mm/zswap.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * zswap.c - zswap driver file
   4  *
   5  * zswap is a backend for frontswap that takes pages that are in the process
   6  * of being swapped out and attempts to compress and store them in a
   7  * RAM-based memory pool.  This can result in a significant I/O reduction on
   8  * the swap device and, in the case where decompressing from RAM is faster
   9  * than reading from the swap device, can also improve workload performance.
  10  *
  11  * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
  12 */
  13
  14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15
  16 #include <linux/module.h>
  17 #include <linux/cpu.h>
  18 #include <linux/highmem.h>
  19 #include <linux/slab.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/types.h>
  22 #include <linux/atomic.h>
  23 #include <linux/frontswap.h>
  24 #include <linux/rbtree.h>
  25 #include <linux/swap.h>
  26 #include <linux/crypto.h>
  27 #include <linux/mempool.h>
  28 #include <linux/zpool.h>
  29
  30 #include <linux/mm_types.h>
  31 #include <linux/page-flags.h>
  32 #include <linux/swapops.h>
  33 #include <linux/writeback.h>
  34 #include <linux/pagemap.h>
  35
  36 /*********************************
  37 * statistics
  38 **********************************/
  39 /* Total bytes used by the compressed storage */
  40 static u64 zswap_pool_total_size;
  41 /* The number of compressed pages currently stored in zswap */
  42 static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
  43 /* The number of same-value filled pages currently stored in zswap */
  44 static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);
  45
  46 /*
  47  * The statistics below are not protected from concurrent access for
  48  * performance reasons so they may not be a 100% accurate.  However,
  49  * they do provide useful information on roughly how many times a
  50  * certain event is occurring.
  51 */
  52
  53 /* Pool limit was hit (see zswap_max_pool_percent) */
  54 static u64 zswap_pool_limit_hit;
  55 /* Pages written back when pool limit was reached */
  56 static u64 zswap_written_back_pages;
  57 /* Store failed due to a reclaim failure after pool limit was reached */
  58 static u64 zswap_reject_reclaim_fail;
  59 /* Compressed page was too big for the allocator to (optimally) store */
  60 static u64 zswap_reject_compress_poor;
  61 /* Store failed because underlying allocator could not get memory */
  62 static u64 zswap_reject_alloc_fail;
  63 /* Store failed because the entry metadata could not be allocated (rare) */
  64 static u64 zswap_reject_kmemcache_fail;
  65 /* Duplicate store was encountered (rare) */
  66 static u64 zswap_duplicate_entry;
  67
  68 /*********************************
  69 * tunables
  70 **********************************/
  71
  72 #define ZSWAP_PARAM_UNSET ""
  73
  74 /* Enable/disable zswap (disabled by default) */
  75 static bool zswap_enabled;
  76 static int zswap_enabled_param_set(const char *,
  77                                    const struct kernel_param *);
  78 static struct kernel_param_ops zswap_enabled_param_ops = {
  79         .set =          zswap_enabled_param_set,
  80         .get =          param_get_bool,
  81 };
  82 module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
  83
  84 /* Crypto compressor to use */
  85 #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
  86 static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
  87 static int zswap_compressor_param_set(const char *,
  88                                       const struct kernel_param *);
  89 static struct kernel_param_ops zswap_compressor_param_ops = {
  90         .set =          zswap_compressor_param_set,
  91         .get =          param_get_charp,
  92         .free =         param_free_charp,
  93 };
  94 module_param_cb(compressor, &zswap_compressor_param_ops,
  95                 &zswap_compressor, 0644);
  96
  97 /* Compressed storage zpool to use */
  98 #define ZSWAP_ZPOOL_DEFAULT "zbud"
  99 static char *zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
 100 static int zswap_zpool_param_set(const char *, const struct kernel_param *);
 101 static struct kernel_param_ops zswap_zpool_param_ops = {
 102         .set =          zswap_zpool_param_set,
 103         .get =          param_get_charp,
 104         .free =         param_free_charp,
 105 };
 106 module_param_cb(zpool, &zswap_zpool_param_ops, &zswap_zpool_type, 0644);
 107
 108 /* The maximum percentage of memory that the compressed pool can occupy */
 109 static unsigned int zswap_max_pool_percent = 20;
 110 module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);
 111
 112 /* Enable/disable handling same-value filled pages (enabled by default) */
 113 static bool zswap_same_filled_pages_enabled = true;
 114 module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
 115                    bool, 0644);
 116
 117 /*********************************
 118 * data structures
 119 **********************************/
 120
 121 struct zswap_pool {
 122         struct zpool *zpool;
 123         struct crypto_comp * __percpu *tfm;
 124         struct kref kref;
 125         struct list_head list;
 126         struct work_struct work;
 127         struct hlist_node node;
 128         char tfm_name[CRYPTO_MAX_ALG_NAME];
 129 };
 130
 131 /*
 132  * struct zswap_entry
 133  *
 134  * This structure contains the metadata for tracking a single compressed
 135  * page within zswap.
 136  *
 137  * rbnode - links the entry into red-black tree for the appropriate swap type
 138  * offset - the swap offset for the entry.  Index into the red-black tree.
 139  * refcount - the number of outstanding reference to the entry. This is needed
 140  *            to protect against premature freeing of the entry by code
 141  *            concurrent calls to load, invalidate, and writeback.  The lock
 142  *            for the zswap_tree structure that contains the entry must
 143  *            be held while changing the refcount.  Since the lock must
 144  *            be held, there is no reason to also make refcount atomic.
 145  * length - the length in bytes of the compressed page data.  Needed during
 146  *          decompression. For a same value filled page length is 0.
