drivers/block/zram/zram_drv.c

   1 /*
   2  * Compressed RAM block device
   3  *
   4  * Copyright (C) 2008, 2009, 2010  Nitin Gupta
   5  *               2012, 2013 Minchan Kim
   6  *
   7  * This code is released using a dual license strategy: BSD/GPL
   8  * You can choose the licence that better fits your requirements.
   9  *
  10  * Released under the terms of 3-clause BSD License
  11  * Released under the terms of GNU General Public License Version 2.0
  12  *
  13  */
  14
  15 #define KMSG_COMPONENT "zram"
  16 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
  17
  18 #include <linux/module.h>
  19 #include <linux/kernel.h>
  20 #include <linux/bio.h>
  21 #include <linux/bitops.h>
  22 #include <linux/blkdev.h>
  23 #include <linux/buffer_head.h>
  24 #include <linux/device.h>
  25 #include <linux/genhd.h>
  26 #include <linux/highmem.h>
  27 #include <linux/slab.h>
  28 #include <linux/backing-dev.h>
  29 #include <linux/string.h>
  30 #include <linux/vmalloc.h>
  31 #include <linux/err.h>
  32 #include <linux/idr.h>
  33 #include <linux/sysfs.h>
  34 #include <linux/cpuhotplug.h>
  35
  36 #include "zram_drv.h"
  37
  38 static DEFINE_IDR(zram_index_idr);
  39 /* idr index must be protected */
  40 static DEFINE_MUTEX(zram_index_mutex);
  41
  42 static int zram_major;
  43 static const char *default_compressor = "lzo";
  44
  45 /* Module params (documentation at end) */
  46 static unsigned int num_devices = 1;
  47
  48 static void zram_free_page(struct zram *zram, size_t index);
  49
  50 static inline bool init_done(struct zram *zram)
  51 {
  52         return zram->disksize;
  53 }
  54
  55 static inline struct zram *dev_to_zram(struct device *dev)
  56 {
  57         return (struct zram *)dev_to_disk(dev)->private_data;
  58 }
  59
  60 static unsigned long zram_get_handle(struct zram *zram, u32 index)
  61 {
  62         return zram->table[index].handle;
  63 }
  64
  65 static void zram_set_handle(struct zram *zram, u32 index, unsigned long handle)
  66 {
  67         zram->table[index].handle = handle;
  68 }
  69
  70 /* flag operations require table entry bit_spin_lock() being held */
  71 static int zram_test_flag(struct zram *zram, u32 index,
  72                         enum zram_pageflags flag)
  73 {
  74         return zram->table[index].value & BIT(flag);
  75 }
  76
  77 static void zram_set_flag(struct zram *zram, u32 index,
  78                         enum zram_pageflags flag)
  79 {
  80         zram->table[index].value |= BIT(flag);
  81 }
  82
  83 static void zram_clear_flag(struct zram *zram, u32 index,
  84                         enum zram_pageflags flag)
  85 {
  86         zram->table[index].value &= ~BIT(flag);
  87 }
  88
  89 static inline void zram_set_element(struct zram *zram, u32 index,
  90                         unsigned long element)
  91 {
  92         zram->table[index].element = element;
  93 }
  94
  95 static unsigned long zram_get_element(struct zram *zram, u32 index)
  96 {
  97         return zram->table[index].element;
  98 }
  99
 100 static size_t zram_get_obj_size(struct zram *zram, u32 index)
 101 {
 102         return zram->table[index].value & (BIT(ZRAM_FLAG_SHIFT) - 1);
 103 }
 104
 105 static void zram_set_obj_size(struct zram *zram,
 106                                         u32 index, size_t size)
 107 {
 108         unsigned long flags = zram->table[index].value >> ZRAM_FLAG_SHIFT;
 109
 110         zram->table[index].value = (flags << ZRAM_FLAG_SHIFT) | size;
 111 }
 112
 113 #if PAGE_SIZE != 4096
 114 static inline bool is_partial_io(struct bio_vec *bvec)
 115 {
 116         return bvec->bv_len != PAGE_SIZE;
 117 }
 118 #else
 119 static inline bool is_partial_io(struct bio_vec *bvec)
 120 {
 121         return false;
 122 }
 123 #endif
 124
 125 static void zram_revalidate_disk(struct zram *zram)
 126 {
 127         revalidate_disk(zram->disk);
 128         /* revalidate_disk reset the BDI_CAP_STABLE_WRITES so set again */
 129         zram->disk->queue->backing_dev_info->capabilities |=
 130                 BDI_CAP_STABLE_WRITES;
 131 }
 132
 133 /*
 134  * Check if request is within bounds and aligned on zram logical blocks.
