mm/zswap.c

   1 /*
   2  * zswap.c - zswap driver file
   3  *
   4  * zswap is a backend for frontswap that takes pages that are in the process
   5  * of being swapped out and attempts to compress and store them in a
   6  * RAM-based memory pool.  This can result in a significant I/O reduction on
   7  * the swap device and, in the case where decompressing from RAM is faster
   8  * than reading from the swap device, can also improve workload performance.
   9  *
  10  * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21 */
  22
  23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  24
  25 #include <linux/module.h>
  26 #include <linux/cpu.h>
  27 #include <linux/highmem.h>
  28 #include <linux/slab.h>
  29 #include <linux/spinlock.h>
  30 #include <linux/types.h>
  31 #include <linux/atomic.h>
  32 #include <linux/frontswap.h>
  33 #include <linux/rbtree.h>
  34 #include <linux/swap.h>
  35 #include <linux/crypto.h>
  36 #include <linux/mempool.h>
  37 #include <linux/zbud.h>
  38
  39 #include <linux/mm_types.h>
  40 #include <linux/page-flags.h>
  41 #include <linux/swapops.h>
  42 #include <linux/writeback.h>
  43 #include <linux/pagemap.h>
  44
  45 /*********************************
  46 * statistics
  47 **********************************/
  48 /* Number of memory pages used by the compressed pool */
  49 static u64 zswap_pool_pages;
  50 /* The number of compressed pages currently stored in zswap */
  51 static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
  52
  53 /*
  54  * The statistics below are not protected from concurrent access for
  55  * performance reasons so they may not be a 100% accurate.  However,
  56  * they do provide useful information on roughly how many times a
  57  * certain event is occurring.
  58 */
  59
  60 /* Pool limit was hit (see zswap_max_pool_percent) */
  61 static u64 zswap_pool_limit_hit;
  62 /* Pages written back when pool limit was reached */
  63 static u64 zswap_written_back_pages;
  64 /* Store failed due to a reclaim failure after pool limit was reached */
  65 static u64 zswap_reject_reclaim_fail;
  66 /* Compressed page was too big for the allocator to (optimally) store */
  67 static u64 zswap_reject_compress_poor;
  68 /* Store failed because underlying allocator could not get memory */
  69 static u64 zswap_reject_alloc_fail;
  70 /* Store failed because the entry metadata could not be allocated (rare) */
  71 static u64 zswap_reject_kmemcache_fail;
  72 /* Duplicate store was encountered (rare) */
  73 static u64 zswap_duplicate_entry;
  74
  75 /*********************************
  76 * tunables
  77 **********************************/
  78 /* Enable/disable zswap (disabled by default, fixed at boot for now) */
  79 static bool zswap_enabled __read_mostly;
  80 module_param_named(enabled, zswap_enabled, bool, 0);
  81
  82 /* Compressor to be used by zswap (fixed at boot for now) */
  83 #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
  84 static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
  85 module_param_named(compressor, zswap_compressor, charp, 0);
  86
  87 /* The maximum percentage of memory that the compressed pool can occupy */
  88 static unsigned int zswap_max_pool_percent = 20;
  89 module_param_named(max_pool_percent,
  90                         zswap_max_pool_percent, uint, 0644);
  91
  92 /*********************************
  93 * compression functions
  94 **********************************/
  95 /* per-cpu compression transforms */
  96 static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
  97
  98 enum comp_op {
  99         ZSWAP_COMPOP_COMPRESS,
 100         ZSWAP_COMPOP_DECOMPRESS
 101 };
 102
 103 static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
 104                                 u8 *dst, unsigned int *dlen)
 105 {
 106         struct crypto_comp *tfm;
 107         int ret;
 108
 109         tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
 110         switch (op) {
 111         case ZSWAP_COMPOP_COMPRESS:
 112                 ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
 113                 break;
 114         case ZSWAP_COMPOP_DECOMPRESS:
 115                 ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
 116                 break;
 117         default:
 118                 ret = -EINVAL;
 119         }
 120
 121         put_cpu();
 122         return ret;
 123 }
 124
 125 static int __init zswap_comp_init(void)
 126 {
 127         if (!crypto_has_comp(zswap_compressor, 0, 0)) {
 128                 pr_info("%s compressor not available\n", zswap_compressor);
 129                 /* fall back to default compressor */
 130                 zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
 131                 if (!crypto_has_comp(zswap_compressor, 0, 0))
 132                         /* can't even load the default compressor */
 133                         return -ENODEV;
 134         }
 135         pr_info("using %s compressor\n", zswap_compressor);
 136
 137         /* alloc percpu transforms */
 138         zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
 139         if (!zswap_comp_pcpu_tfms)
 140                 return -ENOMEM;
 141         return 0;
 142 }
 143
 144 static void zswap_comp_exit(void)
 145 {
 146         /* free percpu transforms */
 147         if (zswap_comp_pcpu_tfms)
 148                 free_percpu(zswap_comp_pcpu_tfms);
 149 }
 150
 151 /*********************************
 152 * data structures
 153 **********************************/
 154 /*
 155  * struct zswap_entry
 156  *
 157  * This structure contains the metadata for tracking a single compressed
 158  * page within zswap.
