drivers/md/dm-kcopyd.c

   1 /*
   2  * Copyright (C) 2002 Sistina Software (UK) Limited.
   3  * Copyright (C) 2006 Red Hat GmbH
   4  *
   5  * This file is released under the GPL.
   6  *
   7  * Kcopyd provides a simple interface for copying an area of one
   8  * block-device to one or more other block-devices, with an asynchronous
   9  * completion notification.
  10  */
  11
  12 #include <linux/types.h>
  13 #include <linux/atomic.h>
  14 #include <linux/blkdev.h>
  15 #include <linux/fs.h>
  16 #include <linux/init.h>
  17 #include <linux/list.h>
  18 #include <linux/mempool.h>
  19 #include <linux/module.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/slab.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/workqueue.h>
  24 #include <linux/mutex.h>
  25 #include <linux/device-mapper.h>
  26 #include <linux/dm-kcopyd.h>
  27
  28 #include "dm.h"
  29
  30 #define SUB_JOB_SIZE    128
  31 #define SPLIT_COUNT     8
  32 #define MIN_JOBS        8
  33 #define RESERVE_PAGES   (DIV_ROUND_UP(SUB_JOB_SIZE << SECTOR_SHIFT, PAGE_SIZE))
  34
  35 /*-----------------------------------------------------------------
  36  * Each kcopyd client has its own little pool of preallocated
  37  * pages for kcopyd io.
  38  *---------------------------------------------------------------*/
  39 struct dm_kcopyd_client {
  40         struct page_list *pages;
  41         unsigned nr_reserved_pages;
  42         unsigned nr_free_pages;
  43
  44         struct dm_io_client *io_client;
  45
  46         wait_queue_head_t destroyq;
  47         atomic_t nr_jobs;
  48
  49         mempool_t *job_pool;
  50
  51         struct workqueue_struct *kcopyd_wq;
  52         struct work_struct kcopyd_work;
  53
  54 /*
  55  * We maintain three lists of jobs:
  56  *
  57  * i)   jobs waiting for pages
  58  * ii)  jobs that have pages, and are waiting for the io to be issued.
  59  * iii) jobs that have completed.
  60  *
  61  * All three of these are protected by job_lock.
  62  */
  63         spinlock_t job_lock;
  64         struct list_head complete_jobs;
  65         struct list_head io_jobs;
  66         struct list_head pages_jobs;
  67 };
  68
  69 static struct page_list zero_page_list;
  70
  71 static void wake(struct dm_kcopyd_client *kc)
  72 {
  73         queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
  74 }
  75
  76 /*
  77  * Obtain one page for the use of kcopyd.
  78  */
  79 static struct page_list *alloc_pl(gfp_t gfp)
  80 {
  81         struct page_list *pl;
  82
  83         pl = kmalloc(sizeof(*pl), gfp);
  84         if (!pl)
  85                 return NULL;
  86
  87         pl->page = alloc_page(gfp);
  88         if (!pl->page) {
  89                 kfree(pl);
  90                 return NULL;
  91         }
  92
  93         return pl;
  94 }
  95
  96 static void free_pl(struct page_list *pl)
  97 {
  98         __free_page(pl->page);
  99         kfree(pl);
 100 }
 101
 102 /*
 103  * Add the provided pages to a client's free page list, releasing
 104  * back to the system any beyond the reserved_pages limit.
 105  */
 106 static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
 107 {
 108         struct page_list *next;
 109
 110         do {
 111                 next = pl->next;
 112
 113                 if (kc->nr_free_pages >= kc->nr_reserved_pages)
 114                         free_pl(pl);
 115                 else {
 116                         pl->next = kc->pages;
 117                         kc->pages = pl;
 118                         kc->nr_free_pages++;
 119                 }
 120
 121                 pl = next;
 122         } while (pl);
 123 }
 124
 125 static int kcopyd_get_pages(struct dm_kcopyd_client *kc,
 126                             unsigned int nr, struct page_list **pages)
 127 {
 128         struct page_list *pl;
 129
 130         *pages = NULL;
 131
 132         do {
 133                 pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY);
 134                 if (unlikely(!pl)) {
 135                         /* Use reserved pages */
 136                         pl = kc->pages;
 137                         if (unlikely(!pl))
 138                                 goto out_of_memory;
 139                         kc->pages = pl->next;
 140                         kc->nr_free_pages--;
 141                 }
 142                 pl->next = *pages;
 143                 *pages = pl;
 144         } while (--nr);
 145
 146         return 0;
 147
 148 out_of_memory:
 149         if (*pages)
 150                 kcopyd_put_pages(kc, *pages);
 151         return -ENOMEM;
 152 }
 153
 154 /*
 155  * These three functions resize the page pool.