 135  */
 136 static inline bool valid_io_request(struct zram *zram,
 137                 sector_t start, unsigned int size)
 138 {
 139         u64 end, bound;
 140
 141         /* unaligned request */
 142         if (unlikely(start & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
 143                 return false;
 144         if (unlikely(size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
 145                 return false;
 146
 147         end = start + (size >> SECTOR_SHIFT);
 148         bound = zram->disksize >> SECTOR_SHIFT;
 149         /* out of range range */
 150         if (unlikely(start >= bound || end > bound || start > end))
 151                 return false;
 152
 153         /* I/O request is valid */
 154         return true;
 155 }
 156
 157 static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
 158 {
 159         *index  += (*offset + bvec->bv_len) / PAGE_SIZE;
 160         *offset = (*offset + bvec->bv_len) % PAGE_SIZE;
 161 }
 162
 163 static inline void update_used_max(struct zram *zram,
 164                                         const unsigned long pages)
 165 {
 166         unsigned long old_max, cur_max;
 167
 168         old_max = atomic_long_read(&zram->stats.max_used_pages);
 169
 170         do {
 171                 cur_max = old_max;
 172                 if (pages > cur_max)
 173                         old_max = atomic_long_cmpxchg(
 174                                 &zram->stats.max_used_pages, cur_max, pages);
 175         } while (old_max != cur_max);
 176 }
 177
 178 static inline void zram_fill_page(char *ptr, unsigned long len,
 179                                         unsigned long value)
 180 {
 181         int i;
 182         unsigned long *page = (unsigned long *)ptr;
 183
 184         WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
 185
 186         if (likely(value == 0)) {
 187                 memset(ptr, 0, len);
 188         } else {
 189                 for (i = 0; i < len / sizeof(*page); i++)
 190                         page[i] = value;
 191         }
 192 }
 193
 194 static bool page_same_filled(void *ptr, unsigned long *element)
 195 {
 196         unsigned int pos;
 197         unsigned long *page;
 198         unsigned long val;
 199
 200         page = (unsigned long *)ptr;
 201         val = page[0];
 202
 203         for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
 204                 if (val != page[pos])
 205                         return false;
 206         }
 207
 208         *element = val;
 209
 210         return true;
 211 }
 212
 213 static ssize_t initstate_show(struct device *dev,
 214                 struct device_attribute *attr, char *buf)
 215 {
 216         u32 val;
 217         struct zram *zram = dev_to_zram(dev);
 218
 219         down_read(&zram->init_lock);
 220         val = init_done(zram);
 221         up_read(&zram->init_lock);
 222
 223         return scnprintf(buf, PAGE_SIZE, "%u\n", val);
 224 }
 225
 226 static ssize_t disksize_show(struct device *dev,
 227                 struct device_attribute *attr, char *buf)
 228 {
 229         struct zram *zram = dev_to_zram(dev);
 230
 231         return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize);
 232 }
 233
 234 static ssize_t mem_limit_store(struct device *dev,
 235                 struct device_attribute *attr, const char *buf, size_t len)
 236 {
 237         u64 limit;
 238         char *tmp;
 239         struct zram *zram = dev_to_zram(dev);
 240
 241         limit = memparse(buf, &tmp);
 242         if (buf == tmp) /* no chars parsed, invalid input */
 243                 return -EINVAL;
 244
 245         down_write(&zram->init_lock);
 246         zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
 247         up_write(&zram->init_lock);
 248
 249         return len;
 250 }
 251
 252 static ssize_t mem_used_max_store(struct device *dev,
 253                 struct device_attribute *attr, const char *buf, size_t len)
 254 {
 255         int err;
 256         unsigned long val;
 257         struct zram *zram = dev_to_zram(dev);
 258
 259         err = kstrtoul(buf, 10, &val);
 260         if (err || val != 0)
 261                 return -EINVAL;
 262
 263         down_read(&zram->init_lock);
 264         if (init_done(zram)) {
 265                 atomic_long_set(&zram->stats.max_used_pages,
 266                                 zs_get_total_pages(zram->mem_pool));
 267         }
 268         up_read(&zram->init_lock);
 269
 270         return len;
 271 }
 272
 273 /*
 274  * We switched to per-cpu streams and this attr is not needed anymore.
 275  * However, we will keep it around for some time, because:
 276  * a) we may revert per-cpu streams in the future
 277  * b) it's visible to user space and we need to follow our 2 years
 278  *    retirement rule; but we already have a number of 'soon to be
 279  *    altered' attrs, so max_comp_streams need to wait for the next
 280  *    layoff cycle.
 281  */
 282 static ssize_t max_comp_streams_show(struct device *dev,
 283                 struct device_attribute *attr, char *buf)
 284 {
 285         return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus());
 286 }
 287
 288 static ssize_t max_comp_streams_store(struct device *dev,
 289                 struct device_attribute *attr, const char *buf, size_t len)
 290 {
 291         return len;
 292 }
 293
 294 static ssize_t comp_algorithm_show(struct device *dev,
 295                 struct device_attribute *attr, char *buf)
 296 {
 297         size_t sz;
 298         struct zram *zram = dev_to_zram(dev);
 299
 300         down_read(&zram->init_lock);
 301         sz = zcomp_available_show(zram->compressor, buf);
 302         up_read(&zram->init_lock);
 303
 304         return sz;
 305 }
 306
 307 static ssize_t comp_algorithm_store(struct device *dev,
 308                 struct device_attribute *attr, const char *buf, size_t len)
 309 {
 310         struct zram *zram = dev_to_zram(dev);
 311         char compressor[ARRAY_SIZE(zram->compressor)];
 312         size_t sz;
 313
 314         strlcpy(compressor, buf, sizeof(compressor));
 315         /* ignore trailing newline */
 316         sz = strlen(compressor);
 317         if (sz > 0 && compressor[sz - 1] == '\n')
 318                 compressor[sz - 1] = 0x00;
 319
 320         if (!zcomp_available_algorithm(compressor))
 321                 return -EINVAL;
 322
 323         down_write(&zram->init_lock);
 324         if (init_done(zram)) {
 325                 up_write(&zram->init_lock);
 326                 pr_info("Can't change algorithm for initialized device\n");
 327                 return -EBUSY;
 328         }
 329
 330         strcpy(zram->compressor, compressor);
 331         up_write(&zram->init_lock);