 159  *
 160  * rbnode - links the entry into red-black tree for the appropriate swap type
 161  * refcount - the number of outstanding reference to the entry. This is needed
 162  *            to protect against premature freeing of the entry by code
 163  *            concurent calls to load, invalidate, and writeback.  The lock
 164  *            for the zswap_tree structure that contains the entry must
 165  *            be held while changing the refcount.  Since the lock must
 166  *            be held, there is no reason to also make refcount atomic.
 167  * offset - the swap offset for the entry.  Index into the red-black tree.
 168  * handle - zsmalloc allocation handle that stores the compressed page data
 169  * length - the length in bytes of the compressed page data.  Needed during
 170  *           decompression
 171  */
 172 struct zswap_entry {
 173         struct rb_node rbnode;
 174         pgoff_t offset;
 175         int refcount;
 176         unsigned int length;
 177         unsigned long handle;
 178 };
 179
 180 struct zswap_header {
 181         swp_entry_t swpentry;
 182 };
 183
 184 /*
 185  * The tree lock in the zswap_tree struct protects a few things:
 186  * - the rbtree
 187  * - the refcount field of each entry in the tree
 188  */
 189 struct zswap_tree {
 190         struct rb_root rbroot;
 191         spinlock_t lock;
 192         struct zbud_pool *pool;
 193 };
 194
 195 static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
 196
 197 /*********************************
 198 * zswap entry functions
 199 **********************************/
 200 static struct kmem_cache *zswap_entry_cache;
 201
 202 static int zswap_entry_cache_create(void)
 203 {
 204         zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
 205         return (zswap_entry_cache == NULL);
 206 }
 207
 208 static void zswap_entry_cache_destory(void)
 209 {
 210         kmem_cache_destroy(zswap_entry_cache);
 211 }
 212
 213 static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
 214 {
 215         struct zswap_entry *entry;
 216         entry = kmem_cache_alloc(zswap_entry_cache, gfp);
 217         if (!entry)
 218                 return NULL;
 219         entry->refcount = 1;
 220         return entry;
 221 }
 222
 223 static void zswap_entry_cache_free(struct zswap_entry *entry)
 224 {
 225         kmem_cache_free(zswap_entry_cache, entry);
 226 }
 227
 228 /* caller must hold the tree lock */
 229 static void zswap_entry_get(struct zswap_entry *entry)
 230 {
 231         entry->refcount++;
 232 }
 233
 234 /* caller must hold the tree lock */
 235 static int zswap_entry_put(struct zswap_entry *entry)
 236 {
 237         entry->refcount--;
 238         return entry->refcount;
 239 }
 240
 241 /*********************************
 242 * rbtree functions
 243 **********************************/
 244 static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
 245 {
 246         struct rb_node *node = root->rb_node;
 247         struct zswap_entry *entry;
 248
 249         while (node) {
 250                 entry = rb_entry(node, struct zswap_entry, rbnode);
 251                 if (entry->offset > offset)
 252                         node = node->rb_left;
 253                 else if (entry->offset < offset)
 254                         node = node->rb_right;
 255                 else
 256                         return entry;
 257         }
 258         return NULL;
 259 }
 260
 261 /*
 262  * In the case that a entry with the same offset is found, a pointer to
 263  * the existing entry is stored in dupentry and the function returns -EEXIST
 264  */
 265 static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
 266                         struct zswap_entry **dupentry)
 267 {
 268         struct rb_node **link = &root->rb_node, *parent = NULL;
 269         struct zswap_entry *myentry;
 270
