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 *devices;
  41
  42 /* Module params (documentation at end) */
  43 unsigned int num_devices;
  44
  45 static void zram_stat_inc(u32 *v)
  46 {
  47         *v = *v + 1;
  48 }
  49
  50 static void zram_stat_dec(u32 *v)
  51 {
  52         *v = *v - 1;
  53 }
  54
  55 static void zram_stat64_add(struct zram *zram, u64 *v, u64 inc)
  56 {
  57         spin_lock(&zram->stat64_lock);
  58         *v = *v + inc;
  59         spin_unlock(&zram->stat64_lock);
  60 }
  61
  62 static void zram_stat64_sub(struct zram *zram, u64 *v, u64 dec)
  63 {
  64         spin_lock(&zram->stat64_lock);
  65         *v = *v - dec;
  66         spin_unlock(&zram->stat64_lock);
  67 }
  68
  69 static void zram_stat64_inc(struct zram *zram, u64 *v)
  70 {
  71         zram_stat64_add(zram, v, 1);
  72 }
  73
  74 static int zram_test_flag(struct zram *zram, u32 index,
  75                         enum zram_pageflags flag)
  76 {
  77         return zram->table[index].flags & BIT(flag);
  78 }
  79
  80 static void zram_set_flag(struct zram *zram, u32 index,
  81                         enum zram_pageflags flag)
  82 {
  83         zram->table[index].flags |= BIT(flag);
  84 }
  85
  86 static void zram_clear_flag(struct zram *zram, u32 index,
  87                         enum zram_pageflags flag)
  88 {
  89         zram->table[index].flags &= ~BIT(flag);
  90 }
  91
  92 static int page_zero_filled(void *ptr)
  93 {
  94         unsigned int pos;
  95         unsigned long *page;
  96
  97         page = (unsigned long *)ptr;
  98
  99         for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
 100                 if (page[pos])
 101                         return 0;
 102         }
 103
 104         return 1;
 105 }
 106
 107 static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
 108 {
 109         if (!zram->disksize) {
 110                 pr_info(
 111                 "disk size not provided. You can use disksize_kb module "
 112                 "param to specify size.\nUsing default: (%u%% of RAM).\n",
 113                 default_disksize_perc_ram
 114                 );
 115                 zram->disksize = default_disksize_perc_ram *
 116                                         (totalram_bytes / 100);
 117         }
 118
 119         if (zram->disksize > 2 * (totalram_bytes)) {
 120                 pr_info(
 121                 "There is little point creating a zram of greater than "
 122                 "twice the size of memory since we expect a 2:1 compression "
 123                 "ratio. Note that zram uses about 0.1%% of the size of "
 124                 "the disk when not in use so a huge zram is "
 125                 "wasteful.\n"
 126                 "\tMemory Size: %zu kB\n"
 127                 "\tSize you selected: %llu kB\n"
 128                 "Continuing anyway ...\n",
 129                 totalram_bytes >> 10, zram->disksize
 130                 );
 131         }
 132
 133         zram->disksize &= PAGE_MASK;
 134 }
 135
 136 static void zram_free_page(struct zram *zram, size_t index)
 137 {
 138         u32 clen;
 139         void *obj;
 140
 141         struct page *page = zram->table[index].page;
 142         u32 offset = zram->table[index].offset;
 143
 144         if (unlikely(!page)) {
 145                 /*
 146                  * No memory is allocated for zero filled pages.
 147                  * Simply clear zero page flag.