 332         return len;
 333 }
 334
 335 static ssize_t compact_store(struct device *dev,
 336                 struct device_attribute *attr, const char *buf, size_t len)
 337 {
 338         struct zram *zram = dev_to_zram(dev);
 339
 340         down_read(&zram->init_lock);
 341         if (!init_done(zram)) {
 342                 up_read(&zram->init_lock);
 343                 return -EINVAL;
 344         }
 345
 346         zs_compact(zram->mem_pool);
 347         up_read(&zram->init_lock);
 348
 349         return len;
 350 }
 351
 352 static ssize_t io_stat_show(struct device *dev,
 353                 struct device_attribute *attr, char *buf)
 354 {
 355         struct zram *zram = dev_to_zram(dev);
 356         ssize_t ret;
 357
 358         down_read(&zram->init_lock);
 359         ret = scnprintf(buf, PAGE_SIZE,
 360                         "%8llu %8llu %8llu %8llu\n",
 361                         (u64)atomic64_read(&zram->stats.failed_reads),
 362                         (u64)atomic64_read(&zram->stats.failed_writes),
 363                         (u64)atomic64_read(&zram->stats.invalid_io),
 364                         (u64)atomic64_read(&zram->stats.notify_free));
 365         up_read(&zram->init_lock);
 366
 367         return ret;
 368 }
 369
 370 static ssize_t mm_stat_show(struct device *dev,
 371                 struct device_attribute *attr, char *buf)
 372 {
 373         struct zram *zram = dev_to_zram(dev);
 374         struct zs_pool_stats pool_stats;
 375         u64 orig_size, mem_used = 0;
 376         long max_used;
 377         ssize_t ret;
 378
 379         memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats));
 380
 381         down_read(&zram->init_lock);
 382         if (init_done(zram)) {
 383                 mem_used = zs_get_total_pages(zram->mem_pool);
 384                 zs_pool_stats(zram->mem_pool, &pool_stats);
 385         }
 386
 387         orig_size = atomic64_read(&zram->stats.pages_stored);
 388         max_used = atomic_long_read(&zram->stats.max_used_pages);
 389
 390         ret = scnprintf(buf, PAGE_SIZE,
 391                         "%8llu %8llu %8llu %8lu %8ld %8llu %8lu\n",
 392                         orig_size << PAGE_SHIFT,
 393                         (u64)atomic64_read(&zram->stats.compr_data_size),
 394                         mem_used << PAGE_SHIFT,
 395                         zram->limit_pages << PAGE_SHIFT,
 396                         max_used << PAGE_SHIFT,
 397                         (u64)atomic64_read(&zram->stats.same_pages),
 398                         pool_stats.pages_compacted);
 399         up_read(&zram->init_lock);
 400
 401         return ret;
 402 }
 403
 404 static ssize_t debug_stat_show(struct device *dev,
 405                 struct device_attribute *attr, char *buf)
 406 {
 407         int version = 1;
 408         struct zram *zram = dev_to_zram(dev);
 409         ssize_t ret;
 410
 411         down_read(&zram->init_lock);
 412         ret = scnprintf(buf, PAGE_SIZE,
 413                         "version: %d\n%8llu\n",
 414                         version,
 415                         (u64)atomic64_read(&zram->stats.writestall));
 416         up_read(&zram->init_lock);
 417
 418         return ret;
 419 }
 420
 421 static DEVICE_ATTR_RO(io_stat);
 422 static DEVICE_ATTR_RO(mm_stat);
 423 static DEVICE_ATTR_RO(debug_stat);
 424
 425 static void zram_slot_lock(struct zram *zram, u32 index)
 426 {
 427         bit_spin_lock(ZRAM_ACCESS, &zram->table[index].value);
 428 }
 429
 430 static void zram_slot_unlock(struct zram *zram, u32 index)
 431 {
 432         bit_spin_unlock(ZRAM_ACCESS, &zram->table[index].value);
 433 }
 434
 435 static bool zram_same_page_read(struct zram *zram, u32 index,
 436                                 struct page *page,
 437                                 unsigned int offset, unsigned int len)
 438 {
 439         zram_slot_lock(zram, index);
 440         if (unlikely(!zram_get_handle(zram, index) ||
 441                         zram_test_flag(zram, index, ZRAM_SAME))) {
 442                 void *mem;
 443
 444                 zram_slot_unlock(zram, index);
 445                 mem = kmap_atomic(page);
 446                 zram_fill_page(mem + offset, len,
 447                                         zram_get_element(zram, index));
 448                 kunmap_atomic(mem);
 449                 return true;
 450         }
 451         zram_slot_unlock(zram, index);
 452
 453         return false;
 454 }
 455
 456 static bool zram_same_page_write(struct zram *zram, u32 index,
 457                                         struct page *page)
 458 {
 459         unsigned long element;
 460         void *mem = kmap_atomic(page);
 461
 462         if (page_same_filled(mem, &element)) {
 463                 kunmap_atomic(mem);
 464                 /* Free memory associated with this sector now. */
 465                 zram_slot_lock(zram, index);
 466                 zram_free_page(zram, index);
 467                 zram_set_flag(zram, index, ZRAM_SAME);
 468                 zram_set_element(zram, index, element);
 469                 zram_slot_unlock(zram, index);
 470
 471                 atomic64_inc(&zram->stats.same_pages);
 472                 atomic64_inc(&zram->stats.pages_stored);
 473                 return true;
 474         }
 475         kunmap_atomic(mem);
 476
 477         return false;
 478 }
 479
 480 static void zram_meta_free(struct zram *zram, u64 disksize)
 481 {
 482         size_t num_pages = disksize >> PAGE_SHIFT;
 483         size_t index;
 484
 485         /* Free all pages that are still in this zram device */
 486         for (index = 0; index < num_pages; index++)
 487                 zram_free_page(zram, index);
 488
 489         zs_destroy_pool(zram->mem_pool);
 490         vfree(zram->table);
 491 }
 492
 493 static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 494 {
 495         size_t num_pages;
 496
 497         num_pages = disksize >> PAGE_SHIFT;
 498         zram->table = vzalloc(num_pages * sizeof(*zram->table));
 499         if (!zram->table)
 500                 return false;
 501
 502         zram->mem_pool = zs_create_pool(zram->disk->disk_name);
 503         if (!zram->mem_pool) {
 504                 vfree(zram->table);
 505                 return false;
 506         }
 507
 508         return true;
 509 }
 510
 511 /*
 512  * To protect concurrent access to the same index entry,
 513  * caller should hold this table index entry's bit_spinlock to
 514  * indicate this index entry is accessing.
 515  */
 516 static void zram_free_page(struct zram *zram, size_t index)
 517 {
 518         unsigned long handle = zram_get_handle(zram, index);
 519
 520         /*
 521          * No memory is allocated for same element filled pages.