 156  */
 157 static void drop_pages(struct page_list *pl)
 158 {
 159         struct page_list *next;
 160
 161         while (pl) {
 162                 next = pl->next;
 163                 free_pl(pl);
 164                 pl = next;
 165         }
 166 }
 167
 168 /*
 169  * Allocate and reserve nr_pages for the use of a specific client.
 170  */
 171 static int client_reserve_pages(struct dm_kcopyd_client *kc, unsigned nr_pages)
 172 {
 173         unsigned i;
 174         struct page_list *pl = NULL, *next;
 175
 176         for (i = 0; i < nr_pages; i++) {
 177                 next = alloc_pl(GFP_KERNEL);
 178                 if (!next) {
 179                         if (pl)
 180                                 drop_pages(pl);
 181                         return -ENOMEM;
 182                 }
 183                 next->next = pl;
 184                 pl = next;
 185         }
 186
 187         kc->nr_reserved_pages += nr_pages;
 188         kcopyd_put_pages(kc, pl);
 189
 190         return 0;
 191 }
 192
 193 static void client_free_pages(struct dm_kcopyd_client *kc)
 194 {
 195         BUG_ON(kc->nr_free_pages != kc->nr_reserved_pages);
 196         drop_pages(kc->pages);
 197         kc->pages = NULL;
 198         kc->nr_free_pages = kc->nr_reserved_pages = 0;
 199 }
 200
 201 /*-----------------------------------------------------------------
 202  * kcopyd_jobs need to be allocated by the *clients* of kcopyd,
 203  * for this reason we use a mempool to prevent the client from
 204  * ever having to do io (which could cause a deadlock).
 205  *---------------------------------------------------------------*/
 206 struct kcopyd_job {
 207         struct dm_kcopyd_client *kc;
 208         struct list_head list;
 209         unsigned long flags;
 210
 211         /*
 212          * Error state of the job.
 213          */
 214         int read_err;
 215         unsigned long write_err;
 216
 217         /*
 218          * Either READ or WRITE
 219          */
 220         int rw;
 221         struct dm_io_region source;
 222
 223         /*
 224          * The destinations for the transfer.
 225          */
 226         unsigned int num_dests;
 227         struct dm_io_region dests[DM_KCOPYD_MAX_REGIONS];
 228
 229         struct page_list *pages;
 230
 231         /*
 232          * Set this to ensure you are notified when the job has
 233          * completed.  'context' is for callback to use.
 234          */
 235         dm_kcopyd_notify_fn fn;
 236         void *context;
 237
 238         /*
 239          * These fields are only used if the job has been split
 240          * into more manageable parts.
 241          */
 242         struct mutex lock;
 243         atomic_t sub_jobs;
 244         sector_t progress;
 245
 246         struct kcopyd_job *master_job;
 247 };
 248
 249 static struct kmem_cache *_job_cache;
 250
 251 int __init dm_kcopyd_init(void)
 252 {
 253         _job_cache = kmem_cache_create("kcopyd_job",
 254                                 sizeof(struct kcopyd_job) * (SPLIT_COUNT + 1),
 255                                 __alignof__(struct kcopyd_job), 0, NULL);
 256         if (!_job_cache)
 257                 return -ENOMEM;
 258
 259         zero_page_list.next = &zero_page_list;
 260         zero_page_list.page = ZERO_PAGE(0);
 261
 262         return 0;
 263 }
 264
 265 void dm_kcopyd_exit(void)
 266 {
 267         kmem_cache_destroy(_job_cache);
 268         _job_cache = NULL;
 269 }
 270
 271 /*
 272  * Functions to push and pop a job onto the head of a given job
 273  * list.
