drivers/staging/zram/zram_drv.c

   1 /*
   2  * Compressed RAM block device
   3  *
   4  * Copyright (C) 2008, 2009, 2010  Nitin Gupta
   5  *
   6  * This code is released using a dual license strategy: BSD/GPL
   7  * You can choose the licence that better fits your requirements.
   8  *
   9  * Released under the terms of 3-clause BSD License
  10  * Released under the terms of GNU General Public License Version 2.0
  11  *
  12  * Project home: http://compcache.googlecode.com
  13  */
  14
  15 #define KMSG_COMPONENT "zram"
  16 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
  17
  18 #ifdef CONFIG_ZRAM_DEBUG
  19 #define DEBUG
  20 #endif
  21
  22 #include <linux/module.h>
  23 #include <linux/kernel.h>
  24 #include <linux/bio.h>
  25 #include <linux/bitops.h>
  26 #include <linux/blkdev.h>
  27 #include <linux/buffer_head.h>
  28 #include <linux/device.h>
  29 #include <linux/genhd.h>
  30 #include <linux/highmem.h>
  31 #include <linux/slab.h>
  32 #include <linux/lzo.h>
  33 #include <linux/string.h>
  34 #include <linux/vmalloc.h>
  35
  36 #include "zram_drv.h"
  37
  38 /* Globals */
  39 static int zram_major;
  40 struct zram *zram_devices;
  41
  42 /* Module params (documentation at end) */
  43 static unsigned int num_devices = 1;
  44
  45 static void zram_stat64_add(struct zram *zram, u64 *v, u64 inc)
  46 {
  47         spin_lock(&zram->stat64_lock);
  48         *v = *v + inc;
  49         spin_unlock(&zram->stat64_lock);
  50 }
  51
  52 static void zram_stat64_sub(struct zram *zram, u64 *v, u64 dec)
  53 {
  54         spin_lock(&zram->stat64_lock);
  55         *v = *v - dec;
  56         spin_unlock(&zram->stat64_lock);
  57 }
  58
  59 static void zram_stat64_inc(struct zram *zram, u64 *v)
  60 {
  61         zram_stat64_add(zram, v, 1);
  62 }
  63
  64 static int zram_test_flag(struct zram *zram, u32 index,
  65                         enum zram_pageflags flag)
  66 {
  67         return zram->table[index].flags & BIT(flag);
  68 }
  69
  70 static void zram_set_flag(struct zram *zram, u32 index,
  71                         enum zram_pageflags flag)
  72 {
  73         zram->table[index].flags |= BIT(flag);
  74 }
  75
  76 static void zram_clear_flag(struct zram *zram, u32 index,
  77                         enum zram_pageflags flag)
  78 {
  79         zram->table[index].flags &= ~BIT(flag);
  80 }
  81
  82 static int page_zero_filled(void *ptr)
  83 {
  84         unsigned int pos;
  85         unsigned long *page;
  86
  87         page = (unsigned long *)ptr;
  88
  89         for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
  90                 if (page[pos])
  91                         return 0;
  92         }
  93
  94         return 1;
  95 }
  96
  97 static void zram_free_page(struct zram *zram, size_t index)
  98 {
  99         unsigned long handle = zram->table[index].handle;
 100         u16 size = zram->table[index].size;
 101
 102         if (unlikely(!handle)) {
 103                 /*
 104                  * No memory is allocated for zero filled pages.
 105                  * Simply clear zero page flag.