 522          * Simply clear same page flag.
 523          */
 524         if (zram_test_flag(zram, index, ZRAM_SAME)) {
 525                 zram_clear_flag(zram, index, ZRAM_SAME);
 526                 zram_set_element(zram, index, 0);
 527                 atomic64_dec(&zram->stats.same_pages);
 528                 atomic64_dec(&zram->stats.pages_stored);
 529                 return;
 530         }
 531
 532         if (!handle)
 533                 return;
 534
 535         zs_free(zram->mem_pool, handle);
 536
 537         atomic64_sub(zram_get_obj_size(zram, index),
 538                         &zram->stats.compr_data_size);
 539         atomic64_dec(&zram->stats.pages_stored);
 540
 541         zram_set_handle(zram, index, 0);
 542         zram_set_obj_size(zram, index, 0);
 543 }
 544
 545 static int zram_decompress_page(struct zram *zram, struct page *page, u32 index)
 546 {
 547         int ret;
 548         unsigned long handle;
 549         unsigned int size;
 550         void *src, *dst;
 551
 552         if (zram_same_page_read(zram, index, page, 0, PAGE_SIZE))
 553                 return 0;
 554
 555         zram_slot_lock(zram, index);
 556         handle = zram_get_handle(zram, index);
 557         size = zram_get_obj_size(zram, index);
 558
 559         src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 560         if (size == PAGE_SIZE) {
 561                 dst = kmap_atomic(page);
 562                 memcpy(dst, src, PAGE_SIZE);
 563                 kunmap_atomic(dst);
 564                 ret = 0;
 565         } else {
 566                 struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
 567
 568                 dst = kmap_atomic(page);
 569                 ret = zcomp_decompress(zstrm, src, size, dst);
 570                 kunmap_atomic(dst);
 571                 zcomp_stream_put(zram->comp);
 572         }
 573         zs_unmap_object(zram->mem_pool, handle);
 574         zram_slot_unlock(zram, index);
 575
 576         /* Should NEVER happen. Return bio error if it does. */
 577         if (unlikely(ret))
 578                 pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 579
 580         return ret;
 581 }
 582
 583 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 584                                 u32 index, int offset)
 585 {
 586         int ret;
 587         struct page *page;
 588
 589         page = bvec->bv_page;
 590         if (is_partial_io(bvec)) {
 591                 /* Use a temporary buffer to decompress the page */
 592                 page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
 593                 if (!page)
 594                         return -ENOMEM;
 595         }
 596
 597         ret = zram_decompress_page(zram, page, index);
 598         if (unlikely(ret))
 599                 goto out;
 600
 601         if (is_partial_io(bvec)) {
 602                 void *dst = kmap_atomic(bvec->bv_page);
 603                 void *src = kmap_atomic(page);
 604
 605                 memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len);
 606                 kunmap_atomic(src);
 607                 kunmap_atomic(dst);
 608         }
 609 out:
 610         if (is_partial_io(bvec))
 611                 __free_page(page);
 612
 613         return ret;
 614 }
 615
 616 static int zram_compress(struct zram *zram, struct zcomp_strm **zstrm,
 617                         struct page *page,
 618                         unsigned long *out_handle, unsigned int *out_comp_len)
 619 {
 620         int ret;
 621         unsigned int comp_len;
 622         void *src;
 623         unsigned long alloced_pages;
 624         unsigned long handle = 0;
 625
 626 compress_again:
 627         src = kmap_atomic(page);
 628         ret = zcomp_compress(*zstrm, src, &comp_len);
 629         kunmap_atomic(src);
 630
 631         if (unlikely(ret)) {
 632                 pr_err("Compression failed! err=%d\n", ret);
 633                 if (handle)
 634                         zs_free(zram->mem_pool, handle);
 635                 return ret;
 636         }
 637
 638         if (unlikely(comp_len > max_zpage_size))
 639                 comp_len = PAGE_SIZE;
 640
 641         /*
 642          * handle allocation has 2 paths:
 643          * a) fast path is executed with preemption disabled (for
 644          *  per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
 645          *  since we can't sleep;
 646          * b) slow path enables preemption and attempts to allocate
 647          *  the page with __GFP_DIRECT_RECLAIM bit set. we have to
 648          *  put per-cpu compression stream and, thus, to re-do
 649          *  the compression once handle is allocated.
 650          *
 651          * if we have a 'non-null' handle here then we are coming
 652          * from the slow path and handle has already been allocated.
 653          */
 654         if (!handle)
 655                 handle = zs_malloc(zram->mem_pool, comp_len,
 656                                 __GFP_KSWAPD_RECLAIM |
 657                                 __GFP_NOWARN |
 658                                 __GFP_HIGHMEM |
 659                                 __GFP_MOVABLE);
 660         if (!handle) {
 661                 zcomp_stream_put(zram->comp);
 662                 atomic64_inc(&zram->stats.writestall);
 663                 handle = zs_malloc(zram->mem_pool, comp_len,
 664                                 GFP_NOIO | __GFP_HIGHMEM |
 665                                 __GFP_MOVABLE);
 666                 *zstrm = zcomp_stream_get(zram->comp);
 667                 if (handle)
 668                         goto compress_again;
 669                 return -ENOMEM;
 670         }
 671
 672         alloced_pages = zs_get_total_pages(zram->mem_pool);
 673         update_used_max(zram, alloced_pages);
 674
 675         if (zram->limit_pages && alloced_pages > zram->limit_pages) {
 676                 zs_free(zram->mem_pool, handle);
 677                 return -ENOMEM;
 678         }
 679
 680         *out_handle = handle;
 681         *out_comp_len = comp_len;
 682         return 0;
 683 }
 684
 685 static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
 686 {
 687         int ret;
 688         unsigned long handle;
 689         unsigned int comp_len;
 690         void *src, *dst;
 691         struct zcomp_strm *zstrm;
 692         struct page *page = bvec->bv_page;
 693
 694         if (zram_same_page_write(zram, index, page))
 695                 return 0;
 696
 697         zstrm = zcomp_stream_get(zram->comp);
 698         ret = zram_compress(zram, &zstrm, page, &handle, &comp_len);
 699         if (ret) {
 700                 zcomp_stream_put(zram->comp);
 701                 return ret;
 702         }
 703
 704         dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
 705
 706         src = zstrm->buffer;
 707         if (comp_len == PAGE_SIZE)
 708                 src = kmap_atomic(page);
 709         memcpy(dst, src, comp_len);
 710         if (comp_len == PAGE_SIZE)
 711                 kunmap_atomic(src);
 712
 713         zcomp_stream_put(zram->comp);
 714         zs_unmap_object(zram->mem_pool, handle);
 715
 716         /*
 717          * Free memory associated with this sector
 718          * before overwriting unused sectors.