 147  * pool - the zswap_pool the entry's data is in
 148  * handle - zpool allocation handle that stores the compressed page data
 149  * value - value of the same-value filled pages which have same content
 150  */
 151 struct zswap_entry {
 152         struct rb_node rbnode;
 153         pgoff_t offset;
 154         int refcount;
 155         unsigned int length;
 156         struct zswap_pool *pool;
 157         union {
 158                 unsigned long handle;
 159                 unsigned long value;
 160         };
 161 };
 162
 163 struct zswap_header {
 164         swp_entry_t swpentry;
 165 };
 166
 167 /*
 168  * The tree lock in the zswap_tree struct protects a few things:
 169  * - the rbtree
 170  * - the refcount field of each entry in the tree
 171  */
 172 struct zswap_tree {
 173         struct rb_root rbroot;
 174         spinlock_t lock;
 175 };
 176
 177 static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
 178
 179 /* RCU-protected iteration */
 180 static LIST_HEAD(zswap_pools);
 181 /* protects zswap_pools list modification */
 182 static DEFINE_SPINLOCK(zswap_pools_lock);
 183 /* pool counter to provide unique names to zpool */
 184 static atomic_t zswap_pools_count = ATOMIC_INIT(0);
 185
 186 /* used by param callback function */
 187 static bool zswap_init_started;
 188
 189 /* fatal error during init */
 190 static bool zswap_init_failed;
 191
 192 /* init completed, but couldn't create the initial pool */
 193 static bool zswap_has_pool;
 194
 195 /*********************************
 196 * helpers and fwd declarations
 197 **********************************/
 198
 199 #define zswap_pool_debug(msg, p)                                \
 200         pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,         \
 201                  zpool_get_type((p)->zpool))
 202
 203 static int zswap_writeback_entry(struct zpool *pool, unsigned long handle);
 204 static int zswap_pool_get(struct zswap_pool *pool);
 205 static void zswap_pool_put(struct zswap_pool *pool);
 206
 207 static const struct zpool_ops zswap_zpool_ops = {
 208         .evict = zswap_writeback_entry
 209 };
 210
 211 static bool zswap_is_full(void)
 212 {
 213         return totalram_pages() * zswap_max_pool_percent / 100 <
 214                         DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
 215 }
 216
 217 static void zswap_update_total_size(void)
 218 {
 219         struct zswap_pool *pool;
 220         u64 total = 0;
 221
 222         rcu_read_lock();
 223
 224         list_for_each_entry_rcu(pool, &zswap_pools, list)
 225                 total += zpool_get_total_size(pool->zpool);
 226
 227         rcu_read_unlock();
 228
 229         zswap_pool_total_size = total;
 230 }
 231
 232 /*********************************
 233 * zswap entry functions
 234 **********************************/
 235 static struct kmem_cache *zswap_entry_cache;
 236
 237 static int __init zswap_entry_cache_create(void)
 238 {
 239         zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
 240         return zswap_entry_cache == NULL;
 241 }
 242
 243 static void __init zswap_entry_cache_destroy(void)
 244 {
 245         kmem_cache_destroy(zswap_entry_cache);
 246 }
 247
 248 static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
 249 {
 250         struct zswap_entry *entry;
 251         entry = kmem_cache_alloc(zswap_entry_cache, gfp);
 252         if (!entry)
 253                 return NULL;
 254         entry->refcount = 1;
 255         RB_CLEAR_NODE(&entry->rbnode);
 256         return entry;
 257 }
 258
 259 static void zswap_entry_cache_free(struct zswap_entry *entry)
 260 {
 261         kmem_cache_free(zswap_entry_cache, entry);
 262 }
 263
 264 /*********************************
 265 * rbtree functions
 266 **********************************/
 267 static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
 268 {
 269         struct rb_node *node = root->rb_node;
 270         struct zswap_entry *entry;
 271
 272         while (node) {
 273                 entry = rb_entry(node, struct zswap_entry, rbnode);
 274                 if (entry->offset > offset)
 275                         node = node->rb_left;
 276                 else if (entry->offset < offset)
 277                         node = node->rb_right;
 278                 else
 279                         return entry;
 280         }
 281         return NULL;
 282 }
 283
 284 /*
 285  * In the case that a entry with the same offset is found, a pointer to
 286  * the existing entry is stored in dupentry and the function returns -EEXIST
 287  */
 288 static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
 289                         struct zswap_entry **dupentry)
 290 {
 291         struct rb_node **link = &root->rb_node, *parent = NULL;
 292         struct zswap_entry *myentry;
 293
 294         while (*link) {
 295                 parent = *link;
 296                 myentry = rb_entry(parent, struct zswap_entry, rbnode);
 297                 if (myentry->offset > entry->offset)
 298                         link = &(*link)->rb_left;
 299                 else if (myentry->offset < entry->offset)
 300                         link = &(*link)->rb_right;
 301                 else {
 302                         *dupentry = myentry;
 303                         return -EEXIST;
 304                 }
 305         }
 306         rb_link_node(&entry->rbnode, parent, link);
 307         rb_insert_color(&entry->rbnode, root);
 308         return 0;
 309 }
 310
 311 static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
 312 {
 313         if (!RB_EMPTY_NODE(&entry->rbnode)) {
 314                 rb_erase(&entry->rbnode, root);
 315                 RB_CLEAR_NODE(&entry->rbnode);
 316         }
 317 }
 318
 319 /*
 320  * Carries out the common pattern of freeing and entry's zpool allocation,
 321  * freeing the entry itself, and decrementing the number of stored pages.