 106                  */
 107                 if (zram_test_flag(zram, index, ZRAM_ZERO)) {
 108                         zram_clear_flag(zram, index, ZRAM_ZERO);
 109                         zram->stats.pages_zero--;
 110                 }
 111                 return;
 112         }
 113
 114         if (unlikely(size > max_zpage_size))
 115                 zram->stats.bad_compress--;
 116
 117         zs_free(zram->mem_pool, handle);
 118
 119         if (size <= PAGE_SIZE / 2)
 120                 zram->stats.good_compress--;
 121
 122         zram_stat64_sub(zram, &zram->stats.compr_size,
 123                         zram->table[index].size);
 124         zram->stats.pages_stored--;
 125
 126         zram->table[index].handle = 0;
 127         zram->table[index].size = 0;
 128 }
 129
 130 static void handle_zero_page(struct bio_vec *bvec)
 131 {
 132         struct page *page = bvec->bv_page;
 133         void *user_mem;
 134
 135         user_mem = kmap_atomic(page);
 136         memset(user_mem + bvec->bv_offset, 0, bvec->bv_len);
 137         kunmap_atomic(user_mem);
 138
 139         flush_dcache_page(page);
 140 }
 141
 142 static inline int is_partial_io(struct bio_vec *bvec)
 143 {
 144         return bvec->bv_len != PAGE_SIZE;
 145 }
 146
 147 static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 148 {
 149         int ret = LZO_E_OK;
 150         size_t clen = PAGE_SIZE;
 151         unsigned char *cmem;
 152         unsigned long handle = zram->table[index].handle;
 153
 154         if (!handle || zram_test_flag(zram, index, ZRAM_ZERO)) {
 155                 memset(mem, 0, PAGE_SIZE);
 156                 return 0;
 157         }
 158
 159         cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 160         if (zram->table[index].size == PAGE_SIZE)
 161                 memcpy(mem, cmem, PAGE_SIZE);
 162         else
 163                 ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
 164                                                 mem, &clen);
 165         zs_unmap_object(zram->mem_pool, handle);
 166
 167         /* Should NEVER happen. Return bio error if it does. */
 168         if (unlikely(ret != LZO_E_OK)) {
 169                 pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 170                 zram_stat64_inc(zram, &zram->stats.failed_reads);
 171                 return ret;
 172         }
 173
 174         return 0;
 175 }
 176
 177 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 178                           u32 index, int offset, struct bio *bio)
 179 {
 180         int ret;
 181         struct page *page;
 182         unsigned char *user_mem, *uncmem = NULL;
 183
 184         page = bvec->bv_page;
 185
 186         if (unlikely(!zram->table[index].handle) ||
 187                         zram_test_flag(zram, index, ZRAM_ZERO)) {
 188                 handle_zero_page(bvec);
 189                 return 0;
 190         }
 191
 192         if (is_partial_io(bvec))
 193                 /* Use  a temporary buffer to decompress the page */
 194                 uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 195
 196         user_mem = kmap_atomic(page);
 197         if (!is_partial_io(bvec))
 198                 uncmem = user_mem;
 199
 200         if (!uncmem) {
 201                 pr_info("Unable to allocate temp memory\n");
 202                 ret = -ENOMEM;
 203                 goto out_cleanup;
 204         }
 205
 206         ret = zram_decompress_page(zram, uncmem, index);
 207         /* Should NEVER happen. Return bio error if it does. */
 208         if (unlikely(ret != LZO_E_OK)) {
 209                 pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 210                 zram_stat64_inc(zram, &zram->stats.failed_reads);
 211                 goto out_cleanup;
 212         }
 213
 214         if (is_partial_io(bvec))
 215                 memcpy(user_mem + bvec->bv_offset, uncmem + offset,
 216                                 bvec->bv_len);
 217
 218         flush_dcache_page(page);
 219         ret = 0;
 220 out_cleanup:
 221         kunmap_atomic(user_mem);
 222         if (is_partial_io(bvec))
 223                 kfree(uncmem);
 224         return ret;
 225 }
 226
 227 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 228                            int offset)
 229 {
 230         int ret = 0;
 231         size_t clen;
 232         unsigned long handle;
 233         struct page *page;
 234         unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
 235
 236         page = bvec->bv_page;
 237         src = zram->compress_buffer;
 238
 239         if (is_partial_io(bvec)) {
 240                 /*
 241                  * This is a partial IO. We need to read the full page
 242                  * before to write the changes.