 719          */
 720         zram_slot_lock(zram, index);
 721         zram_free_page(zram, index);
 722         zram_set_handle(zram, index, handle);
 723         zram_set_obj_size(zram, index, comp_len);
 724         zram_slot_unlock(zram, index);
 725
 726         /* Update stats */
 727         atomic64_add(comp_len, &zram->stats.compr_data_size);
 728         atomic64_inc(&zram->stats.pages_stored);
 729         return 0;
 730 }
 731
 732 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 733                                 u32 index, int offset)
 734 {
 735         int ret;
 736         struct page *page = NULL;
 737         void *src;
 738         struct bio_vec vec;
 739
 740         vec = *bvec;
 741         if (is_partial_io(bvec)) {
 742                 void *dst;
 743                 /*
 744                  * This is a partial IO. We need to read the full page
 745                  * before to write the changes.
 746                  */
 747                 page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
 748                 if (!page)
 749                         return -ENOMEM;
 750
 751                 ret = zram_decompress_page(zram, page, index);
 752                 if (ret)
 753                         goto out;
 754
 755                 src = kmap_atomic(bvec->bv_page);
 756                 dst = kmap_atomic(page);
 757                 memcpy(dst + offset, src + bvec->bv_offset, bvec->bv_len);
 758                 kunmap_atomic(dst);
 759                 kunmap_atomic(src);
 760
 761                 vec.bv_page = page;
 762                 vec.bv_len = PAGE_SIZE;
 763                 vec.bv_offset = 0;
 764         }
 765
 766         ret = __zram_bvec_write(zram, &vec, index);
 767 out:
 768         if (is_partial_io(bvec))
 769                 __free_page(page);
 770         return ret;
 771 }
 772
 773 /*
 774  * zram_bio_discard - handler on discard request
 775  * @index: physical block index in PAGE_SIZE units
 776  * @offset: byte offset within physical block
 777  */
 778 static void zram_bio_discard(struct zram *zram, u32 index,
 779                              int offset, struct bio *bio)
 780 {
 781         size_t n = bio->bi_iter.bi_size;
 782
 783         /*
 784          * zram manages data in physical block size units. Because logical block
 785          * size isn't identical with physical block size on some arch, we
 786          * could get a discard request pointing to a specific offset within a
 787          * certain physical block.  Although we can handle this request by
 788          * reading that physiclal block and decompressing and partially zeroing
 789          * and re-compressing and then re-storing it, this isn't reasonable
 790          * because our intent with a discard request is to save memory.  So
 791          * skipping this logical block is appropriate here.
 792          */
 793         if (offset) {
 794                 if (n <= (PAGE_SIZE - offset))
 795                         return;
 796
 797                 n -= (PAGE_SIZE - offset);
 798                 index++;
 799         }
 800
 801         while (n >= PAGE_SIZE) {
 802                 zram_slot_lock(zram, index);
 803                 zram_free_page(zram, index);
 804                 zram_slot_unlock(zram, index);
 805                 atomic64_inc(&zram->stats.notify_free);
 806                 index++;
 807                 n -= PAGE_SIZE;
 808         }
 809 }
 810
 811 static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 812                         int offset, bool is_write)
 813 {
 814         unsigned long start_time = jiffies;
 815         int rw_acct = is_write ? REQ_OP_WRITE : REQ_OP_READ;
 816         int ret;
 817
 818         generic_start_io_acct(rw_acct, bvec->bv_len >> SECTOR_SHIFT,
 819                         &zram->disk->part0);
 820
 821         if (!is_write) {
 822                 atomic64_inc(&zram->stats.num_reads);
 823                 ret = zram_bvec_read(zram, bvec, index, offset);
 824                 flush_dcache_page(bvec->bv_page);
 825         } else {
 826                 atomic64_inc(&zram->stats.num_writes);
 827                 ret = zram_bvec_write(zram, bvec, index, offset);
 828         }
 829
 830         generic_end_io_acct(rw_acct, &zram->disk->part0, start_time);
 831
 832         if (unlikely(ret)) {
 833                 if (!is_write)
 834                         atomic64_inc(&zram->stats.failed_reads);
 835                 else
 836                         atomic64_inc(&zram->stats.failed_writes);
 837         }
 838
 839         return ret;
 840 }
 841
 842 static void __zram_make_request(struct zram *zram, struct bio *bio)
 843 {
 844         int offset;
 845         u32 index;
 846         struct bio_vec bvec;
 847         struct bvec_iter iter;
 848
 849         index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
 850         offset = (bio->bi_iter.bi_sector &
 851                   (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
 852
 853         switch (bio_op(bio)) {
 854         case REQ_OP_DISCARD:
 855         case REQ_OP_WRITE_ZEROES:
 856                 zram_bio_discard(zram, index, offset, bio);
 857                 bio_endio(bio);
 858                 return;
 859         default:
 860                 break;
 861         }
 862
 863         bio_for_each_segment(bvec, bio, iter) {
 864                 struct bio_vec bv = bvec;
 865                 unsigned int unwritten = bvec.bv_len;
 866
 867                 do {
 868                         bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
 869                                                         unwritten);
 870                         if (zram_bvec_rw(zram, &bv, index, offset,
 871                                         op_is_write(bio_op(bio))) < 0)
 872                                 goto out;
 873
 874                         bv.bv_offset += bv.bv_len;
 875                         unwritten -= bv.bv_len;
 876
 877                         update_position(&index, &offset, &bv);
 878                 } while (unwritten);
 879         }
 880
 881         bio_endio(bio);
 882         return;
 883
 884 out:
 885         bio_io_error(bio);
 886 }
 887
 888 /*
 889  * Handler function for all zram I/O requests.