 322  */
 323 static void zswap_free_entry(struct zswap_entry *entry)
 324 {
 325         if (!entry->length)
 326                 atomic_dec(&zswap_same_filled_pages);
 327         else {
 328                 zpool_free(entry->pool->zpool, entry->handle);
 329                 zswap_pool_put(entry->pool);
 330         }
 331         zswap_entry_cache_free(entry);
 332         atomic_dec(&zswap_stored_pages);
 333         zswap_update_total_size();
 334 }
 335
 336 /* caller must hold the tree lock */
 337 static void zswap_entry_get(struct zswap_entry *entry)
 338 {
 339         entry->refcount++;
 340 }
 341
 342 /* caller must hold the tree lock
 343 * remove from the tree and free it, if nobody reference the entry
 344 */
 345 static void zswap_entry_put(struct zswap_tree *tree,
 346                         struct zswap_entry *entry)
 347 {
 348         int refcount = --entry->refcount;
 349
 350         BUG_ON(refcount < 0);
 351         if (refcount == 0) {
 352                 zswap_rb_erase(&tree->rbroot, entry);
 353                 zswap_free_entry(entry);
 354         }
 355 }
 356
 357 /* caller must hold the tree lock */
 358 static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
 359                                 pgoff_t offset)
 360 {
 361         struct zswap_entry *entry;
 362
 363         entry = zswap_rb_search(root, offset);
 364         if (entry)
 365                 zswap_entry_get(entry);
 366
 367         return entry;
 368 }
 369
 370 /*********************************
 371 * per-cpu code
 372 **********************************/
 373 static DEFINE_PER_CPU(u8 *, zswap_dstmem);
 374
 375 static int zswap_dstmem_prepare(unsigned int cpu)
 376 {
 377         u8 *dst;
 378
 379         dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
 380         if (!dst)
 381                 return -ENOMEM;
 382
 383         per_cpu(zswap_dstmem, cpu) = dst;
 384         return 0;
 385 }
 386
 387 static int zswap_dstmem_dead(unsigned int cpu)
 388 {
 389         u8 *dst;
 390
 391         dst = per_cpu(zswap_dstmem, cpu);
 392         kfree(dst);
 393         per_cpu(zswap_dstmem, cpu) = NULL;
 394
 395         return 0;
 396 }
 397
 398 static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 399 {
 400         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
 401         struct crypto_comp *tfm;
 402
 403         if (WARN_ON(*per_cpu_ptr(pool->tfm, cpu)))
 404                 return 0;
 405
 406         tfm = crypto_alloc_comp(pool->tfm_name, 0, 0);
 407         if (IS_ERR_OR_NULL(tfm)) {
 408                 pr_err("could not alloc crypto comp %s : %ld\n",
 409                        pool->tfm_name, PTR_ERR(tfm));
 410                 return -ENOMEM;
 411         }
 412         *per_cpu_ptr(pool->tfm, cpu) = tfm;
 413         return 0;
 414 }
 415
 416 static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
 417 {
 418         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
 419         struct crypto_comp *tfm;
 420
 421         tfm = *per_cpu_ptr(pool->tfm, cpu);
 422         if (!IS_ERR_OR_NULL(tfm))
 423                 crypto_free_comp(tfm);
 424         *per_cpu_ptr(pool->tfm, cpu) = NULL;
 425         return 0;
 426 }
 427
 428 /*********************************
 429 * pool functions
 430 **********************************/
 431
 432 static struct zswap_pool *__zswap_pool_current(void)
 433 {
 434         struct zswap_pool *pool;
 435
 436         pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
 437         WARN_ONCE(!pool && zswap_has_pool,
 438                   "%s: no page storage pool!\n", __func__);
 439
 440         return pool;
 441 }
 442
 443 static struct zswap_pool *zswap_pool_current(void)
 444 {
 445         assert_spin_locked(&zswap_pools_lock);
 446
 447         return __zswap_pool_current();
 448 }
 449
 450 static struct zswap_pool *zswap_pool_current_get(void)
 451 {
 452         struct zswap_pool *pool;
 453
 454         rcu_read_lock();
 455
 456         pool = __zswap_pool_current();
 457         if (!zswap_pool_get(pool))
 458                 pool = NULL;
 459
 460         rcu_read_unlock();
 461
 462         return pool;
 463 }
 464
 465 static struct zswap_pool *zswap_pool_last_get(void)
 466 {
 467         struct zswap_pool *pool, *last = NULL;
 468
 469         rcu_read_lock();
 470
 471         list_for_each_entry_rcu(pool, &zswap_pools, list)
 472                 last = pool;
 473         WARN_ONCE(!last && zswap_has_pool,
 474                   "%s: no page storage pool!\n", __func__);
 475         if (!zswap_pool_get(last))
 476                 last = NULL;
 477
 478         rcu_read_unlock();
 479
 480         return last;
 481 }
 482
 483 /* type and compressor must be null-terminated */
 484 static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
 485 {
 486         struct zswap_pool *pool;
 487
 488         assert_spin_locked(&zswap_pools_lock);
 489
 490         list_for_each_entry_rcu(pool, &zswap_pools, list) {
 491                 if (strcmp(pool->tfm_name, compressor))
 492                         continue;
 493                 if (strcmp(zpool_get_type(pool->zpool), type))
 494                         continue;
 495                 /* if we can't get it, it's about to be destroyed */
 496                 if (!zswap_pool_get(pool))
 497                         continue;
 498                 return pool;
 499         }
 500
 501         return NULL;
 502 }
 503
 504 static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
 505 {
 506         struct zswap_pool *pool;
 507         char name[38]; /* 'zswap' + 32 char (max) num + \0 */
 508         gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
 509         int ret;
 510
 511         if (!zswap_has_pool) {
 512                 /* if either are unset, pool initialization failed, and we
 513                  * need both params to be set correctly before trying to
 514                  * create a pool.