 148                  */
 149                 if (zram_test_flag(zram, index, ZRAM_ZERO)) {
 150                         zram_clear_flag(zram, index, ZRAM_ZERO);
 151                         zram_stat_dec(&zram->stats.pages_zero);
 152                 }
 153                 return;
 154         }
 155
 156         if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED))) {
 157                 clen = PAGE_SIZE;
 158                 __free_page(page);
 159                 zram_clear_flag(zram, index, ZRAM_UNCOMPRESSED);
 160                 zram_stat_dec(&zram->stats.pages_expand);
 161                 goto out;
 162         }
 163
 164         obj = kmap_atomic(page, KM_USER0) + offset;
 165         clen = xv_get_object_size(obj) - sizeof(struct zobj_header);
 166         kunmap_atomic(obj, KM_USER0);
 167
 168         xv_free(zram->mem_pool, page, offset);
 169         if (clen <= PAGE_SIZE / 2)
 170                 zram_stat_dec(&zram->stats.good_compress);
 171
 172 out:
 173         zram_stat64_sub(zram, &zram->stats.compr_size, clen);
 174         zram_stat_dec(&zram->stats.pages_stored);
 175
 176         zram->table[index].page = NULL;
 177         zram->table[index].offset = 0;
 178 }
 179
 180 static void handle_zero_page(struct page *page)
 181 {
 182         void *user_mem;
 183
 184         user_mem = kmap_atomic(page, KM_USER0);
 185         memset(user_mem, 0, PAGE_SIZE);
 186         kunmap_atomic(user_mem, KM_USER0);
 187
 188         flush_dcache_page(page);
 189 }
 190
 191 static void handle_uncompressed_page(struct zram *zram,
 192                                 struct page *page, u32 index)
 193 {
 194         unsigned char *user_mem, *cmem;
 195
 196         user_mem = kmap_atomic(page, KM_USER0);
 197         cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
 198                         zram->table[index].offset;
 199
 200         memcpy(user_mem, cmem, PAGE_SIZE);
 201         kunmap_atomic(user_mem, KM_USER0);
 202         kunmap_atomic(cmem, KM_USER1);
 203
 204         flush_dcache_page(page);
 205 }
 206
 207 static void zram_read(struct zram *zram, struct bio *bio)
 208 {
 209
 210         int i;
 211         u32 index;
 212         struct bio_vec *bvec;
 213
 214         zram_stat64_inc(zram, &zram->stats.num_reads);
 215         index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
 216
 217         bio_for_each_segment(bvec, bio, i) {
 218                 int ret;
 219                 size_t clen;
 220                 struct page *page;
 221                 struct zobj_header *zheader;
 222                 unsigned char *user_mem, *cmem;
 223
 224                 page = bvec->bv_page;
 225
 226                 if (zram_test_flag(zram, index, ZRAM_ZERO)) {
 227                         handle_zero_page(page);
 228                         index++;
 229                         continue;
 230                 }
 231
 232                 /* Requested page is not present in compressed area */
 233                 if (unlikely(!zram->table[index].page)) {
 234                         pr_debug("Read before write: sector=%lu, size=%u",
 235                                 (ulong)(bio->bi_sector), bio->bi_size);
 236                         handle_zero_page(page);
 237                         index++;
 238                         continue;
 239                 }
 240
 241                 /* Page is stored uncompressed since it's incompressible */
 242                 if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED))) {
 243                         handle_uncompressed_page(zram, page, index);
 244                         index++;
 245                         continue;
 246                 }
 247
 248                 user_mem = kmap_atomic(page, KM_USER0);
 249                 clen = PAGE_SIZE;
 250
 251                 cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
 252                                 zram->table[index].offset;
 253
 254                 ret = lzo1x_decompress_safe(
 255                         cmem + sizeof(*zheader),
 256                         xv_get_object_size(cmem) - sizeof(*zheader),
 257                         user_mem, &clen);
 258
 259                 kunmap_atomic(user_mem, KM_USER0);
 260                 kunmap_atomic(cmem, KM_USER1);
 261
 262                 /* Should NEVER happen. Return bio error if it does. */
 263                 if (unlikely(ret != LZO_E_OK)) {
 264                         pr_err("Decompression failed! err=%d, page=%u\n",
 265                                 ret, index);
 266                         zram_stat64_inc(zram, &zram->stats.failed_reads);
 267                         goto out;
 268                 }
 269
 270                 flush_dcache_page(page);
 271                 index++;
 272         }
 273
 274         set_bit(BIO_UPTODATE, &bio->bi_flags);
 275         bio_endio(bio, 0);
 276         return;
 277
 278 out:
 279         bio_io_error(bio);
 280 }
 281
 282 static void zram_write(struct zram *zram, struct bio *bio)
 283 {
 284         int i;
 285         u32 index;
 286         struct bio_vec *bvec;
 287
 288         zram_stat64_inc(zram, &zram->stats.num_writes);
 289         index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
 290
 291         bio_for_each_segment(bvec, bio, i) {
 292                 int ret;
 293                 u32 offset;
 294                 size_t clen;
 295                 struct zobj_header *zheader;
 296                 struct page *page, *page_store;
 297                 unsigned char *user_mem, *cmem, *src;
 298
 299                 page = bvec->bv_page;
 300                 src = zram->compress_buffer;
 301
 302                 /*
 303                  * System overwrites unused sectors. Free memory associated
 304                  * with this sector now.