 243                  */
 244                 uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 245                 if (!uncmem) {
 246                         pr_info("Error allocating temp memory!\n");
 247                         ret = -ENOMEM;
 248                         goto out;
 249                 }
 250                 ret = zram_decompress_page(zram, uncmem, index);
 251                 if (ret)
 252                         goto out;
 253         }
 254
 255         /*
 256          * System overwrites unused sectors. Free memory associated
 257          * with this sector now.
 258          */
 259         if (zram->table[index].handle ||
 260             zram_test_flag(zram, index, ZRAM_ZERO))
 261                 zram_free_page(zram, index);
 262
 263         user_mem = kmap_atomic(page);
 264
 265         if (is_partial_io(bvec)) {
 266                 memcpy(uncmem + offset, user_mem + bvec->bv_offset,
 267                        bvec->bv_len);
 268                 kunmap_atomic(user_mem);
 269                 user_mem = NULL;
 270         } else {
 271                 uncmem = user_mem;
 272         }
 273
 274         if (page_zero_filled(uncmem)) {
 275                 kunmap_atomic(user_mem);
 276                 if (is_partial_io(bvec))
 277                         kfree(uncmem);
 278                 zram->stats.pages_zero++;
 279                 zram_set_flag(zram, index, ZRAM_ZERO);
 280                 ret = 0;
 281                 goto out;
 282         }
 283
 284         ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
 285                                zram->compress_workmem);
 286
 287         if (!is_partial_io(bvec)) {
 288                 kunmap_atomic(user_mem);
 289                 user_mem = NULL;
 290                 uncmem = NULL;
 291         }
 292
 293         if (unlikely(ret != LZO_E_OK)) {
 294                 pr_err("Compression failed! err=%d\n", ret);
 295                 goto out;
 296         }
 297
 298         if (unlikely(clen > max_zpage_size)) {
 299                 zram->stats.bad_compress++;
 300                 clen = PAGE_SIZE;
 301                 src = NULL;
 302                 if (is_partial_io(bvec))
 303                         src = uncmem;
 304         }
 305
 306         handle = zs_malloc(zram->mem_pool, clen);
 307         if (!handle) {
 308                 pr_info("Error allocating memory for compressed "
 309                         "page: %u, size=%zu\n", index, clen);
 310                 ret = -ENOMEM;
 311                 goto out;
 312         }
 313         cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
 314
 315         if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 316                 src = kmap_atomic(page);
 317         memcpy(cmem, src, clen);
 318         if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 319                 kunmap_atomic(src);
 320
 321         zs_unmap_object(zram->mem_pool, handle);
 322
 323         zram->table[index].handle = handle;
 324         zram->table[index].size = clen;
 325
 326         /* Update stats */
 327         zram_stat64_add(zram, &zram->stats.compr_size, clen);
 328         zram->stats.pages_stored++;
 329         if (clen <= PAGE_SIZE / 2)
 330                 zram->stats.good_compress++;
 331
 332 out:
 333         if (is_partial_io(bvec))
 334                 kfree(uncmem);
 335
 336         if (ret)
 337                 zram_stat64_inc(zram, &zram->stats.failed_writes);
 338         return ret;
 339 }
 340
 341 static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 342                         int offset, struct bio *bio, int rw)
 343 {
 344         int ret;
 345
 346         if (rw == READ) {
 347                 down_read(&zram->lock);
 348                 ret = zram_bvec_read(zram, bvec, index, offset, bio);
 349                 up_read(&zram->lock);
 350         } else {
 351                 down_write(&zram->lock);
 352                 ret = zram_bvec_write(zram, bvec, index, offset);
 353                 up_write(&zram->lock);
 354         }
 355
 356         return ret;
 357 }
 358
 359 static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
 360 {
 361         if (*offset + bvec->bv_len >= PAGE_SIZE)
 362                 (*index)++;
 363         *offset = (*offset + bvec->bv_len) % PAGE_SIZE;
 364 }
 365
 366 static void __zram_make_request(struct zram *zram, struct bio *bio, int rw)
 367 {
 368         int i, offset;
 369         u32 index;
 370         struct bio_vec *bvec;
 371
 372         switch (rw) {
 373         case READ:
 374                 zram_stat64_inc(zram, &zram->stats.num_reads);
 375                 break;
 376         case WRITE:
 377                 zram_stat64_inc(zram, &zram->stats.num_writes);
 378                 break;
 379         }
 380
 381         index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
 382         offset = (bio->bi_sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
 383
 384         bio_for_each_segment(bvec, bio, i) {
 385                 int max_transfer_size = PAGE_SIZE - offset;
 386
 387                 if (bvec->bv_len > max_transfer_size) {
 388                         /*
 389                          * zram_bvec_rw() can only make operation on a single
 390                          * zram page. Split the bio vector.