 515                  */
 516                 if (!strcmp(type, ZSWAP_PARAM_UNSET))
 517                         return NULL;
 518                 if (!strcmp(compressor, ZSWAP_PARAM_UNSET))
 519                         return NULL;
 520         }
 521
 522         pool = kzalloc(sizeof(*pool), GFP_KERNEL);
 523         if (!pool)
 524                 return NULL;
 525
 526         /* unique name for each pool specifically required by zsmalloc */
 527         snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));
 528
 529         pool->zpool = zpool_create_pool(type, name, gfp, &zswap_zpool_ops);
 530         if (!pool->zpool) {
 531                 pr_err("%s zpool not available\n", type);
 532                 goto error;
 533         }
 534         pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));
 535
 536         strlcpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
 537         pool->tfm = alloc_percpu(struct crypto_comp *);
 538         if (!pool->tfm) {
 539                 pr_err("percpu alloc failed\n");
 540                 goto error;
 541         }
 542
 543         ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
 544                                        &pool->node);
 545         if (ret)
 546                 goto error;
 547         pr_debug("using %s compressor\n", pool->tfm_name);
 548
 549         /* being the current pool takes 1 ref; this func expects the
 550          * caller to always add the new pool as the current pool
 551          */
 552         kref_init(&pool->kref);
 553         INIT_LIST_HEAD(&pool->list);
 554
 555         zswap_pool_debug("created", pool);
 556
 557         return pool;
 558
 559 error:
 560         free_percpu(pool->tfm);
 561         if (pool->zpool)
 562                 zpool_destroy_pool(pool->zpool);
 563         kfree(pool);
 564         return NULL;
 565 }
 566
 567 static __init struct zswap_pool *__zswap_pool_create_fallback(void)
 568 {
 569         bool has_comp, has_zpool;
 570
 571         has_comp = crypto_has_comp(zswap_compressor, 0, 0);
 572         if (!has_comp && strcmp(zswap_compressor, ZSWAP_COMPRESSOR_DEFAULT)) {
 573                 pr_err("compressor %s not available, using default %s\n",
 574                        zswap_compressor, ZSWAP_COMPRESSOR_DEFAULT);
 575                 param_free_charp(&zswap_compressor);
 576                 zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
 577                 has_comp = crypto_has_comp(zswap_compressor, 0, 0);
 578         }
 579         if (!has_comp) {
 580                 pr_err("default compressor %s not available\n",
 581                        zswap_compressor);
 582                 param_free_charp(&zswap_compressor);
 583                 zswap_compressor = ZSWAP_PARAM_UNSET;
 584         }
 585
 586         has_zpool = zpool_has_pool(zswap_zpool_type);
 587         if (!has_zpool && strcmp(zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT)) {
 588                 pr_err("zpool %s not available, using default %s\n",
 589                        zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT);
 590                 param_free_charp(&zswap_zpool_type);
 591                 zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
 592                 has_zpool = zpool_has_pool(zswap_zpool_type);
 593         }
 594         if (!has_zpool) {
 595                 pr_err("default zpool %s not available\n",
 596                        zswap_zpool_type);
 597                 param_free_charp(&zswap_zpool_type);
 598                 zswap_zpool_type = ZSWAP_PARAM_UNSET;
 599         }
 600
 601         if (!has_comp || !has_zpool)
 602                 return NULL;
 603
 604         return zswap_pool_create(zswap_zpool_type, zswap_compressor);
 605 }
 606
 607 static void zswap_pool_destroy(struct zswap_pool *pool)
 608 {
 609         zswap_pool_debug("destroying", pool);
 610
 611         cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
 612         free_percpu(pool->tfm);
 613         zpool_destroy_pool(pool->zpool);
 614         kfree(pool);
 615 }
 616
 617 static int __must_check zswap_pool_get(struct zswap_pool *pool)
 618 {
 619         if (!pool)
 620                 return 0;
 621
 622         return kref_get_unless_zero(&pool->kref);
 623 }
 624
 625 static void __zswap_pool_release(struct work_struct *work)
 626 {
 627         struct zswap_pool *pool = container_of(work, typeof(*pool), work);
 628
 629         synchronize_rcu();
 630
 631         /* nobody should have been able to get a kref... */
 632         WARN_ON(kref_get_unless_zero(&pool->kref));
 633
 634         /* pool is now off zswap_pools list and has no references. */
 635         zswap_pool_destroy(pool);
 636 }
 637
 638 static void __zswap_pool_empty(struct kref *kref)
 639 {
 640         struct zswap_pool *pool;
 641
 642         pool = container_of(kref, typeof(*pool), kref);
 643
 644         spin_lock(&zswap_pools_lock);
 645
 646         WARN_ON(pool == zswap_pool_current());
 647
 648         list_del_rcu(&pool->list);
 649
 650         INIT_WORK(&pool->work, __zswap_pool_release);
 651         schedule_work(&pool->work);
 652
 653         spin_unlock(&zswap_pools_lock);
 654 }
 655
 656 static void zswap_pool_put(struct zswap_pool *pool)
 657 {
 658         kref_put(&pool->kref, __zswap_pool_empty);
 659 }
 660
 661 /*********************************
 662 * param callbacks
 663 **********************************/
 664
 665 /* val must be a null-terminated string */
 666 static int __zswap_param_set(const char *val, const struct kernel_param *kp,
 667                              char *type, char *compressor)
 668 {
 669         struct zswap_pool *pool, *put_pool = NULL;
 670         char *s = strstrip((char *)val);
 671         int ret;
 672
 673         if (zswap_init_failed) {
 674                 pr_err("can't set param, initialization failed\n");
 675                 return -ENODEV;
 676         }
 677
 678         /* no change required */
 679         if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
 680                 return 0;
 681
 682         /* if this is load-time (pre-init) param setting,
 683          * don't create a pool; that's done during init.