 890  */
 891 static blk_qc_t zram_make_request(struct request_queue *queue, struct bio *bio)
 892 {
 893         struct zram *zram = queue->queuedata;
 894
 895         if (!valid_io_request(zram, bio->bi_iter.bi_sector,
 896                                         bio->bi_iter.bi_size)) {
 897                 atomic64_inc(&zram->stats.invalid_io);
 898                 goto error;
 899         }
 900
 901         __zram_make_request(zram, bio);
 902         return BLK_QC_T_NONE;
 903
 904 error:
 905         bio_io_error(bio);
 906         return BLK_QC_T_NONE;
 907 }
 908
 909 static void zram_slot_free_notify(struct block_device *bdev,
 910                                 unsigned long index)
 911 {
 912         struct zram *zram;
 913
 914         zram = bdev->bd_disk->private_data;
 915
 916         zram_slot_lock(zram, index);
 917         zram_free_page(zram, index);
 918         zram_slot_unlock(zram, index);
 919         atomic64_inc(&zram->stats.notify_free);
 920 }
 921
 922 static int zram_rw_page(struct block_device *bdev, sector_t sector,
 923                        struct page *page, bool is_write)
 924 {
 925         int offset, err = -EIO;
 926         u32 index;
 927         struct zram *zram;
 928         struct bio_vec bv;
 929
 930         zram = bdev->bd_disk->private_data;
 931
 932         if (!valid_io_request(zram, sector, PAGE_SIZE)) {
 933                 atomic64_inc(&zram->stats.invalid_io);
 934                 err = -EINVAL;
 935                 goto out;
 936         }
 937
 938         index = sector >> SECTORS_PER_PAGE_SHIFT;
 939         offset = (sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
 940
 941         bv.bv_page = page;
 942         bv.bv_len = PAGE_SIZE;
 943         bv.bv_offset = 0;
 944
 945         err = zram_bvec_rw(zram, &bv, index, offset, is_write);
 946 out:
 947         /*
 948          * If I/O fails, just return error(ie, non-zero) without
 949          * calling page_endio.
 950          * It causes resubmit the I/O with bio request by upper functions
 951          * of rw_page(e.g., swap_readpage, __swap_writepage) and
 952          * bio->bi_end_io does things to handle the error
 953          * (e.g., SetPageError, set_page_dirty and extra works).
 954          */
 955         if (err == 0)
 956                 page_endio(page, is_write, 0);
 957         return err;
 958 }
 959
 960 static void zram_reset_device(struct zram *zram)
 961 {
 962         struct zcomp *comp;
 963         u64 disksize;
 964
 965         down_write(&zram->init_lock);
 966
 967         zram->limit_pages = 0;
 968
 969         if (!init_done(zram)) {
 970                 up_write(&zram->init_lock);
 971                 return;
 972         }
 973
 974         comp = zram->comp;
 975         disksize = zram->disksize;
 976         zram->disksize = 0;
 977
 978         set_capacity(zram->disk, 0);
 979         part_stat_set_all(&zram->disk->part0, 0);
 980
 981         up_write(&zram->init_lock);
 982         /* I/O operation under all of CPU are done so let's free */
 983         zram_meta_free(zram, disksize);
 984         memset(&zram->stats, 0, sizeof(zram->stats));
 985         zcomp_destroy(comp);
 986 }
 987
 988 static ssize_t disksize_store(struct device *dev,
 989                 struct device_attribute *attr, const char *buf, size_t len)
 990 {
 991         u64 disksize;
 992         struct zcomp *comp;
 993         struct zram *zram = dev_to_zram(dev);
 994         int err;
 995
 996         disksize = memparse(buf, NULL);
 997         if (!disksize)
 998                 return -EINVAL;
 999
1000         down_write(&zram->init_lock);
1001         if (init_done(zram)) {
1002                 pr_info("Cannot change disksize for initialized device\n");
1003                 err = -EBUSY;
1004                 goto out_unlock;
1005         }
1006
1007         disksize = PAGE_ALIGN(disksize);
1008         if (!zram_meta_alloc(zram, disksize)) {
1009                 err = -ENOMEM;
1010                 goto out_unlock;
1011         }
1012
1013         comp = zcomp_create(zram->compressor);
1014         if (IS_ERR(comp)) {
1015                 pr_err("Cannot initialise %s compressing backend\n",
1016                                 zram->compressor);
1017                 err = PTR_ERR(comp);
1018                 goto out_free_meta;
1019         }
1020
1021         zram->comp = comp;
1022         zram->disksize = disksize;
1023         set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
1024         zram_revalidate_disk(zram);
1025         up_write(&zram->init_lock);
1026
1027         return len;
1028
1029 out_free_meta:
1030         zram_meta_free(zram, disksize);
1031 out_unlock:
1032         up_write(&zram->init_lock);
1033         return err;
1034 }
1035
1036 static ssize_t reset_store(struct device *dev,
1037                 struct device_attribute *attr, const char *buf, size_t len)
1038 {
1039         int ret;
1040         unsigned short do_reset;
1041         struct zram *zram;
1042         struct block_device *bdev;
1043
1044         ret = kstrtou16(buf, 10, &do_reset);
1045         if (ret)
1046                 return ret;
1047
1048         if (!do_reset)
1049                 return -EINVAL;
1050
1051         zram = dev_to_zram(dev);
1052         bdev = bdget_disk(zram->disk, 0);
1053         if (!bdev)
1054                 return -ENOMEM;
1055
1056         mutex_lock(&bdev->bd_mutex);
1057         /* Do not reset an active device or claimed device */