 391                          */
 392                         struct bio_vec bv;
 393
 394                         bv.bv_page = bvec->bv_page;
 395                         bv.bv_len = max_transfer_size;
 396                         bv.bv_offset = bvec->bv_offset;
 397
 398                         if (zram_bvec_rw(zram, &bv, index, offset, bio, rw) < 0)
 399                                 goto out;
 400
 401                         bv.bv_len = bvec->bv_len - max_transfer_size;
 402                         bv.bv_offset += max_transfer_size;
 403                         if (zram_bvec_rw(zram, &bv, index+1, 0, bio, rw) < 0)
 404                                 goto out;
 405                 } else
 406                         if (zram_bvec_rw(zram, bvec, index, offset, bio, rw)
 407                             < 0)
 408                                 goto out;
 409
 410                 update_position(&index, &offset, bvec);
 411         }
 412
 413         set_bit(BIO_UPTODATE, &bio->bi_flags);
 414         bio_endio(bio, 0);
 415         return;
 416
 417 out:
 418         bio_io_error(bio);
 419 }
 420
 421 /*
 422  * Check if request is within bounds and aligned on zram logical blocks.
 423  */
 424 static inline int valid_io_request(struct zram *zram, struct bio *bio)
 425 {
 426         if (unlikely(
 427                 (bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
 428                 (bio->bi_sector & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)) ||
 429                 (bio->bi_size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))) {
 430
 431                 return 0;
 432         }
 433
 434         /* I/O request is valid */
 435         return 1;
 436 }
 437
 438 /*
 439  * Handler function for all zram I/O requests.
 440  */
 441 static void zram_make_request(struct request_queue *queue, struct bio *bio)
 442 {
 443         struct zram *zram = queue->queuedata;
 444
 445         down_read(&zram->init_lock);
 446         if (unlikely(!zram->init_done))
 447                 goto error;
 448
 449         if (!valid_io_request(zram, bio)) {
 450                 zram_stat64_inc(zram, &zram->stats.invalid_io);
 451                 goto error;
 452         }
 453
 454         __zram_make_request(zram, bio, bio_data_dir(bio));
 455         up_read(&zram->init_lock);
 456
 457         return;
 458
 459 error:
 460         up_read(&zram->init_lock);
 461         bio_io_error(bio);
 462 }
 463
 464 void __zram_reset_device(struct zram *zram)
 465 {
 466         size_t index;
 467
 468         if (!zram->init_done)
 469                 return;
 470
 471         zram->init_done = 0;
 472
 473         /* Free various per-device buffers */
 474         kfree(zram->compress_workmem);
 475         free_pages((unsigned long)zram->compress_buffer, 1);
 476
 477         zram->compress_workmem = NULL;
 478         zram->compress_buffer = NULL;
 479
 480         /* Free all pages that are still in this zram device */
 481         for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
 482                 unsigned long handle = zram->table[index].handle;
 483                 if (!handle)
 484                         continue;
 485
 486                 zs_free(zram->mem_pool, handle);
 487         }
 488
 489         vfree(zram->table);
 490         zram->table = NULL;
 491
 492         zs_destroy_pool(zram->mem_pool);
 493         zram->mem_pool = NULL;
 494
 495         /* Reset stats */
 496         memset(&zram->stats, 0, sizeof(zram->stats));
 497
 498         zram->disksize = 0;
 499         set_capacity(zram->disk, 0);
 500 }
 501
 502 void zram_reset_device(struct zram *zram)
 503 {
 504         down_write(&zram->init_lock);
 505         __zram_reset_device(zram);
 506         up_write(&zram->init_lock);
 507 }
 508
 509 /* zram->init_lock should be held */
 510 int zram_init_device(struct zram *zram)
 511 {
 512         int ret;
 513         size_t num_pages;
 514
 515         if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
 516                 pr_info(
 517                 "There is little point creating a zram of greater than "
 518                 "twice the size of memory since we expect a 2:1 compression "