 684          */
 685         if (!zswap_init_started)
 686                 return param_set_charp(s, kp);
 687
 688         if (!type) {
 689                 if (!zpool_has_pool(s)) {
 690                         pr_err("zpool %s not available\n", s);
 691                         return -ENOENT;
 692                 }
 693                 type = s;
 694         } else if (!compressor) {
 695                 if (!crypto_has_comp(s, 0, 0)) {
 696                         pr_err("compressor %s not available\n", s);
 697                         return -ENOENT;
 698                 }
 699                 compressor = s;
 700         } else {
 701                 WARN_ON(1);
 702                 return -EINVAL;
 703         }
 704
 705         spin_lock(&zswap_pools_lock);
 706
 707         pool = zswap_pool_find_get(type, compressor);
 708         if (pool) {
 709                 zswap_pool_debug("using existing", pool);
 710                 WARN_ON(pool == zswap_pool_current());
 711                 list_del_rcu(&pool->list);
 712         }
 713
 714         spin_unlock(&zswap_pools_lock);
 715
 716         if (!pool)
 717                 pool = zswap_pool_create(type, compressor);
 718
 719         if (pool)
 720                 ret = param_set_charp(s, kp);
 721         else
 722                 ret = -EINVAL;
 723
 724         spin_lock(&zswap_pools_lock);
 725
 726         if (!ret) {
 727                 put_pool = zswap_pool_current();
 728                 list_add_rcu(&pool->list, &zswap_pools);
 729                 zswap_has_pool = true;
 730         } else if (pool) {
 731                 /* add the possibly pre-existing pool to the end of the pools
 732                  * list; if it's new (and empty) then it'll be removed and
 733                  * destroyed by the put after we drop the lock
 734                  */
 735                 list_add_tail_rcu(&pool->list, &zswap_pools);
 736                 put_pool = pool;
 737         }
 738
 739         spin_unlock(&zswap_pools_lock);
 740
 741         if (!zswap_has_pool && !pool) {
 742                 /* if initial pool creation failed, and this pool creation also
 743                  * failed, maybe both compressor and zpool params were bad.
 744                  * Allow changing this param, so pool creation will succeed
 745                  * when the other param is changed. We already verified this
 746                  * param is ok in the zpool_has_pool() or crypto_has_comp()
 747                  * checks above.
 748                  */
 749                 ret = param_set_charp(s, kp);
 750         }
 751
 752         /* drop the ref from either the old current pool,
 753          * or the new pool we failed to add
 754          */
 755         if (put_pool)
 756                 zswap_pool_put(put_pool);
 757
 758         return ret;
 759 }
 760
 761 static int zswap_compressor_param_set(const char *val,
 762                                       const struct kernel_param *kp)
 763 {
 764         return __zswap_param_set(val, kp, zswap_zpool_type, NULL);
 765 }
 766
 767 static int zswap_zpool_param_set(const char *val,
 768                                  const struct kernel_param *kp)
 769 {
 770         return __zswap_param_set(val, kp, NULL, zswap_compressor);
 771 }
 772
 773 static int zswap_enabled_param_set(const char *val,
 774                                    const struct kernel_param *kp)
 775 {
 776         if (zswap_init_failed) {
 777                 pr_err("can't enable, initialization failed\n");
 778                 return -ENODEV;
 779         }
 780         if (!zswap_has_pool && zswap_init_started) {
 781                 pr_err("can't enable, no pool configured\n");
 782                 return -ENODEV;
 783         }
 784
 785         return param_set_bool(val, kp);
 786 }
 787
 788 /*********************************
 789 * writeback code
 790 **********************************/
 791 /* return enum for zswap_get_swap_cache_page */
 792 enum zswap_get_swap_ret {
 793         ZSWAP_SWAPCACHE_NEW,
 794         ZSWAP_SWAPCACHE_EXIST,
 795         ZSWAP_SWAPCACHE_FAIL,
 796 };
 797
 798 /*
 799  * zswap_get_swap_cache_page
 800  *
 801  * This is an adaption of read_swap_cache_async()
 802  *
 803  * This function tries to find a page with the given swap entry
 804  * in the swapper_space address space (the swap cache).  If the page
 805  * is found, it is returned in retpage.  Otherwise, a page is allocated,
 806  * added to the swap cache, and returned in retpage.
 807  *
 808  * If success, the swap cache page is returned in retpage
 809  * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
 810  * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
 811  *     the new page is added to swapcache and locked
 812  * Returns ZSWAP_SWAPCACHE_FAIL on error
 813  */
 814 static int zswap_get_swap_cache_page(swp_entry_t entry,
 815                                 struct page **retpage)
 816 {
 817         bool page_was_allocated;
 818
 819         *retpage = __read_swap_cache_async(entry, GFP_KERNEL,
 820                         NULL, 0, &page_was_allocated);
 821         if (page_was_allocated)
 822                 return ZSWAP_SWAPCACHE_NEW;
 823         if (!*retpage)
 824                 return ZSWAP_SWAPCACHE_FAIL;
 825         return ZSWAP_SWAPCACHE_EXIST;
 826 }
 827
 828 /*
 829  * Attempts to free an entry by adding a page to the swap cache,
 830  * decompressing the entry data into the page, and issuing a
 831  * bio write to write the page back to the swap device.
 832  *
 833  * This can be thought of as a "resumed writeback" of the page
 834  * to the swap device.  We are basically resuming the same swap
 835  * writeback path that was intercepted with the frontswap_store()
 836  * in the first place.  After the page has been decompressed into
 837  * the swap cache, the compressed version stored by zswap can be
 838  * freed.