 271         while (*link) {
 272                 parent = *link;
 273                 myentry = rb_entry(parent, struct zswap_entry, rbnode);
 274                 if (myentry->offset > entry->offset)
 275                         link = &(*link)->rb_left;
 276                 else if (myentry->offset < entry->offset)
 277                         link = &(*link)->rb_right;
 278                 else {
 279                         *dupentry = myentry;
 280                         return -EEXIST;
 281                 }
 282         }
 283         rb_link_node(&entry->rbnode, parent, link);
 284         rb_insert_color(&entry->rbnode, root);
 285         return 0;
 286 }
 287
 288 /*********************************
 289 * per-cpu code
 290 **********************************/
 291 static DEFINE_PER_CPU(u8 *, zswap_dstmem);
 292
 293 static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
 294 {
 295         struct crypto_comp *tfm;
 296         u8 *dst;
 297
 298         switch (action) {
 299         case CPU_UP_PREPARE:
 300                 tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
 301                 if (IS_ERR(tfm)) {
 302                         pr_err("can't allocate compressor transform\n");
 303                         return NOTIFY_BAD;
 304                 }
 305                 *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
 306                 dst = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
 307                 if (!dst) {
 308                         pr_err("can't allocate compressor buffer\n");
 309                         crypto_free_comp(tfm);
 310                         *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
 311                         return NOTIFY_BAD;
 312                 }
 313                 per_cpu(zswap_dstmem, cpu) = dst;
 314                 break;
 315         case CPU_DEAD:
 316         case CPU_UP_CANCELED:
 317                 tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
 318                 if (tfm) {
 319                         crypto_free_comp(tfm);
 320                         *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
 321                 }
 322                 dst = per_cpu(zswap_dstmem, cpu);
 323                 kfree(dst);
 324                 per_cpu(zswap_dstmem, cpu) = NULL;
 325                 break;
 326         default:
 327                 break;
 328         }
 329         return NOTIFY_OK;
 330 }
 331
 332 static int zswap_cpu_notifier(struct notifier_block *nb,
 333                                 unsigned long action, void *pcpu)
 334 {
 335         unsigned long cpu = (unsigned long)pcpu;
 336         return __zswap_cpu_notifier(action, cpu);
 337 }
 338
 339 static struct notifier_block zswap_cpu_notifier_block = {
 340         .notifier_call = zswap_cpu_notifier
 341 };
 342
 343 static int zswap_cpu_init(void)
 344 {
 345         unsigned long cpu;
 346
 347         get_online_cpus();
 348         for_each_online_cpu(cpu)
 349                 if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
 350                         goto cleanup;
 351         register_cpu_notifier(&zswap_cpu_notifier_block);
 352         put_online_cpus();
 353         return 0;
 354
 355 cleanup:
 356         for_each_online_cpu(cpu)
 357                 __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
 358         put_online_cpus();
 359         return -ENOMEM;
 360 }
 361
 362 /*********************************
 363 * helpers
 364 **********************************/
 365 static bool zswap_is_full(void)
 366 {
 367         return (totalram_pages * zswap_max_pool_percent / 100 <
 368                 zswap_pool_pages);
 369 }
 370
 371 /*
 372  * Carries out the common pattern of freeing and entry's zsmalloc allocation,
 373  * freeing the entry itself, and decrementing the number of stored pages.