 305                  */
 306                 if (zram->table[index].page ||
 307                                 zram_test_flag(zram, index, ZRAM_ZERO))
 308                         zram_free_page(zram, index);
 309
 310                 mutex_lock(&zram->lock);
 311
 312                 user_mem = kmap_atomic(page, KM_USER0);
 313                 if (page_zero_filled(user_mem)) {
 314                         kunmap_atomic(user_mem, KM_USER0);
 315                         mutex_unlock(&zram->lock);
 316                         zram_stat_inc(&zram->stats.pages_zero);
 317                         zram_set_flag(zram, index, ZRAM_ZERO);
 318                         index++;
 319                         continue;
 320                 }
 321
 322                 ret = lzo1x_1_compress(user_mem, PAGE_SIZE, src, &clen,
 323                                         zram->compress_workmem);
 324
 325                 kunmap_atomic(user_mem, KM_USER0);
 326
 327                 if (unlikely(ret != LZO_E_OK)) {
 328                         mutex_unlock(&zram->lock);
 329                         pr_err("Compression failed! err=%d\n", ret);
 330                         zram_stat64_inc(zram, &zram->stats.failed_writes);
 331                         goto out;
 332                 }
 333
 334                 /*
 335                  * Page is incompressible. Store it as-is (uncompressed)
 336                  * since we do not want to return too many disk write
 337                  * errors which has side effect of hanging the system.
 338                  */
 339                 if (unlikely(clen > max_zpage_size)) {
 340                         clen = PAGE_SIZE;
 341                         page_store = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
 342                         if (unlikely(!page_store)) {
 343                                 mutex_unlock(&zram->lock);
 344                                 pr_info("Error allocating memory for "
 345                                         "incompressible page: %u\n", index);
 346                                 zram_stat64_inc(zram,
 347                                         &zram->stats.failed_writes);
 348                                 goto out;
 349                         }
 350
 351                         offset = 0;
 352                         zram_set_flag(zram, index, ZRAM_UNCOMPRESSED);
 353                         zram_stat_inc(&zram->stats.pages_expand);
 354                         zram->table[index].page = page_store;
 355                         src = kmap_atomic(page, KM_USER0);
 356                         goto memstore;
 357                 }
 358
 359                 if (xv_malloc(zram->mem_pool, clen + sizeof(*zheader),
 360                                 &zram->table[index].page, &offset,
 361                                 GFP_NOIO | __GFP_HIGHMEM)) {
 362                         mutex_unlock(&zram->lock);
 363                         pr_info("Error allocating memory for compressed "
 364                                 "page: %u, size=%zu\n", index, clen);
 365                         zram_stat64_inc(zram, &zram->stats.failed_writes);
 366                         goto out;
 367                 }
 368
 369 memstore:
 370                 zram->table[index].offset = offset;
 371
 372                 cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
 373                                 zram->table[index].offset;
 374
 375 #if 0
 376                 /* Back-reference needed for memory defragmentation */
 377                 if (!zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)) {
 378                         zheader = (struct zobj_header *)cmem;
 379                         zheader->table_idx = index;
 380                         cmem += sizeof(*zheader);
 381                 }
 382 #endif
 383
 384                 memcpy(cmem, src, clen);
 385
 386                 kunmap_atomic(cmem, KM_USER1);
 387                 if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)))
 388                         kunmap_atomic(src, KM_USER0);
 389
 390                 /* Update stats */
 391                 zram_stat64_add(zram, &zram->stats.compr_size, clen);
 392                 zram_stat_inc(&zram->stats.pages_stored);
 393                 if (clen <= PAGE_SIZE / 2)
 394                         zram_stat_inc(&zram->stats.good_compress);
 395
 396                 mutex_unlock(&zram->lock);
 397                 index++;
 398         }
 399
 400         set_bit(BIO_UPTODATE, &bio->bi_flags);
 401         bio_endio(bio, 0);
 402         return;
 403
 404 out:
 405         bio_io_error(bio);
 406 }
 407
 408 /*
 409  * Check if request is within bounds and page aligned.
 410  */
 411 static inline int valid_io_request(struct zram *zram, struct bio *bio)
 412 {
 413         if (unlikely(
 414                 (bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
 415                 (bio->bi_sector & (SECTORS_PER_PAGE - 1)) ||
 416                 (bio->bi_size & (PAGE_SIZE - 1)))) {
 417
 418                 return 0;
 419         }
 420
 421         /* I/O request is valid */
 422         return 1;
 423 }
 424
 425 /*
 426  * Handler function for all zram I/O requests.