 839  */
 840 static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 841 {
 842         struct zswap_header *zhdr;
 843         swp_entry_t swpentry;
 844         struct zswap_tree *tree;
 845         pgoff_t offset;
 846         struct zswap_entry *entry;
 847         struct page *page;
 848         struct crypto_comp *tfm;
 849         u8 *src, *dst;
 850         unsigned int dlen;
 851         int ret;
 852         struct writeback_control wbc = {
 853                 .sync_mode = WB_SYNC_NONE,
 854         };
 855
 856         /* extract swpentry from data */
 857         zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
 858         swpentry = zhdr->swpentry; /* here */
 859         tree = zswap_trees[swp_type(swpentry)];
 860         offset = swp_offset(swpentry);
 861
 862         /* find and ref zswap entry */
 863         spin_lock(&tree->lock);
 864         entry = zswap_entry_find_get(&tree->rbroot, offset);
 865         if (!entry) {
 866                 /* entry was invalidated */
 867                 spin_unlock(&tree->lock);
 868                 zpool_unmap_handle(pool, handle);
 869                 return 0;
 870         }
 871         spin_unlock(&tree->lock);
 872         BUG_ON(offset != entry->offset);
 873
 874         /* try to allocate swap cache page */
 875         switch (zswap_get_swap_cache_page(swpentry, &page)) {
 876         case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
 877                 ret = -ENOMEM;
 878                 goto fail;
 879
 880         case ZSWAP_SWAPCACHE_EXIST:
 881                 /* page is already in the swap cache, ignore for now */
 882                 put_page(page);
 883                 ret = -EEXIST;
 884                 goto fail;
 885
 886         case ZSWAP_SWAPCACHE_NEW: /* page is locked */
 887                 /* decompress */
 888                 dlen = PAGE_SIZE;
 889                 src = (u8 *)zhdr + sizeof(struct zswap_header);
 890                 dst = kmap_atomic(page);
 891                 tfm = *get_cpu_ptr(entry->pool->tfm);
 892                 ret = crypto_comp_decompress(tfm, src, entry->length,
 893                                              dst, &dlen);
 894                 put_cpu_ptr(entry->pool->tfm);
 895                 kunmap_atomic(dst);
 896                 BUG_ON(ret);
 897                 BUG_ON(dlen != PAGE_SIZE);
 898
 899                 /* page is up to date */
 900                 SetPageUptodate(page);
 901         }
 902
 903         /* move it to the tail of the inactive list after end_writeback */
 904         SetPageReclaim(page);
 905
 906         /* start writeback */
 907         __swap_writepage(page, &wbc, end_swap_bio_write);
 908         put_page(page);
 909         zswap_written_back_pages++;
 910
 911         spin_lock(&tree->lock);
 912         /* drop local reference */
 913         zswap_entry_put(tree, entry);
 914
 915         /*
 916         * There are two possible situations for entry here:
 917         * (1) refcount is 1(normal case),  entry is valid and on the tree
 918         * (2) refcount is 0, entry is freed and not on the tree
 919         *     because invalidate happened during writeback
 920         *  search the tree and free the entry if find entry
 921         */
 922         if (entry == zswap_rb_search(&tree->rbroot, offset))
 923                 zswap_entry_put(tree, entry);
 924         spin_unlock(&tree->lock);
 925
 926         goto end;
 927
 928         /*
 929         * if we get here due to ZSWAP_SWAPCACHE_EXIST
 930         * a load may happening concurrently
 931         * it is safe and okay to not free the entry
 932         * if we free the entry in the following put
 933         * it it either okay to return !0
 934         */
 935 fail:
 936         spin_lock(&tree->lock);
 937         zswap_entry_put(tree, entry);
 938         spin_unlock(&tree->lock);
 939
 940 end:
 941         zpool_unmap_handle(pool, handle);
 942         return ret;
 943 }
 944
 945 static int zswap_shrink(void)
 946 {
 947         struct zswap_pool *pool;
 948         int ret;
 949
 950         pool = zswap_pool_last_get();
 951         if (!pool)
 952                 return -ENOENT;
 953
 954         ret = zpool_shrink(pool->zpool, 1, NULL);
 955
 956         zswap_pool_put(pool);
 957
 958         return ret;
 959 }
 960
 961 static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
 962 {
 963         unsigned int pos;
 964         unsigned long *page;
 965
 966         page = (unsigned long *)ptr;
 967         for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
 968                 if (page[pos] != page[0])
 969                         return 0;
 970         }
 971         *value = page[0];
 972         return 1;
 973 }
 974
 975 static void zswap_fill_page(void *ptr, unsigned long value)
 976 {
 977         unsigned long *page;
 978
 979         page = (unsigned long *)ptr;
 980         memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
 981 }
 982
 983 /*********************************
 984 * frontswap hooks
 985 **********************************/
 986 /* attempts to compress and store an single page */
 987 static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 988                                 struct page *page)
 989 {
 990         struct zswap_tree *tree = zswap_trees[type];
 991         struct zswap_entry *entry, *dupentry;
 992         struct crypto_comp *tfm;
 993         int ret;
 994         unsigned int hlen, dlen = PAGE_SIZE;
 995         unsigned long handle, value;
 996         char *buf;
 997         u8 *src, *dst;
 998         struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) };
 999         gfp_t gfp;
1000
1001         /* THP isn't supported */
1002         if (PageTransHuge(page)) {
1003                 ret = -EINVAL;
1004                 goto reject;
1005         }
1006
1007         if (!zswap_enabled || !tree) {
1008                 ret = -ENODEV;
1009                 goto reject;
1010         }
1011
1012         /* reclaim space if needed */
1013         if (zswap_is_full()) {
1014                 zswap_pool_limit_hit++;
1015                 if (zswap_shrink()) {
1016                         zswap_reject_reclaim_fail++;