 519                 "ratio. Note that zram uses about 0.1%% of the size of "
 520                 "the disk when not in use so a huge zram is "
 521                 "wasteful.\n"
 522                 "\tMemory Size: %lu kB\n"
 523                 "\tSize you selected: %llu kB\n"
 524                 "Continuing anyway ...\n",
 525                 (totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
 526                 );
 527         }
 528
 529         zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
 530         if (!zram->compress_workmem) {
 531                 pr_err("Error allocating compressor working memory!\n");
 532                 ret = -ENOMEM;
 533                 goto fail_no_table;
 534         }
 535
 536         zram->compress_buffer =
 537                 (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
 538         if (!zram->compress_buffer) {
 539                 pr_err("Error allocating compressor buffer space\n");
 540                 ret = -ENOMEM;
 541                 goto fail_no_table;
 542         }
 543
 544         num_pages = zram->disksize >> PAGE_SHIFT;
 545         zram->table = vzalloc(num_pages * sizeof(*zram->table));
 546         if (!zram->table) {
 547                 pr_err("Error allocating zram address table\n");
 548                 ret = -ENOMEM;
 549                 goto fail_no_table;
 550         }
 551
 552         /* zram devices sort of resembles non-rotational disks */
 553         queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 554
 555         zram->mem_pool = zs_create_pool(GFP_NOIO | __GFP_HIGHMEM);
 556         if (!zram->mem_pool) {
 557                 pr_err("Error creating memory pool\n");
 558                 ret = -ENOMEM;
 559                 goto fail;
 560         }
 561
 562         zram->init_done = 1;
 563
 564         pr_debug("Initialization done!\n");
 565         return 0;
 566
 567 fail_no_table:
 568         /* To prevent accessing table entries during cleanup */
 569         zram->disksize = 0;
 570 fail:
 571         __zram_reset_device(zram);
 572         pr_err("Initialization failed: err=%d\n", ret);
 573         return ret;
 574 }
 575
 576 static void zram_slot_free_notify(struct block_device *bdev,
 577                                 unsigned long index)
 578 {
 579         struct zram *zram;
 580
 581         zram = bdev->bd_disk->private_data;
 582         zram_free_page(zram, index);
 583         zram_stat64_inc(zram, &zram->stats.notify_free);
 584 }
 585
 586 static const struct block_device_operations zram_devops = {
 587         .swap_slot_free_notify = zram_slot_free_notify,
 588         .owner = THIS_MODULE
 589 };
 590
 591 static int create_device(struct zram *zram, int device_id)
 592 {
 593         int ret = 0;
 594
 595         init_rwsem(&zram->lock);
 596         init_rwsem(&zram->init_lock);
 597         spin_lock_init(&zram->stat64_lock);
 598
 599         zram->queue = blk_alloc_queue(GFP_KERNEL);
 600         if (!zram->queue) {
 601                 pr_err("Error allocating disk queue for device %d\n",
 602                         device_id);
 603                 ret = -ENOMEM;
 604                 goto out;
 605         }
 606
 607         blk_queue_make_request(zram->queue, zram_make_request);
 608         zram->queue->queuedata = zram;
 609
 610          /* gendisk structure */
 611         zram->disk = alloc_disk(1);
 612         if (!zram->disk) {
 613                 blk_cleanup_queue(zram->queue);
 614                 pr_warn("Error allocating disk structure for device %d\n",
 615                         device_id);
 616                 ret = -ENOMEM;
 617                 goto out;
 618         }
 619
 620         zram->disk->major = zram_major;
 621         zram->disk->first_minor = device_id;
 622         zram->disk->fops = &zram_devops;
 623         zram->disk->queue = zram->queue;
 624         zram->disk->private_data = zram;
 625         snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
 626
 627         /* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
 628         set_capacity(zram->disk, 0);
 629
 630         /*
 631          * To ensure that we always get PAGE_SIZE aligned
 632          * and n*PAGE_SIZED sized I/O requests.