 427  */
 428 static int zram_make_request(struct request_queue *queue, struct bio *bio)
 429 {
 430         struct zram *zram = queue->queuedata;
 431
 432         if (!valid_io_request(zram, bio)) {
 433                 zram_stat64_inc(zram, &zram->stats.invalid_io);
 434                 bio_io_error(bio);
 435                 return 0;
 436         }
 437
 438         if (unlikely(!zram->init_done) && zram_init_device(zram)) {
 439                 bio_io_error(bio);
 440                 return 0;
 441         }
 442
 443         switch (bio_data_dir(bio)) {
 444         case READ:
 445                 zram_read(zram, bio);
 446                 break;
 447
 448         case WRITE:
 449                 zram_write(zram, bio);
 450                 break;
 451         }
 452
 453         return 0;
 454 }
 455
 456 void zram_reset_device(struct zram *zram)
 457 {
 458         size_t index;
 459
 460         mutex_lock(&zram->init_lock);
 461         zram->init_done = 0;
 462
 463         /* Free various per-device buffers */
 464         kfree(zram->compress_workmem);
 465         free_pages((unsigned long)zram->compress_buffer, 1);
 466
 467         zram->compress_workmem = NULL;
 468         zram->compress_buffer = NULL;
 469
 470         /* Free all pages that are still in this zram device */
 471         for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
 472                 struct page *page;
 473                 u16 offset;
 474
 475                 page = zram->table[index].page;
 476                 offset = zram->table[index].offset;
 477
 478                 if (!page)
 479                         continue;
 480
 481                 if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)))
 482                         __free_page(page);
 483                 else
 484                         xv_free(zram->mem_pool, page, offset);
 485         }
 486
 487         vfree(zram->table);
 488         zram->table = NULL;
 489
 490         xv_destroy_pool(zram->mem_pool);
 491         zram->mem_pool = NULL;
 492
 493         /* Reset stats */
 494         memset(&zram->stats, 0, sizeof(zram->stats));
 495
 496         zram->disksize = 0;
 497         mutex_unlock(&zram->init_lock);
 498 }
 499
 500 int zram_init_device(struct zram *zram)
 501 {
 502         int ret;
 503         size_t num_pages;
 504
 505         mutex_lock(&zram->init_lock);
 506
 507         if (zram->init_done) {
 508                 mutex_unlock(&zram->init_lock);
 509                 return 0;
 510         }
 511
 512         zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
 513
 514         zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
 515         if (!zram->compress_workmem) {
 516                 pr_err("Error allocating compressor working memory!\n");
 517                 ret = -ENOMEM;
 518                 goto fail;
 519         }
 520
 521         zram->compress_buffer = (void *)__get_free_pages(__GFP_ZERO, 1);
 522         if (!zram->compress_buffer) {
 523                 pr_err("Error allocating compressor buffer space\n");
 524                 ret = -ENOMEM;
 525                 goto fail;
 526         }
 527
 528         num_pages = zram->disksize >> PAGE_SHIFT;
 529         zram->table = vzalloc(num_pages * sizeof(*zram->table));
 530         if (!zram->table) {
 531                 pr_err("Error allocating zram address table\n");
 532                 /* To prevent accessing table entries during cleanup */
 533                 zram->disksize = 0;
 534                 ret = -ENOMEM;
 535                 goto fail;
 536         }
 537
 538         set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
 539
 540         /* zram devices sort of resembles non-rotational disks */
 541         queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 542
 543         zram->mem_pool = xv_create_pool();
 544         if (!zram->mem_pool) {
 545                 pr_err("Error creating memory pool\n");
 546                 ret = -ENOMEM;
 547                 goto fail;
 548         }
 549
 550         zram->init_done = 1;
 551         mutex_unlock(&zram->init_lock);
 552
 553         pr_debug("Initialization done!\n");
 554         return 0;
 555
 556 fail:
 557         mutex_unlock(&zram->init_lock);
 558         zram_reset_device(zram);
 559
 560         pr_err("Initialization failed: err=%d\n", ret);
 561         return ret;
 562 }
 563
 564 void zram_slot_free_notify(struct block_device *bdev, unsigned long index)
 565 {
 566         struct zram *zram;
 567
 568         zram = bdev->bd_disk->private_data;
 569         zram_free_page(zram, index);
 570         zram_stat64_inc(zram, &zram->stats.notify_free);
 571 }
 572
 573 static const struct block_device_operations zram_devops = {
 574         .swap_slot_free_notify = zram_slot_free_notify,
 575         .owner = THIS_MODULE
 576 };
 577
 578 static int create_device(struct zram *zram, int device_id)
 579 {
 580         int ret = 0;
 581
 582         mutex_init(&zram->lock);
 583         mutex_init(&zram->init_lock);
 584         spin_lock_init(&zram->stat64_lock);
 585
 586         zram->queue = blk_alloc_queue(GFP_KERNEL);
 587         if (!zram->queue) {
 588                 pr_err("Error allocating disk queue for device %d\n",
 589                         device_id);
 590                 ret = -ENOMEM;
 591                 goto out;
 592         }
 593
 594         blk_queue_make_request(zram->queue, zram_make_request);
 595         zram->queue->queuedata = zram;
 596
 597          /* gendisk structure */
 598         zram->disk = alloc_disk(1);
 599         if (!zram->disk) {
 600                 blk_cleanup_queue(zram->queue);
 601                 pr_warning("Error allocating disk structure for device %d\n",
 602                         device_id);
 603                 ret = -ENOMEM;
 604                 goto out;
 605         }
 606
 607         zram->disk->major = zram_major;
 608         zram->disk->first_minor = device_id;
 609         zram->disk->fops = &zram_devops;
 610         zram->disk->queue = zram->queue;
 611         zram->disk->private_data = zram;
 612         snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
 613
 614         /* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
 615         set_capacity(zram->disk, 0);
 616
 617         /*
 618          * To ensure that we always get PAGE_SIZE aligned
 619          * and n*PAGE_SIZED sized I/O requests.