 274  */
 275 static struct kcopyd_job *pop(struct list_head *jobs,
 276                               struct dm_kcopyd_client *kc)
 277 {
 278         struct kcopyd_job *job = NULL;
 279         unsigned long flags;
 280
 281         spin_lock_irqsave(&kc->job_lock, flags);
 282
 283         if (!list_empty(jobs)) {
 284                 job = list_entry(jobs->next, struct kcopyd_job, list);
 285                 list_del(&job->list);
 286         }
 287         spin_unlock_irqrestore(&kc->job_lock, flags);
 288
 289         return job;
 290 }
 291
 292 static void push(struct list_head *jobs, struct kcopyd_job *job)
 293 {
 294         unsigned long flags;
 295         struct dm_kcopyd_client *kc = job->kc;
 296
 297         spin_lock_irqsave(&kc->job_lock, flags);
 298         list_add_tail(&job->list, jobs);
 299         spin_unlock_irqrestore(&kc->job_lock, flags);
 300 }
 301
 302
 303 static void push_head(struct list_head *jobs, struct kcopyd_job *job)
 304 {
 305         unsigned long flags;
 306         struct dm_kcopyd_client *kc = job->kc;
 307
 308         spin_lock_irqsave(&kc->job_lock, flags);
 309         list_add(&job->list, jobs);
 310         spin_unlock_irqrestore(&kc->job_lock, flags);
 311 }
 312
 313 /*
 314  * These three functions process 1 item from the corresponding
 315  * job list.
 316  *
 317  * They return:
 318  * < 0: error
 319  *   0: success
 320  * > 0: can't process yet.
 321  */
 322 static int run_complete_job(struct kcopyd_job *job)
 323 {
 324         void *context = job->context;
 325         int read_err = job->read_err;
 326         unsigned long write_err = job->write_err;
 327         dm_kcopyd_notify_fn fn = job->fn;
 328         struct dm_kcopyd_client *kc = job->kc;
 329
 330         if (job->pages && job->pages != &zero_page_list)
 331                 kcopyd_put_pages(kc, job->pages);
 332         /*
 333          * If this is the master job, the sub jobs have already
 334          * completed so we can free everything.
 335          */
 336         if (job->master_job == job)
 337                 mempool_free(job, kc->job_pool);
 338         fn(read_err, write_err, context);
 339
 340         if (atomic_dec_and_test(&kc->nr_jobs))
 341                 wake_up(&kc->destroyq);
 342
 343         return 0;
 344 }
 345
 346 static void complete_io(unsigned long error, void *context)
 347 {
 348         struct kcopyd_job *job = (struct kcopyd_job *) context;
 349         struct dm_kcopyd_client *kc = job->kc;
 350
 351         if (error) {
 352                 if (job->rw & WRITE)
 353                         job->write_err |= error;
 354                 else
 355                         job->read_err = 1;
 356
 357                 if (!test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags)) {
 358                         push(&kc->complete_jobs, job);
 359                         wake(kc);
 360                         return;
 361                 }
 362         }
 363
 364         if (job->rw & WRITE)
 365                 push(&kc->complete_jobs, job);
 366
 367         else {
 368                 job->rw = WRITE;
 369                 push(&kc->io_jobs, job);
 370         }
 371
 372         wake(kc);
 373 }
 374
 375 /*
 376  * Request io on as many buffer heads as we can currently get for
 377  * a particular job.
 378  */
 379 static int run_io_job(struct kcopyd_job *job)
 380 {
 381         int r;
 382         struct dm_io_request io_req = {
 383                 .bi_rw = job->rw,
 384                 .mem.type = DM_IO_PAGE_LIST,
 385                 .mem.ptr.pl = job->pages,
 386                 .mem.offset = 0,
 387                 .notify.fn = complete_io,
 388                 .notify.context = job,
 389                 .client = job->kc->io_client,
 390         };
 391
 392         if (job->rw == READ)
 393                 r = dm_io(&io_req, 1, &job->source, NULL);
 394         else
 395                 r = dm_io(&io_req, job->num_dests, job->dests, NULL);
 396
 397         return r;
 398 }
 399
 400 static int run_pages_job(struct kcopyd_job *job)
 401 {
 402         int r;
 403         unsigned nr_pages = dm_div_up(job->dests[0].count, PAGE_SIZE >> 9);
 404
 405         r = kcopyd_get_pages(job->kc, nr_pages, &job->pages);
 406         if (!r) {
 407                 /* this job is ready for io */
 408                 push(&job->kc->io_jobs, job);
 409                 return 0;
 410         }
 411
 412         if (r == -ENOMEM)
 413                 /* can't complete now */
 414                 return 1;
 415
 416         return r;
 417 }
 418
 419 /*
 420  * Run through a list for as long as possible.  Returns the count
 421  * of successful jobs.