 374  */
 375 static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry)
 376 {
 377         zbud_free(tree->pool, entry->handle);
 378         zswap_entry_cache_free(entry);
 379         atomic_dec(&zswap_stored_pages);
 380         zswap_pool_pages = zbud_get_pool_size(tree->pool);
 381 }
 382
 383 /*********************************
 384 * writeback code
 385 **********************************/
 386 /* return enum for zswap_get_swap_cache_page */
 387 enum zswap_get_swap_ret {
 388         ZSWAP_SWAPCACHE_NEW,
 389         ZSWAP_SWAPCACHE_EXIST,
 390         ZSWAP_SWAPCACHE_NOMEM
 391 };
 392
 393 /*
 394  * zswap_get_swap_cache_page
 395  *
 396  * This is an adaption of read_swap_cache_async()
 397  *
 398  * This function tries to find a page with the given swap entry
 399  * in the swapper_space address space (the swap cache).  If the page
 400  * is found, it is returned in retpage.  Otherwise, a page is allocated,
 401  * added to the swap cache, and returned in retpage.
 402  *
 403  * If success, the swap cache page is returned in retpage
 404  * Returns 0 if page was already in the swap cache, page is not locked
 405  * Returns 1 if the new page needs to be populated, page is locked
 406  * Returns <0 on error
 407  */
 408 static int zswap_get_swap_cache_page(swp_entry_t entry,
 409                                 struct page **retpage)
 410 {
 411         struct page *found_page, *new_page = NULL;
 412         struct address_space *swapper_space = &swapper_spaces[swp_type(entry)];
 413         int err;
 414
 415         *retpage = NULL;
 416         do {
 417                 /*
 418                  * First check the swap cache.  Since this is normally
 419                  * called after lookup_swap_cache() failed, re-calling
 420                  * that would confuse statistics.
 421                  */
 422                 found_page = find_get_page(swapper_space, entry.val);
 423                 if (found_page)
 424                         break;
 425
 426                 /*
 427                  * Get a new page to read into from swap.
 428                  */
 429                 if (!new_page) {
 430                         new_page = alloc_page(GFP_KERNEL);
 431                         if (!new_page)
 432                                 break; /* Out of memory */
 433                 }
 434
 435                 /*
 436                  * call radix_tree_preload() while we can wait.
 437                  */
 438                 err = radix_tree_preload(GFP_KERNEL);
 439                 if (err)
 440                         break;
 441
 442                 /*
 443                  * Swap entry may have been freed since our caller observed it.
 444                  */
 445                 err = swapcache_prepare(entry);
 446                 if (err == -EEXIST) { /* seems racy */
 447                         radix_tree_preload_end();
 448                         continue;
 449                 }
 450                 if (err) { /* swp entry is obsolete ? */
 451                         radix_tree_preload_end();
 452                         break;
 453                 }
 454
 455                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
 456                 __set_page_locked(new_page);
 457                 SetPageSwapBacked(new_page);
 458                 err = __add_to_swap_cache(new_page, entry);
 459                 if (likely(!err)) {
 460                         radix_tree_preload_end();
 461                         lru_cache_add_anon(new_page);
 462                         *retpage = new_page;
 463                         return ZSWAP_SWAPCACHE_NEW;
 464                 }
 465                 radix_tree_preload_end();
 466                 ClearPageSwapBacked(new_page);
 467                 __clear_page_locked(new_page);
 468                 /*
 469                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
 470                  * clear SWAP_HAS_CACHE flag.
 471                  */
 472                 swapcache_free(entry, NULL);
 473         } while (err != -ENOMEM);
 474
 475         if (new_page)
 476                 page_cache_release(new_page);
 477         if (!found_page)
 478                 return ZSWAP_SWAPCACHE_NOMEM;
 479         *retpage = found_page;
 480         return ZSWAP_SWAPCACHE_EXIST;
 481 }
 482
 483 /*
 484  * Attempts to free an entry by adding a page to the swap cache,
 485  * decompressing the entry data into the page, and issuing a
 486  * bio write to write the page back to the swap device.