1058         if (bdev->bd_openers || zram->claim) {
1059                 mutex_unlock(&bdev->bd_mutex);
1060                 bdput(bdev);
1061                 return -EBUSY;
1062         }
1063
1064         /* From now on, anyone can't open /dev/zram[0-9] */
1065         zram->claim = true;
1066         mutex_unlock(&bdev->bd_mutex);
1067
1068         /* Make sure all the pending I/O are finished */
1069         fsync_bdev(bdev);
1070         zram_reset_device(zram);
1071         zram_revalidate_disk(zram);
1072         bdput(bdev);
1073
1074         mutex_lock(&bdev->bd_mutex);
1075         zram->claim = false;
1076         mutex_unlock(&bdev->bd_mutex);
1077
1078         return len;
1079 }
1080
1081 static int zram_open(struct block_device *bdev, fmode_t mode)
1082 {
1083         int ret = 0;
1084         struct zram *zram;
1085
1086         WARN_ON(!mutex_is_locked(&bdev->bd_mutex));
1087
1088         zram = bdev->bd_disk->private_data;
1089         /* zram was claimed to reset so open request fails */
1090         if (zram->claim)
1091                 ret = -EBUSY;
1092
1093         return ret;
1094 }
1095
1096 static const struct block_device_operations zram_devops = {
1097         .open = zram_open,
1098         .swap_slot_free_notify = zram_slot_free_notify,
1099         .rw_page = zram_rw_page,
1100         .owner = THIS_MODULE
1101 };
1102
1103 static DEVICE_ATTR_WO(compact);
1104 static DEVICE_ATTR_RW(disksize);
1105 static DEVICE_ATTR_RO(initstate);
1106 static DEVICE_ATTR_WO(reset);
1107 static DEVICE_ATTR_WO(mem_limit);
1108 static DEVICE_ATTR_WO(mem_used_max);
1109 static DEVICE_ATTR_RW(max_comp_streams);
1110 static DEVICE_ATTR_RW(comp_algorithm);
1111
1112 static struct attribute *zram_disk_attrs[] = {
1113         &dev_attr_disksize.attr,
1114         &dev_attr_initstate.attr,
1115         &dev_attr_reset.attr,
1116         &dev_attr_compact.attr,
1117         &dev_attr_mem_limit.attr,
1118         &dev_attr_mem_used_max.attr,
1119         &dev_attr_max_comp_streams.attr,
1120         &dev_attr_comp_algorithm.attr,
1121         &dev_attr_io_stat.attr,
1122         &dev_attr_mm_stat.attr,
1123         &dev_attr_debug_stat.attr,
1124         NULL,
1125 };
1126
1127 static const struct attribute_group zram_disk_attr_group = {
1128         .attrs = zram_disk_attrs,
1129 };
1130
1131 /*
1132  * Allocate and initialize new zram device. the function returns
1133  * '>= 0' device_id upon success, and negative value otherwise.
1134  */
1135 static int zram_add(void)
1136 {
1137         struct zram *zram;
1138         struct request_queue *queue;
1139         int ret, device_id;
1140
1141         zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
1142         if (!zram)
1143                 return -ENOMEM;
1144
1145         ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
1146         if (ret < 0)
1147                 goto out_free_dev;
1148         device_id = ret;
1149
1150         init_rwsem(&zram->init_lock);
1151
1152         queue = blk_alloc_queue(GFP_KERNEL);
1153         if (!queue) {
1154                 pr_err("Error allocating disk queue for device %d\n",
1155                         device_id);
1156                 ret = -ENOMEM;
1157                 goto out_free_idr;
1158         }
1159
1160         blk_queue_make_request(queue, zram_make_request);
1161
1162         /* gendisk structure */
1163         zram->disk = alloc_disk(1);
1164         if (!zram->disk) {
1165                 pr_err("Error allocating disk structure for device %d\n",
1166                         device_id);
1167                 ret = -ENOMEM;
1168                 goto out_free_queue;
1169         }
1170
1171         zram->disk->major = zram_major;
1172         zram->disk->first_minor = device_id;
1173         zram->disk->fops = &zram_devops;
1174         zram->disk->queue = queue;
1175         zram->disk->queue->queuedata = zram;
1176         zram->disk->private_data = zram;
1177         snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
1178
1179         /* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
1180         set_capacity(zram->disk, 0);
1181         /* zram devices sort of resembles non-rotational disks */
1182         queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
1183         queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, zram->disk->queue);
1184         /*
1185          * To ensure that we always get PAGE_SIZE aligned
1186          * and n*PAGE_SIZED sized I/O requests.
1187          */
1188         blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
1189         blk_queue_logical_block_size(zram->disk->queue,
1190                                         ZRAM_LOGICAL_BLOCK_SIZE);
1191         blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
1192         blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
1193         zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
1194         blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);
1195         queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);
1196
1197         /*
1198          * zram_bio_discard() will clear all logical blocks if logical block
1199          * size is identical with physical block size(PAGE_SIZE). But if it is
1200          * different, we will skip discarding some parts of logical blocks in
1201          * the part of the request range which isn't aligned to physical block
1202          * size.  So we can't ensure that all discarded logical blocks are
1203          * zeroed.