 422  */
 423 static int process_jobs(struct list_head *jobs, struct dm_kcopyd_client *kc,
 424                         int (*fn) (struct kcopyd_job *))
 425 {
 426         struct kcopyd_job *job;
 427         int r, count = 0;
 428
 429         while ((job = pop(jobs, kc))) {
 430
 431                 r = fn(job);
 432
 433                 if (r < 0) {
 434                         /* error this rogue job */
 435                         if (job->rw & WRITE)
 436                                 job->write_err = (unsigned long) -1L;
 437                         else
 438                                 job->read_err = 1;
 439                         push(&kc->complete_jobs, job);
 440                         break;
 441                 }
 442
 443                 if (r > 0) {
 444                         /*
 445                          * We couldn't service this job ATM, so
 446                          * push this job back onto the list.
 447                          */
 448                         push_head(jobs, job);
 449                         break;
 450                 }
 451
 452                 count++;
 453         }
 454
 455         return count;
 456 }
 457
 458 /*
 459  * kcopyd does this every time it's woken up.
 460  */
 461 static void do_work(struct work_struct *work)
 462 {
 463         struct dm_kcopyd_client *kc = container_of(work,
 464                                         struct dm_kcopyd_client, kcopyd_work);
 465         struct blk_plug plug;
 466
 467         /*
 468          * The order that these are called is *very* important.
 469          * complete jobs can free some pages for pages jobs.
 470          * Pages jobs when successful will jump onto the io jobs
 471          * list.  io jobs call wake when they complete and it all
 472          * starts again.
 473          */
 474         blk_start_plug(&plug);
 475         process_jobs(&kc->complete_jobs, kc, run_complete_job);
 476         process_jobs(&kc->pages_jobs, kc, run_pages_job);
 477         process_jobs(&kc->io_jobs, kc, run_io_job);
 478         blk_finish_plug(&plug);
 479 }
 480
 481 /*
 482  * If we are copying a small region we just dispatch a single job
 483  * to do the copy, otherwise the io has to be split up into many
 484  * jobs.
 485  */
 486 static void dispatch_job(struct kcopyd_job *job)
 487 {
 488         struct dm_kcopyd_client *kc = job->kc;
 489         atomic_inc(&kc->nr_jobs);
 490         if (unlikely(!job->source.count))
 491                 push(&kc->complete_jobs, job);
 492         else if (job->pages == &zero_page_list)
 493                 push(&kc->io_jobs, job);
 494         else
 495                 push(&kc->pages_jobs, job);
 496         wake(kc);
 497 }
 498
 499 static void segment_complete(int read_err, unsigned long write_err,
 500                              void *context)
 501 {
 502         /* FIXME: tidy this function */
 503         sector_t progress = 0;
 504         sector_t count = 0;
 505         struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
 506         struct kcopyd_job *job = sub_job->master_job;
 507         struct dm_kcopyd_client *kc = job->kc;
 508
 509         mutex_lock(&job->lock);
 510
 511         /* update the error */
 512         if (read_err)
 513                 job->read_err = 1;
 514
 515         if (write_err)
 516                 job->write_err |= write_err;
 517
 518         /*
 519          * Only dispatch more work if there hasn't been an error.