 620          */
 621         blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
 622         blk_queue_logical_block_size(zram->disk->queue,
 623                                         ZRAM_LOGICAL_BLOCK_SIZE);
 624         blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
 625         blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
 626
 627         add_disk(zram->disk);
 628
 629         ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
 630                                 &zram_disk_attr_group);
 631         if (ret < 0) {
 632                 pr_warning("Error creating sysfs group");
 633                 goto out;
 634         }
 635
 636         zram->init_done = 0;
 637
 638 out:
 639         return ret;
 640 }
 641
 642 static void destroy_device(struct zram *zram)
 643 {
 644         sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
 645                         &zram_disk_attr_group);
 646
 647         if (zram->disk) {
 648                 del_gendisk(zram->disk);
 649                 put_disk(zram->disk);
 650         }
 651
 652         if (zram->queue)
 653                 blk_cleanup_queue(zram->queue);
 654 }
 655
 656 static int __init zram_init(void)
 657 {
 658         int ret, dev_id;
 659
 660         if (num_devices > max_num_devices) {
 661                 pr_warning("Invalid value for num_devices: %u\n",
 662                                 num_devices);
 663                 ret = -EINVAL;
 664                 goto out;
 665         }
 666
 667         zram_major = register_blkdev(0, "zram");
 668         if (zram_major <= 0) {
 669                 pr_warning("Unable to get major number\n");
 670                 ret = -EBUSY;
 671                 goto out;
 672         }
 673
 674         if (!num_devices) {
 675                 pr_info("num_devices not specified. Using default: 1\n");
 676                 num_devices = 1;
 677         }
 678
 679         /* Allocate the device array and initialize each one */
 680         pr_info("Creating %u devices ...\n", num_devices);
 681         devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
 682         if (!devices) {
 683                 ret = -ENOMEM;
 684                 goto unregister;
 685         }
 686
 687         for (dev_id = 0; dev_id < num_devices; dev_id++) {
 688                 ret = create_device(&devices[dev_id], dev_id);
 689                 if (ret)
 690                         goto free_devices;
 691         }
 692
 693         return 0;
 694
 695 free_devices:
 696         while (dev_id)
 697                 destroy_device(&devices[--dev_id]);
 698         kfree(devices);
 699 unregister:
 700         unregister_blkdev(zram_major, "zram");
 701 out:
 702         return ret;
 703 }
 704
 705 static void __exit zram_exit(void)
 706 {
 707         int i;
 708         struct zram *zram;
 709
 710         for (i = 0; i < num_devices; i++) {
 711                 zram = &devices[i];
 712
 713                 destroy_device(zram);
 714                 if (zram->init_done)
 715                         zram_reset_device(zram);
 716         }
 717
 718         unregister_blkdev(zram_major, "zram");
 719
 720         kfree(devices);
 721         pr_debug("Cleanup done!\n");
 722 }
 723
 724 module_param(num_devices, uint, 0);
 725 MODULE_PARM_DESC(num_devices, "Number of zram devices");
 726
 727 module_init(zram_init);
 728 module_exit(zram_exit);
 729
 730 MODULE_LICENSE("Dual BSD/GPL");
 731 MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
 732 MODULE_DESCRIPTION("Compressed RAM Block Device");