1017                         ret = -ENOMEM;
1018                         goto reject;
1019                 }
1020
1021                 /* A second zswap_is_full() check after
1022                  * zswap_shrink() to make sure it's now
1023                  * under the max_pool_percent
1024                  */
1025                 if (zswap_is_full()) {
1026                         ret = -ENOMEM;
1027                         goto reject;
1028                 }
1029         }
1030
1031         /* allocate entry */
1032         entry = zswap_entry_cache_alloc(GFP_KERNEL);
1033         if (!entry) {
1034                 zswap_reject_kmemcache_fail++;
1035                 ret = -ENOMEM;
1036                 goto reject;
1037         }
1038
1039         if (zswap_same_filled_pages_enabled) {
1040                 src = kmap_atomic(page);
1041                 if (zswap_is_page_same_filled(src, &value)) {
1042                         kunmap_atomic(src);
1043                         entry->offset = offset;
1044                         entry->length = 0;
1045                         entry->value = value;
1046                         atomic_inc(&zswap_same_filled_pages);
1047                         goto insert_entry;
1048                 }
1049                 kunmap_atomic(src);
1050         }
1051
1052         /* if entry is successfully added, it keeps the reference */
1053         entry->pool = zswap_pool_current_get();
1054         if (!entry->pool) {
1055                 ret = -EINVAL;
1056                 goto freepage;
1057         }
1058
1059         /* compress */
1060         dst = get_cpu_var(zswap_dstmem);
1061         tfm = *get_cpu_ptr(entry->pool->tfm);
1062         src = kmap_atomic(page);
1063         ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen);
1064         kunmap_atomic(src);
1065         put_cpu_ptr(entry->pool->tfm);
1066         if (ret) {
1067                 ret = -EINVAL;
1068                 goto put_dstmem;
1069         }
1070
1071         /* store */
1072         hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
1073         gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
1074         if (zpool_malloc_support_movable(entry->pool->zpool))
1075                 gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
1076         ret = zpool_malloc(entry->pool->zpool, hlen + dlen, gfp, &handle);
1077         if (ret == -ENOSPC) {
1078                 zswap_reject_compress_poor++;
1079                 goto put_dstmem;
1080         }
1081         if (ret) {
1082                 zswap_reject_alloc_fail++;
1083                 goto put_dstmem;
1084         }
1085         buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_RW);
1086         memcpy(buf, &zhdr, hlen);
1087         memcpy(buf + hlen, dst, dlen);
1088         zpool_unmap_handle(entry->pool->zpool, handle);
1089         put_cpu_var(zswap_dstmem);
1090
1091         /* populate entry */
1092         entry->offset = offset;
1093         entry->handle = handle;
1094         entry->length = dlen;
1095
1096 insert_entry:
1097         /* map */
1098         spin_lock(&tree->lock);
1099         do {
1100                 ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
1101                 if (ret == -EEXIST) {
1102                         zswap_duplicate_entry++;
1103                         /* remove from rbtree */
1104                         zswap_rb_erase(&tree->rbroot, dupentry);
1105                         zswap_entry_put(tree, dupentry);
1106                 }
1107         } while (ret == -EEXIST);
1108         spin_unlock(&tree->lock);
1109
1110         /* update stats */
1111         atomic_inc(&zswap_stored_pages);
1112         zswap_update_total_size();
1113
1114         return 0;
1115
1116 put_dstmem:
1117         put_cpu_var(zswap_dstmem);
1118         zswap_pool_put(entry->pool);
1119 freepage:
1120         zswap_entry_cache_free(entry);
1121 reject:
1122         return ret;
1123 }
1124
1125 /*
1126  * returns 0 if the page was successfully decompressed
1127  * return -1 on entry not found or error
1128 */
1129 static int zswap_frontswap_load(unsigned type, pgoff_t offset,
1130                                 struct page *page)
1131 {
1132         struct zswap_tree *tree = zswap_trees[type];
1133         struct zswap_entry *entry;
1134         struct crypto_comp *tfm;
1135         u8 *src, *dst;
1136         unsigned int dlen;
1137         int ret;
1138
1139         /* find */
1140         spin_lock(&tree->lock);
1141         entry = zswap_entry_find_get(&tree->rbroot, offset);
1142         if (!entry) {
1143                 /* entry was written back */
1144                 spin_unlock(&tree->lock);
1145                 return -1;
1146         }
1147         spin_unlock(&tree->lock);
1148
1149         if (!entry->length) {
1150                 dst = kmap_atomic(page);
1151                 zswap_fill_page(dst, entry->value);
1152                 kunmap_atomic(dst);
1153                 goto freeentry;
1154         }
1155
1156         /* decompress */
1157         dlen = PAGE_SIZE;
1158         src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
1159         if (zpool_evictable(entry->pool->zpool))
1160                 src += sizeof(struct zswap_header);
1161         dst = kmap_atomic(page);
1162         tfm = *get_cpu_ptr(entry->pool->tfm);
1163         ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen);
1164         put_cpu_ptr(entry->pool->tfm);
1165         kunmap_atomic(dst);
1166         zpool_unmap_handle(entry->pool->zpool, entry->handle);
1167         BUG_ON(ret);
1168
1169 freeentry:
1170         spin_lock(&tree->lock);
1171         zswap_entry_put(tree, entry);
1172         spin_unlock(&tree->lock);
1173
1174         return 0;
1175 }
1176
1177 /* frees an entry in zswap */
1178 static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
1179 {
1180         struct zswap_tree *tree = zswap_trees[type];
1181         struct zswap_entry *entry;
1182
1183         /* find */
1184         spin_lock(&tree->lock);
1185         entry = zswap_rb_search(&tree->rbroot, offset);
1186         if (!entry) {
1187                 /* entry was written back */