 487  *
 488  * This can be thought of as a "resumed writeback" of the page
 489  * to the swap device.  We are basically resuming the same swap
 490  * writeback path that was intercepted with the frontswap_store()
 491  * in the first place.  After the page has been decompressed into
 492  * the swap cache, the compressed version stored by zswap can be
 493  * freed.
 494  */
 495 static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle)
 496 {
 497         struct zswap_header *zhdr;
 498         swp_entry_t swpentry;
 499         struct zswap_tree *tree;
 500         pgoff_t offset;
 501         struct zswap_entry *entry;
 502         struct page *page;
 503         u8 *src, *dst;
 504         unsigned int dlen;
 505         int ret, refcount;
 506         struct writeback_control wbc = {
 507                 .sync_mode = WB_SYNC_NONE,
 508         };
 509
 510         /* extract swpentry from data */
 511         zhdr = zbud_map(pool, handle);
 512         swpentry = zhdr->swpentry; /* here */
 513         zbud_unmap(pool, handle);
 514         tree = zswap_trees[swp_type(swpentry)];
 515         offset = swp_offset(swpentry);
 516         BUG_ON(pool != tree->pool);
 517
 518         /* find and ref zswap entry */
 519         spin_lock(&tree->lock);
 520         entry = zswap_rb_search(&tree->rbroot, offset);
 521         if (!entry) {
 522                 /* entry was invalidated */
 523                 spin_unlock(&tree->lock);
 524                 return 0;
 525         }
 526         zswap_entry_get(entry);
 527         spin_unlock(&tree->lock);
 528         BUG_ON(offset != entry->offset);
 529
 530         /* try to allocate swap cache page */
 531         switch (zswap_get_swap_cache_page(swpentry, &page)) {
 532         case ZSWAP_SWAPCACHE_NOMEM: /* no memory */
 533                 ret = -ENOMEM;
 534                 goto fail;
 535
 536         case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */
 537                 /* page is already in the swap cache, ignore for now */
 538                 page_cache_release(page);
 539                 ret = -EEXIST;
 540                 goto fail;
 541
 542         case ZSWAP_SWAPCACHE_NEW: /* page is locked */
 543                 /* decompress */
 544                 dlen = PAGE_SIZE;
 545                 src = (u8 *)zbud_map(tree->pool, entry->handle) +
 546                         sizeof(struct zswap_header);
 547                 dst = kmap_atomic(page);
 548                 ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
 549                                 entry->length, dst, &dlen);
 550                 kunmap_atomic(dst);
 551                 zbud_unmap(tree->pool, entry->handle);
 552                 BUG_ON(ret);
 553                 BUG_ON(dlen != PAGE_SIZE);
 554
 555                 /* page is up to date */
 556                 SetPageUptodate(page);
 557         }
 558
 559         /* start writeback */
 560         __swap_writepage(page, &wbc, end_swap_bio_write);
 561         page_cache_release(page);
 562         zswap_written_back_pages++;
 563
 564         spin_lock(&tree->lock);
 565
 566         /* drop local reference */
 567         zswap_entry_put(entry);
 568         /* drop the initial reference from entry creation */
 569         refcount = zswap_entry_put(entry);
 570
 571         /*
 572          * There are three possible values for refcount here:
 573          * (1) refcount is 1, load is in progress, unlink from rbtree,
 574          *     load will free
 575          * (2) refcount is 0, (normal case) entry is valid,
 576          *     remove from rbtree and free entry
 577          * (3) refcount is -1, invalidate happened during writeback,
 578          *     free entry
 579          */
 580         if (refcount >= 0) {
 581                 /* no invalidate yet, remove from rbtree */
 582                 rb_erase(&entry->rbnode, &tree->rbroot);
 583         }
 584         spin_unlock(&tree->lock);
 585         if (refcount <= 0) {
 586                 /* free the entry */
 587                 zswap_free_entry(tree, entry);
 588                 return 0;
 589         }
 590         return -EAGAIN;
 591
 592 fail:
 593         spin_lock(&tree->lock);
 594         zswap_entry_put(entry);
 595         spin_unlock(&tree->lock);
 596         return ret;
 597 }
 598
 599 /*********************************
 600 * frontswap hooks
 601 **********************************/
 602 /* attempts to compress and store an single page */
 603 static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 604                                 struct page *page)
 605 {
 606         struct zswap_tree *tree = zswap_trees[type];
 607         struct zswap_entry *entry, *dupentry;
 608         int ret;
 609         unsigned int dlen = PAGE_SIZE, len;