 520          */
 521         if ((!job->read_err && !job->write_err) ||
 522             test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags)) {
 523                 /* get the next chunk of work */
 524                 progress = job->progress;
 525                 count = job->source.count - progress;
 526                 if (count) {
 527                         if (count > SUB_JOB_SIZE)
 528                                 count = SUB_JOB_SIZE;
 529
 530                         job->progress += count;
 531                 }
 532         }
 533         mutex_unlock(&job->lock);
 534
 535         if (count) {
 536                 int i;
 537
 538                 *sub_job = *job;
 539                 sub_job->source.sector += progress;
 540                 sub_job->source.count = count;
 541
 542                 for (i = 0; i < job->num_dests; i++) {
 543                         sub_job->dests[i].sector += progress;
 544                         sub_job->dests[i].count = count;
 545                 }
 546
 547                 sub_job->fn = segment_complete;
 548                 sub_job->context = sub_job;
 549                 dispatch_job(sub_job);
 550
 551         } else if (atomic_dec_and_test(&job->sub_jobs)) {
 552
 553                 /*
 554                  * Queue the completion callback to the kcopyd thread.
 555                  *
 556                  * Some callers assume that all the completions are called
 557                  * from a single thread and don't race with each other.
 558                  *
 559                  * We must not call the callback directly here because this
 560                  * code may not be executing in the thread.
 561                  */
 562                 push(&kc->complete_jobs, job);
 563                 wake(kc);
 564         }
 565 }
 566
 567 /*
 568  * Create some sub jobs to share the work between them.
 569  */
 570 static void split_job(struct kcopyd_job *master_job)
 571 {
 572         int i;
 573
 574         atomic_inc(&master_job->kc->nr_jobs);
 575
 576         atomic_set(&master_job->sub_jobs, SPLIT_COUNT);
 577         for (i = 0; i < SPLIT_COUNT; i++) {
 578                 master_job[i + 1].master_job = master_job;
 579                 segment_complete(0, 0u, &master_job[i + 1]);
 580         }
 581 }
 582
 583 int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
 584                    unsigned int num_dests, struct dm_io_region *dests,
 585                    unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
 586 {
 587         struct kcopyd_job *job;
 588         int i;
 589
 590         /*
 591          * Allocate an array of jobs consisting of one master job
 592          * followed by SPLIT_COUNT sub jobs.
 593          */
 594         job = mempool_alloc(kc->job_pool, GFP_NOIO);
 595
 596         /*
 597          * set up for the read.
 598          */
 599         job->kc = kc;
 600         job->flags = flags;
 601         job->read_err = 0;
 602         job->write_err = 0;
 603
 604         job->num_dests = num_dests;
 605         memcpy(&job->dests, dests, sizeof(*dests) * num_dests);
 606
 607         if (from) {
 608                 job->source = *from;
 609                 job->pages = NULL;
 610                 job->rw = READ;
 611         } else {
 612                 memset(&job->source, 0, sizeof job->source);
 613                 job->source.count = job->dests[0].count;
 614                 job->pages = &zero_page_list;
 615
 616                 /*
 617                  * Use WRITE SAME to optimize zeroing if all dests support it.
 618                  */
 619                 job->rw = WRITE | REQ_WRITE_SAME;
 620                 for (i = 0; i < job->num_dests; i++)
 621                         if (!bdev_write_same(job->dests[i].bdev)) {
 622                                 job->rw = WRITE;
 623                                 break;
 624                         }
 625         }
 626
 627         job->fn = fn;
 628         job->context = context;
 629         job->master_job = job;
 630
 631         if (job->source.count <= SUB_JOB_SIZE)
 632                 dispatch_job(job);
 633         else {
 634                 mutex_init(&job->lock);
 635                 job->progress = 0;
 636                 split_job(job);
 637         }
 638
 639         return 0;
 640 }
 641 EXPORT_SYMBOL(dm_kcopyd_copy);
 642
 643 int dm_kcopyd_zero(struct dm_kcopyd_client *kc,
 644                    unsigned num_dests, struct dm_io_region *dests,
 645                    unsigned flags, dm_kcopyd_notify_fn fn, void *context)
 646 {
 647         return dm_kcopyd_copy(kc, NULL, num_dests, dests, flags, fn, context);
 648 }
 649 EXPORT_SYMBOL(dm_kcopyd_zero);
 650
 651 void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
 652                                  dm_kcopyd_notify_fn fn, void *context)
 653 {
 654         struct kcopyd_job *job;
 655
 656         job = mempool_alloc(kc->job_pool, GFP_NOIO);
 657
 658         memset(job, 0, sizeof(struct kcopyd_job));
 659         job->kc = kc;
 660         job->fn = fn;
 661         job->context = context;
 662         job->master_job = job;
 663
 664         atomic_inc(&kc->nr_jobs);
 665
 666         return job;
 667 }
 668 EXPORT_SYMBOL(dm_kcopyd_prepare_callback);
 669
 670 void dm_kcopyd_do_callback(void *j, int read_err, unsigned long write_err)
 671 {
 672         struct kcopyd_job *job = j;
 673         struct dm_kcopyd_client *kc = job->kc;
 674
 675         job->read_err = read_err;
 676         job->write_err = write_err;
 677
 678         push(&kc->complete_jobs, job);
 679         wake(kc);
 680 }
 681 EXPORT_SYMBOL(dm_kcopyd_do_callback);
 682
 683 /*
 684  * Cancels a kcopyd job, eg. someone might be deactivating a
 685  * mirror.