1188                 spin_unlock(&tree->lock);
1189                 return;
1190         }
1191
1192         /* remove from rbtree */
1193         zswap_rb_erase(&tree->rbroot, entry);
1194
1195         /* drop the initial reference from entry creation */
1196         zswap_entry_put(tree, entry);
1197
1198         spin_unlock(&tree->lock);
1199 }
1200
1201 /* frees all zswap entries for the given swap type */
1202 static void zswap_frontswap_invalidate_area(unsigned type)
1203 {
1204         struct zswap_tree *tree = zswap_trees[type];
1205         struct zswap_entry *entry, *n;
1206
1207         if (!tree)
1208                 return;
1209
1210         /* walk the tree and free everything */
1211         spin_lock(&tree->lock);
1212         rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
1213                 zswap_free_entry(entry);
1214         tree->rbroot = RB_ROOT;
1215         spin_unlock(&tree->lock);
1216         kfree(tree);
1217         zswap_trees[type] = NULL;
1218 }
1219
1220 static void zswap_frontswap_init(unsigned type)
1221 {
1222         struct zswap_tree *tree;
1223
1224         tree = kzalloc(sizeof(*tree), GFP_KERNEL);
1225         if (!tree) {
1226                 pr_err("alloc failed, zswap disabled for swap type %d\n", type);
1227                 return;
1228         }
1229
1230         tree->rbroot = RB_ROOT;
1231         spin_lock_init(&tree->lock);
1232         zswap_trees[type] = tree;
1233 }
1234
1235 static struct frontswap_ops zswap_frontswap_ops = {
1236         .store = zswap_frontswap_store,
1237         .load = zswap_frontswap_load,
1238         .invalidate_page = zswap_frontswap_invalidate_page,
1239         .invalidate_area = zswap_frontswap_invalidate_area,
1240         .init = zswap_frontswap_init
1241 };
1242
1243 /*********************************
1244 * debugfs functions
1245 **********************************/
1246 #ifdef CONFIG_DEBUG_FS
1247 #include <linux/debugfs.h>
1248
1249 static struct dentry *zswap_debugfs_root;
1250
1251 static int __init zswap_debugfs_init(void)
1252 {
1253         if (!debugfs_initialized())
1254                 return -ENODEV;
1255
1256         zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
1257
1258         debugfs_create_u64("pool_limit_hit", 0444,
1259                            zswap_debugfs_root, &zswap_pool_limit_hit);
1260         debugfs_create_u64("reject_reclaim_fail", 0444,
1261                            zswap_debugfs_root, &zswap_reject_reclaim_fail);
1262         debugfs_create_u64("reject_alloc_fail", 0444,
1263                            zswap_debugfs_root, &zswap_reject_alloc_fail);
1264         debugfs_create_u64("reject_kmemcache_fail", 0444,
1265                            zswap_debugfs_root, &zswap_reject_kmemcache_fail);
1266         debugfs_create_u64("reject_compress_poor", 0444,
1267                            zswap_debugfs_root, &zswap_reject_compress_poor);
1268         debugfs_create_u64("written_back_pages", 0444,
1269                            zswap_debugfs_root, &zswap_written_back_pages);
1270         debugfs_create_u64("duplicate_entry", 0444,
1271                            zswap_debugfs_root, &zswap_duplicate_entry);
1272         debugfs_create_u64("pool_total_size", 0444,
1273                            zswap_debugfs_root, &zswap_pool_total_size);
1274         debugfs_create_atomic_t("stored_pages", 0444,
1275                                 zswap_debugfs_root, &zswap_stored_pages);
1276         debugfs_create_atomic_t("same_filled_pages", 0444,
1277                                 zswap_debugfs_root, &zswap_same_filled_pages);
1278
1279         return 0;
1280 }
1281
1282 static void __exit zswap_debugfs_exit(void)
1283 {
1284         debugfs_remove_recursive(zswap_debugfs_root);
1285 }
1286 #else
1287 static int __init zswap_debugfs_init(void)
1288 {
1289         return 0;
1290 }
1291
1292 static void __exit zswap_debugfs_exit(void) { }
1293 #endif
1294
1295 /*********************************
1296 * module init and exit
1297 **********************************/
1298 static int __init init_zswap(void)
1299 {
1300         struct zswap_pool *pool;
1301         int ret;
1302
1303         zswap_init_started = true;
1304
1305         if (zswap_entry_cache_create()) {
1306                 pr_err("entry cache creation failed\n");
1307                 goto cache_fail;
1308         }
1309
1310         ret = cpuhp_setup_state(CPUHP_MM_ZSWP_MEM_PREPARE, "mm/zswap:prepare",
1311                                 zswap_dstmem_prepare, zswap_dstmem_dead);
1312         if (ret) {
1313                 pr_err("dstmem alloc failed\n");
1314                 goto dstmem_fail;
1315         }
1316
1317         ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
1318                                       "mm/zswap_pool:prepare",
1319                                       zswap_cpu_comp_prepare,
1320                                       zswap_cpu_comp_dead);
1321         if (ret)
1322                 goto hp_fail;
1323
1324         pool = __zswap_pool_create_fallback();
1325         if (pool) {
1326                 pr_info("loaded using pool %s/%s\n", pool->tfm_name,
1327                         zpool_get_type(pool->zpool));
1328                 list_add(&pool->list, &zswap_pools);
1329                 zswap_has_pool = true;
1330         } else {
1331                 pr_err("pool creation failed\n");
1332                 zswap_enabled = false;
1333         }
1334
1335         frontswap_register_ops(&zswap_frontswap_ops);
1336         if (zswap_debugfs_init())
1337                 pr_warn("debugfs initialization failed\n");
1338         return 0;
1339
1340 hp_fail:
1341         cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
1342 dstmem_fail:
1343         zswap_entry_cache_destroy();
1344 cache_fail:
1345         /* if built-in, we aren't unloaded on failure; don't allow use */
1346         zswap_init_failed = true;
1347         zswap_enabled = false;
1348         return -ENOMEM;
1349 }
1350 /* must be late so crypto has time to come up */
1351 late_initcall(init_zswap);
1352
1353 MODULE_LICENSE("GPL");
1354 MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
1355 MODULE_DESCRIPTION("Compressed cache for swap pages");