 633          */
 634         blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
 635         blk_queue_logical_block_size(zram->disk->queue,
 636                                         ZRAM_LOGICAL_BLOCK_SIZE);
 637         blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
 638         blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
 639
 640         add_disk(zram->disk);
 641
 642         ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
 643                                 &zram_disk_attr_group);
 644         if (ret < 0) {
 645                 pr_warn("Error creating sysfs group");
 646                 goto out;
 647         }
 648
 649         zram->init_done = 0;
 650
 651 out:
 652         return ret;
 653 }
 654
 655 static void destroy_device(struct zram *zram)
 656 {
 657         sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
 658                         &zram_disk_attr_group);
 659
 660         if (zram->disk) {
 661                 del_gendisk(zram->disk);
 662                 put_disk(zram->disk);
 663         }
 664
 665         if (zram->queue)
 666                 blk_cleanup_queue(zram->queue);
 667 }
 668
 669 unsigned int zram_get_num_devices(void)
 670 {
 671         return num_devices;
 672 }
 673
 674 static int __init zram_init(void)
 675 {
 676         int ret, dev_id;
 677
 678         if (num_devices > max_num_devices) {
 679                 pr_warn("Invalid value for num_devices: %u\n",
 680                                 num_devices);
 681                 ret = -EINVAL;
 682                 goto out;
 683         }
 684
 685         zram_major = register_blkdev(0, "zram");
 686         if (zram_major <= 0) {
 687                 pr_warn("Unable to get major number\n");
 688                 ret = -EBUSY;
 689                 goto out;
 690         }
 691
 692         /* Allocate the device array and initialize each one */
 693         zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
 694         if (!zram_devices) {
 695                 ret = -ENOMEM;
 696                 goto unregister;
 697         }
 698
 699         for (dev_id = 0; dev_id < num_devices; dev_id++) {
 700                 ret = create_device(&zram_devices[dev_id], dev_id);
 701                 if (ret)
 702                         goto free_devices;
 703         }
 704
 705         pr_info("Created %u device(s) ...\n", num_devices);
 706
 707         return 0;
 708
 709 free_devices:
 710         while (dev_id)
 711                 destroy_device(&zram_devices[--dev_id]);
 712         kfree(zram_devices);
 713 unregister:
 714         unregister_blkdev(zram_major, "zram");
 715 out:
 716         return ret;
 717 }
 718
 719 static void __exit zram_exit(void)
 720 {
 721         int i;
 722         struct zram *zram;
 723
 724         for (i = 0; i < num_devices; i++) {
 725                 zram = &zram_devices[i];
 726
 727                 destroy_device(zram);
 728                 zram_reset_device(zram);
 729         }
 730
 731         unregister_blkdev(zram_major, "zram");
 732
 733         kfree(zram_devices);
 734         pr_debug("Cleanup done!\n");
 735 }
 736
 737 module_param(num_devices, uint, 0);
 738 MODULE_PARM_DESC(num_devices, "Number of zram devices");
 739
 740 module_init(zram_init);
 741 module_exit(zram_exit);
 742
 743 MODULE_LICENSE("Dual BSD/GPL");
 744 MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
 745 MODULE_DESCRIPTION("Compressed RAM Block Device");