 686  */
 687 #if 0
 688 int kcopyd_cancel(struct kcopyd_job *job, int block)
 689 {
 690         /* FIXME: finish */
 691         return -1;
 692 }
 693 #endif  /*  0  */
 694
 695 /*-----------------------------------------------------------------
 696  * Client setup
 697  *---------------------------------------------------------------*/
 698 struct dm_kcopyd_client *dm_kcopyd_client_create(void)
 699 {
 700         int r = -ENOMEM;
 701         struct dm_kcopyd_client *kc;
 702
 703         kc = kmalloc(sizeof(*kc), GFP_KERNEL);
 704         if (!kc)
 705                 return ERR_PTR(-ENOMEM);
 706
 707         spin_lock_init(&kc->job_lock);
 708         INIT_LIST_HEAD(&kc->complete_jobs);
 709         INIT_LIST_HEAD(&kc->io_jobs);
 710         INIT_LIST_HEAD(&kc->pages_jobs);
 711
 712         kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
 713         if (!kc->job_pool)
 714                 goto bad_slab;
 715
 716         INIT_WORK(&kc->kcopyd_work, do_work);
 717         kc->kcopyd_wq = alloc_workqueue("kcopyd",
 718                                         WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);
 719         if (!kc->kcopyd_wq)
 720                 goto bad_workqueue;
 721
 722         kc->pages = NULL;
 723         kc->nr_reserved_pages = kc->nr_free_pages = 0;
 724         r = client_reserve_pages(kc, RESERVE_PAGES);
 725         if (r)
 726                 goto bad_client_pages;
 727
 728         kc->io_client = dm_io_client_create();
 729         if (IS_ERR(kc->io_client)) {
 730                 r = PTR_ERR(kc->io_client);
 731                 goto bad_io_client;
 732         }
 733
 734         init_waitqueue_head(&kc->destroyq);
 735         atomic_set(&kc->nr_jobs, 0);
 736
 737         return kc;
 738
 739 bad_io_client:
 740         client_free_pages(kc);
 741 bad_client_pages:
 742         destroy_workqueue(kc->kcopyd_wq);
 743 bad_workqueue:
 744         mempool_destroy(kc->job_pool);
 745 bad_slab:
 746         kfree(kc);
 747
 748         return ERR_PTR(r);
 749 }
 750 EXPORT_SYMBOL(dm_kcopyd_client_create);
 751
 752 void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc)
 753 {
 754         /* Wait for completion of all jobs submitted by this client. */
 755         wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs));
 756
 757         BUG_ON(!list_empty(&kc->complete_jobs));
 758         BUG_ON(!list_empty(&kc->io_jobs));
 759         BUG_ON(!list_empty(&kc->pages_jobs));
 760         destroy_workqueue(kc->kcopyd_wq);
 761         dm_io_client_destroy(kc->io_client);
 762         client_free_pages(kc);
 763         mempool_destroy(kc->job_pool);
 764         kfree(kc);
 765 }
 766 EXPORT_SYMBOL(dm_kcopyd_client_destroy);