 610         unsigned long handle;
 611         char *buf;
 612         u8 *src, *dst;
 613         struct zswap_header *zhdr;
 614
 615         if (!tree) {
 616                 ret = -ENODEV;
 617                 goto reject;
 618         }
 619
 620         /* reclaim space if needed */
 621         if (zswap_is_full()) {
 622                 zswap_pool_limit_hit++;
 623                 if (zbud_reclaim_page(tree->pool, 8)) {
 624                         zswap_reject_reclaim_fail++;
 625                         ret = -ENOMEM;
 626                         goto reject;
 627                 }
 628         }
 629
 630         /* allocate entry */
 631         entry = zswap_entry_cache_alloc(GFP_KERNEL);
 632         if (!entry) {
 633                 zswap_reject_kmemcache_fail++;
 634                 ret = -ENOMEM;
 635                 goto reject;
 636         }
 637
 638         /* compress */
 639         dst = get_cpu_var(zswap_dstmem);
 640         src = kmap_atomic(page);
 641         ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
 642         kunmap_atomic(src);
 643         if (ret) {
 644                 ret = -EINVAL;
 645                 goto freepage;
 646         }
 647
 648         /* store */
 649         len = dlen + sizeof(struct zswap_header);
 650         ret = zbud_alloc(tree->pool, len, __GFP_NORETRY | __GFP_NOWARN,
 651                 &handle);
 652         if (ret == -ENOSPC) {
 653                 zswap_reject_compress_poor++;
 654                 goto freepage;
 655         }
 656         if (ret) {
 657                 zswap_reject_alloc_fail++;
 658                 goto freepage;
 659         }
 660         zhdr = zbud_map(tree->pool, handle);
 661         zhdr->swpentry = swp_entry(type, offset);
 662         buf = (u8 *)(zhdr + 1);
 663         memcpy(buf, dst, dlen);
 664         zbud_unmap(tree->pool, handle);
 665         put_cpu_var(zswap_dstmem);
 666
 667         /* populate entry */
 668         entry->offset = offset;
 669         entry->handle = handle;
 670         entry->length = dlen;
 671
 672         /* map */
 673         spin_lock(&tree->lock);
 674         do {
 675                 ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
 676                 if (ret == -EEXIST) {
 677                         zswap_duplicate_entry++;
 678                         /* remove from rbtree */
 679                         rb_erase(&dupentry->rbnode, &tree->rbroot);
 680                         if (!zswap_entry_put(dupentry)) {
 681                                 /* free */
 682                                 zswap_free_entry(tree, dupentry);
 683                         }
 684                 }
 685         } while (ret == -EEXIST);
 686         spin_unlock(&tree->lock);
 687
 688         /* update stats */
 689         atomic_inc(&zswap_stored_pages);
 690         zswap_pool_pages = zbud_get_pool_size(tree->pool);
 691
 692         return 0;
 693
 694 freepage:
 695         put_cpu_var(zswap_dstmem);
 696         zswap_entry_cache_free(entry);
 697 reject:
 698         return ret;
 699 }
 700
 701 /*
 702  * returns 0 if the page was successfully decompressed
 703  * return -1 on entry not found or error
 704 */
 705 static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 706                                 struct page *page)
 707 {
 708         struct zswap_tree *tree = zswap_trees[type];
 709         struct zswap_entry *entry;
 710         u8 *src, *dst;
 711         unsigned int dlen;
 712         int refcount, ret;
 713
 714         /* find */
 715         spin_lock(&tree->lock);
 716         entry = zswap_rb_search(&tree->rbroot, offset);
 717         if (!entry) {
 718                 /* entry was written back */
 719                 spin_unlock(&tree->lock);
 720                 return -1;
 721         }
 722         zswap_entry_get(entry);
 723         spin_unlock(&tree->lock);
 724
 725         /* decompress */
 726         dlen = PAGE_SIZE;
 727         src = (u8 *)zbud_map(tree->pool, entry->handle) +
 728                         sizeof(struct zswap_header);
 729         dst = kmap_atomic(page);
 730         ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
 731                 dst, &dlen);
 732         kunmap_atomic(dst);
 733         zbud_unmap(tree->pool, entry->handle);
 734         BUG_ON(ret);
 735
 736         spin_lock(&tree->lock);
 737         refcount = zswap_entry_put(entry);
 738         if (likely(refcount)) {
 739                 spin_unlock(&tree->lock);
 740                 return 0;
 741         }
 742         spin_unlock(&tree->lock);
 743
 744         /*
 745          * We don't have to unlink from the rbtree because
 746          * zswap_writeback_entry() or zswap_frontswap_invalidate page()
 747          * has already done this for us if we are the last reference.
