */
 336         if (!list_empty(&workers->idle_list)) {
 337                 next = workers->idle_list.next;
 338                 worker = list_entry(next, struct btrfs_worker_thread,
 339                                     worker_list);
 340                 return worker;
 341         }
 342         if (enforce_min || list_empty(&workers->worker_list))
 343                 return NULL;
 344
 345         /*
 346          * if we pick a busy task, move the task to the end of the list.
 347          * hopefully this will keep things somewhat evenly balanced.
 348          * Do the move in batches based on the sequence number.  This groups
 349          * requests submitted at roughly the same time onto the same worker.
 350          */
 351         next = workers->worker_list.next;
 352         worker = list_entry(next, struct btrfs_worker_thread, worker_list);
 353         atomic_inc(&worker->num_pending);
 354         worker->sequence++;
 355
 356         if (worker->sequence % workers->idle_thresh == 0)
 357                 list_move_tail(next, &workers->worker_list);
 358         return worker;
 359 }
 360
 361 /*
 362  * selects a worker thread to take the next job.  This will either find
 363  * an idle worker, start a new worker up to the max count, or just return
 364  * one of the existing busy workers.
 365  */
 366 static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
 367 {
 368         struct btrfs_worker_thread *worker;
 369         unsigned long flags;
 370
 371 again:
 372         spin_lock_irqsave(&workers->lock, flags);
 373         worker = next_worker(workers);
 374         spin_unlock_irqrestore(&workers->lock, flags);
 375
 376         if (!worker) {
 377                 spin_lock_irqsave(&workers->lock, flags);
 378                 if (workers->num_workers >= workers->max_workers) {
 379                         struct list_head *fallback = NULL;
 380                         /*
 381                          * we have failed to find any workers, just
 382                          * return the force one
 383                          */
 384                         if (!list_empty(&workers->worker_list))
 385                                 fallback = workers->worker_list.next;
 386                         if (!list_empty(&workers->idle_list))
 387                                 fallback = workers->idle_list.next;
 388                         BUG_ON(!fallback);
 389                         worker = list_entry(fallback,
 390                                   struct btrfs_worker_thread, worker_list);
 391                         spin_unlock_irqrestore(&workers->lock, flags);
 392                 } else {
 393                         spin_unlock_irqrestore(&workers->lock, flags);
 394                         /* we're below the limit, start another worker */
 395                         btrfs_start_workers(workers, 1);
 396                         goto again;
 397                 }
 398         }
 399         return worker;
 400 }
 401
 402 /*
 403  * btrfs_requeue_work just puts the work item back on the tail of the list
 404  * it was taken from.  It is intended for use with long running work functions
 405  * that make some progress and want to give the cpu up for others.
 406  */
 407 int btrfs_requeue_work(struct btrfs_work *work)
 408 {
 409         struct btrfs_worker_thread *worker = work->worker;
 410         unsigned long flags;
 411         int wake = 0;
 412
 413         if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 414                 goto out;
 415
 416         spin_lock_irqsave(&worker->lock, flags);
 417         if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
 418                 list_add_tail(&work->list, &worker->prio_pending);
 419         else
 420                 list_add_tail(&work->list, &worker->pending);
 421         atomic_inc(&worker->num_pending);
 422
 423         /* by definition we're busy, take ourselves off the idle
 424          * list
 425          */
 426         if (worker->idle) {
 427                 spin_lock_irqsave(&worker->workers->lock, flags);
 428                 worker->idle = 0;
 429                 list_move_tail(&worker->worker_list,
 430                                &worker->workers->worker_list);
 431                 spin_unlock_irqrestore(&worker->workers->lock, flags);
 432         }
 433         if (!worker->working) {
 434                 wake = 1;
 435                 worker->working = 1;
 436         }
 437
 438         spin_unlock_irqrestore(&worker->lock, flags);
 439         if (wake)
 440                 wake_up_process(worker->task);
 441 out:
 442
 443         return 0;
 444 }
 445
 446 void btrfs_set_work_high_prio(struct btrfs_work *work)
 447 {
 448         set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
 449 }
 450
 451 /*
 452  * places a struct btrfs_work into the pending queue of one of the kthreads
 453  */
 454 int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
 455 {
 456         struct btrfs_worker_thread *worker;
 457         unsigned long flags;
 458         int wake = 0;
 459
 460         /* don't requeue something already on a list */
 461         if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 462                 goto out;
 463
 464         worker = find_worker(workers);
 465         if (workers->ordered) {
 466                 spin_lock_irqsave(&workers->lock, flags);
 467                 if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
 468                         list_add_tail(&work->order_list,
 469                                       &workers->prio_order_list);
 470                 } else {
 471                         list_add_tail(&work->order_list, &workers->order_list);
 472                 }
 473                 spin_unlock_irqrestore(&workers->lock, flags);
 474         } else {
 475                 INIT_LIST_HEAD(&work->order_list);
 476         }
 477
 478         spin_lock_irqsave(&worker->lock, flags);
 479
 480         if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
 481                 list_add_tail(&work->list, &worker->prio_pending);
 482         else
 483                 list_add_tail(&work->list, &worker->pending);
 484         atomic_inc(&worker->num_pending);
 485         check_busy_worker(worker);
 486
 487         /*
 488          * avoid calling into wake_up_process if this thread has already
 489          * been kicked
 490          */
 491         if (!worker->working)
 492                 wake = 1;
 493         worker->working = 1;
 494
 495         spin_unlock_irqrestore(&worker->lock, flags);
 496
 497         if (wake)
 498                 wake_up_process(worker->task);
 499 out:
 500         return 0;
 501 }