1204          */
1205         if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
1206                 blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
1207
1208         add_disk(zram->disk);
1209
1210         ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
1211                                 &zram_disk_attr_group);
1212         if (ret < 0) {
1213                 pr_err("Error creating sysfs group for device %d\n",
1214                                 device_id);
1215                 goto out_free_disk;
1216         }
1217         strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
1218
1219         pr_info("Added device: %s\n", zram->disk->disk_name);
1220         return device_id;
1221
1222 out_free_disk:
1223         del_gendisk(zram->disk);
1224         put_disk(zram->disk);
1225 out_free_queue:
1226         blk_cleanup_queue(queue);
1227 out_free_idr:
1228         idr_remove(&zram_index_idr, device_id);
1229 out_free_dev:
1230         kfree(zram);
1231         return ret;
1232 }
1233
1234 static int zram_remove(struct zram *zram)
1235 {
1236         struct block_device *bdev;
1237
1238         bdev = bdget_disk(zram->disk, 0);
1239         if (!bdev)
1240                 return -ENOMEM;
1241
1242         mutex_lock(&bdev->bd_mutex);
1243         if (bdev->bd_openers || zram->claim) {
1244                 mutex_unlock(&bdev->bd_mutex);
1245                 bdput(bdev);
1246                 return -EBUSY;
1247         }
1248
1249         zram->claim = true;
1250         mutex_unlock(&bdev->bd_mutex);
1251
1252         /*
1253          * Remove sysfs first, so no one will perform a disksize
1254          * store while we destroy the devices. This also helps during
1255          * hot_remove -- zram_reset_device() is the last holder of
1256          * ->init_lock, no later/concurrent disksize_store() or any
1257          * other sysfs handlers are possible.
1258          */
1259         sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
1260                         &zram_disk_attr_group);
1261
1262         /* Make sure all the pending I/O are finished */
1263         fsync_bdev(bdev);
1264         zram_reset_device(zram);
1265         bdput(bdev);
1266
1267         pr_info("Removed device: %s\n", zram->disk->disk_name);
1268
1269         blk_cleanup_queue(zram->disk->queue);
1270         del_gendisk(zram->disk);
1271         put_disk(zram->disk);
1272         kfree(zram);
1273         return 0;
1274 }
1275
1276 /* zram-control sysfs attributes */
1277
1278 /*
1279  * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
1280  * sense that reading from this file does alter the state of your system -- it
1281  * creates a new un-initialized zram device and returns back this device's
1282  * device_id (or an error code if it fails to create a new device).
1283  */
1284 static ssize_t hot_add_show(struct class *class,
1285                         struct class_attribute *attr,
1286                         char *buf)
1287 {
1288         int ret;
1289
1290         mutex_lock(&zram_index_mutex);
1291         ret = zram_add();
1292         mutex_unlock(&zram_index_mutex);
1293
1294         if (ret < 0)
1295                 return ret;
1296         return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
1297 }
1298 static CLASS_ATTR_RO(hot_add);
1299
1300 static ssize_t hot_remove_store(struct class *class,
1301                         struct class_attribute *attr,
1302                         const char *buf,
1303                         size_t count)
1304 {
1305         struct zram *zram;
1306         int ret, dev_id;
1307
1308         /* dev_id is gendisk->first_minor, which is `int' */
1309         ret = kstrtoint(buf, 10, &dev_id);
1310         if (ret)
1311                 return ret;
1312         if (dev_id < 0)
1313                 return -EINVAL;
1314
1315         mutex_lock(&zram_index_mutex);
1316
1317         zram = idr_find(&zram_index_idr, dev_id);
1318         if (zram) {
1319                 ret = zram_remove(zram);
1320                 if (!ret)
1321                         idr_remove(&zram_index_idr, dev_id);
1322         } else {
1323                 ret = -ENODEV;
1324         }
1325
1326         mutex_unlock(&zram_index_mutex);
1327         return ret ? ret : count;
1328 }
1329 static CLASS_ATTR_WO(hot_remove);
1330
1331 static struct attribute *zram_control_class_attrs[] = {
1332         &class_attr_hot_add.attr,
1333         &class_attr_hot_remove.attr,
1334         NULL,
1335 };
1336 ATTRIBUTE_GROUPS(zram_control_class);
1337
1338 static struct class zram_control_class = {
1339         .name           = "zram-control",
1340         .owner          = THIS_MODULE,
1341         .class_groups   = zram_control_class_groups,
1342 };
1343
1344 static int zram_remove_cb(int id, void *ptr, void *data)
1345 {
1346         zram_remove(ptr);
1347         return 0;
1348 }
1349
1350 static void destroy_devices(void)
1351 {
1352         class_unregister(&zram_control_class);
1353         idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
1354         idr_destroy(&zram_index_idr);
1355         unregister_blkdev(zram_major, "zram");
1356         cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
1357 }
1358
1359 static int __init zram_init(void)
1360 {
1361         int ret;
1362
1363         ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
1364                                       zcomp_cpu_up_prepare, zcomp_cpu_dead);
1365         if (ret < 0)
1366                 return ret;
1367
1368         ret = class_register(&zram_control_class);
1369         if (ret) {
1370                 pr_err("Unable to register zram-control class\n");
1371                 cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
1372                 return ret;
1373         }
1374
1375         zram_major = register_blkdev(0, "zram");
1376         if (zram_major <= 0) {
1377                 pr_err("Unable to get major number\n");
1378                 class_unregister(&zram_control_class);
1379                 cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
1380                 return -EBUSY;
1381         }
1382
1383         while (num_devices != 0) {
1384                 mutex_lock(&zram_index_mutex);
1385                 ret = zram_add();
1386                 mutex_unlock(&zram_index_mutex);
1387                 if (ret < 0)
1388                         goto out_error;
1389                 num_devices--;
1390         }
1391
1392         return 0;
1393
1394 out_error:
1395         destroy_devices();
1396         return ret;
1397 }
1398
1399 static void __exit zram_exit(void)
1400 {
1401         destroy_devices();
1402 }
1403
1404 module_init(zram_init);
1405 module_exit(zram_exit);
1406
1407 module_param(num_devices, uint, 0);
1408 MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");
1409
1410 MODULE_LICENSE("Dual BSD/GPL");
1411 MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
1412 MODULE_DESCRIPTION("Compressed RAM Block Device");