 748          */
 749         /* free */
 750
 751         zswap_free_entry(tree, entry);
 752
 753         return 0;
 754 }
 755
 756 /* frees an entry in zswap */
 757 static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
 758 {
 759         struct zswap_tree *tree = zswap_trees[type];
 760         struct zswap_entry *entry;
 761         int refcount;
 762
 763         /* find */
 764         spin_lock(&tree->lock);
 765         entry = zswap_rb_search(&tree->rbroot, offset);
 766         if (!entry) {
 767                 /* entry was written back */
 768                 spin_unlock(&tree->lock);
 769                 return;
 770         }
 771
 772         /* remove from rbtree */
 773         rb_erase(&entry->rbnode, &tree->rbroot);
 774
 775         /* drop the initial reference from entry creation */
 776         refcount = zswap_entry_put(entry);
 777
 778         spin_unlock(&tree->lock);
 779
 780         if (refcount) {
 781                 /* writeback in progress, writeback will free */
 782                 return;
 783         }
 784
 785         /* free */
 786         zswap_free_entry(tree, entry);
 787 }
 788
 789 /* frees all zswap entries for the given swap type */
 790 static void zswap_frontswap_invalidate_area(unsigned type)
 791 {
 792         struct zswap_tree *tree = zswap_trees[type];
 793         struct rb_node *node;
 794         struct zswap_entry *entry;
 795
 796         if (!tree)
 797                 return;
 798
 799         /* walk the tree and free everything */
 800         spin_lock(&tree->lock);
 801         /*
 802          * TODO: Even though this code should not be executed because
 803          * the try_to_unuse() in swapoff should have emptied the tree,
 804          * it is very wasteful to rebalance the tree after every
 805          * removal when we are freeing the whole tree.
 806          *
 807          * If post-order traversal code is ever added to the rbtree
 808          * implementation, it should be used here.
 809          */
 810         while ((node = rb_first(&tree->rbroot))) {
 811                 entry = rb_entry(node, struct zswap_entry, rbnode);
 812                 rb_erase(&entry->rbnode, &tree->rbroot);
 813                 zbud_free(tree->pool, entry->handle);
 814                 zswap_entry_cache_free(entry);
 815                 atomic_dec(&zswap_stored_pages);
 816         }
 817         tree->rbroot = RB_ROOT;
 818         spin_unlock(&tree->lock);
 819 }
 820
 821 static struct zbud_ops zswap_zbud_ops = {
 822         .evict = zswap_writeback_entry
 823 };
 824
 825 static void zswap_frontswap_init(unsigned type)
 826 {
 827         struct zswap_tree *tree;
 828
 829         tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL);
 830         if (!tree)
 831                 goto err;
 832         tree->pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_ops);
 833         if (!tree->pool)
 834                 goto freetree;
 835         tree->rbroot = RB_ROOT;
 836         spin_lock_init(&tree->lock);
 837         zswap_trees[type] = tree;
 838         return;
 839
 840 freetree:
 841         kfree(tree);
 842 err:
 843         pr_err("alloc failed, zswap disabled for swap type %d\n", type);
 844 }
 845
 846 static struct frontswap_ops zswap_frontswap_ops = {
 847         .store = zswap_frontswap_store,
 848         .load = zswap_frontswap_load,
 849         .invalidate_page = zswap_frontswap_invalidate_page,
 850         .invalidate_area = zswap_frontswap_invalidate_area,
 851         .init = zswap_frontswap_init
 852 };
 853
 854 /*********************************
 855 * debugfs functions
 856 **********************************/
 857 #ifdef CONFIG_DEBUG_FS
 858 #include <linux/debugfs.h>
 859
 860 static struct dentry *zswap_debugfs_root;
 861
 862 static int __init zswap_debugfs_init(void)
 863 {
 864         if (!debugfs_initialized())
 865                 return -ENODEV;
 866
 867         zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
 868         if (!zswap_debugfs_root)
 869                 return -ENOMEM;
 870
 871         debugfs_create_u64("pool_limit_hit", S_IRUGO,
 872                         zswap_debugfs_root, &zswap_pool_limit_hit);
 873         debugfs_create_u64("reject_reclaim_fail", S_IRUGO,
 874                         zswap_debugfs_root, &zswap_reject_reclaim_fail);
 875         debugfs_create_u64("reject_alloc_fail", S_IRUGO,
 876                         zswap_debugfs_root, &zswap_reject_alloc_fail);
 877         debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
 878                         zswap_debugfs_root, &zswap_reject_kmemcache_fail);
 879         debugfs_create_u64("reject_compress_poor", S_IRUGO,
 880                         zswap_debugfs_root, &zswap_reject_compress_poor);
 881         debugfs_create_u64("written_back_pages", S_IRUGO,
 882                         zswap_debugfs_root, &zswap_written_back_pages);
 883         debugfs_create_u64("duplicate_entry", S_IRUGO,
 884                         zswap_debugfs_root, &zswap_duplicate_entry);
 885         debugfs_create_u64("pool_pages", S_IRUGO,
 886                         zswap_debugfs_root, &zswap_pool_pages);
 887         debugfs_create_atomic_t("stored_pages", S_IRUGO,
 888                         zswap_debugfs_root, &zswap_stored_pages);
 889
 890         return 0;
 891 }
 892
 893 static void __exit zswap_debugfs_exit(void)
 894 {
 895         debugfs_remove_recursive(zswap_debugfs_root);
 896 }
 897 #else
 898 static int __init zswap_debugfs_init(void)
 899 {
 900         return 0;
 901 }
 902
 903 static void __exit zswap_debugfs_exit(void) { }
 904 #endif
 905
 906 /*********************************
 907 * module init and exit
 908 **********************************/
 909 static int __init init_zswap(void)
 910 {
 911         if (!zswap_enabled)
 912                 return 0;
 913
 914         pr_info("loading zswap\n");
 915         if (zswap_entry_cache_create()) {
 916                 pr_err("entry cache creation failed\n");
 917                 goto error;
 918         }
 919         if (zswap_comp_init()) {
 920                 pr_err("compressor initialization failed\n");
 921                 goto compfail;
 922         }
 923         if (zswap_cpu_init()) {
 924                 pr_err("per-cpu initialization failed\n");
 925                 goto pcpufail;
 926         }
 927         frontswap_register_ops(&zswap_frontswap_ops);
 928         if (zswap_debugfs_init())
 929                 pr_warn("debugfs initialization failed\n");
 930         return 0;
 931 pcpufail:
 932         zswap_comp_exit();
 933 compfail:
 934         zswap_entry_cache_destory();
 935 error:
 936         return -ENOMEM;
 937 }
 938 /* must be late so crypto has time to come up */
 939 late_initcall(init_zswap);
 940
 941 MODULE_LICENSE("GPL");
 942 MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
 943 MODULE_DESCRIPTION("Compressed cache for swap pages");