mm/z3fold.c

   1 /*
   2  * z3fold.c
   3  *
   4  * Author: Vitaly Wool <vitaly.wool@konsulko.com>
   5  * Copyright (C) 2016, Sony Mobile Communications Inc.
   6  *
   7  * This implementation is based on zbud written by Seth Jennings.
   8  *
   9  * z3fold is an special purpose allocator for storing compressed pages. It
  10  * can store up to three compressed pages per page which improves the
  11  * compression ratio of zbud while retaining its main concepts (e. g. always
  12  * storing an integral number of objects per page) and simplicity.
  13  * It still has simple and deterministic reclaim properties that make it
  14  * preferable to a higher density approach (with no requirement on integral
  15  * number of object per page) when reclaim is used.
  16  *
  17  * As in zbud, pages are divided into "chunks".  The size of the chunks is
  18  * fixed at compile time and is determined by NCHUNKS_ORDER below.
  19  *
  20  * z3fold doesn't export any API and is meant to be used via zpool API.
  21  */
  22
  23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  24
  25 #include <linux/atomic.h>
  26 #include <linux/sched.h>
  27 #include <linux/list.h>
  28 #include <linux/mm.h>
  29 #include <linux/module.h>
  30 #include <linux/percpu.h>
  31 #include <linux/preempt.h>
  32 #include <linux/workqueue.h>
  33 #include <linux/slab.h>
  34 #include <linux/spinlock.h>
  35 #include <linux/zpool.h>
  36
  37 /*****************
  38  * Structures
  39 *****************/
  40 struct z3fold_pool;
  41 struct z3fold_ops {
  42         int (*evict)(struct z3fold_pool *pool, unsigned long handle);
  43 };
  44
  45 enum buddy {
  46         HEADLESS = 0,
  47         FIRST,
  48         MIDDLE,
  49         LAST,
  50         BUDDIES_MAX
  51 };
  52
  53 /*
  54  * struct z3fold_header - z3fold page metadata occupying first chunks of each
  55  *                      z3fold page, except for HEADLESS pages
  56  * @buddy:              links the z3fold page into the relevant list in the
  57  *                      pool
  58  * @page_lock:          per-page lock
  59  * @refcount:           reference count for the z3fold page
  60  * @work:               work_struct for page layout optimization
  61  * @pool:               pointer to the pool which this page belongs to
  62  * @cpu:                CPU which this page "belongs" to
  63  * @first_chunks:       the size of the first buddy in chunks, 0 if free
  64  * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
  65  * @last_chunks:        the size of the last buddy in chunks, 0 if free
  66  * @first_num:          the starting number (for the first handle)
  67  */
  68 struct z3fold_header {
  69         struct list_head buddy;
  70         spinlock_t page_lock;
  71         struct kref refcount;
  72         struct work_struct work;
  73         struct z3fold_pool *pool;
  74         short cpu;
  75         unsigned short first_chunks;
  76         unsigned short middle_chunks;
  77         unsigned short last_chunks;
  78         unsigned short start_middle;
  79         unsigned short first_num:2;
  80 };
  81
  82 /*
  83  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
  84  * adjusting internal fragmentation.  It also determines the number of
  85  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
  86  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
  87  * in the beginning of an allocated page are occupied by z3fold header, so
  88  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
  89  * which shows the max number of free chunks in z3fold page, also there will
  90  * be 63, or 62, respectively, freelists per pool.
  91  */
  92 #define NCHUNKS_ORDER   6
  93
  94 #define CHUNK_SHIFT     (PAGE_SHIFT - NCHUNKS_ORDER)
  95 #define CHUNK_SIZE      (1 << CHUNK_SHIFT)
  96 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
  97 #define ZHDR_CHUNKS     (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
  98 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
  99 #define NCHUNKS         ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
 100
 101 #define BUDDY_MASK      (0x3)
 102
 103 /**
 104  * struct z3fold_pool - stores metadata for each z3fold pool
 105  * @name:       pool name
 106  * @lock:       protects pool unbuddied/lru lists
 107  * @stale_lock: protects pool stale page list
 108  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
 109  *              buddies; the list each z3fold page is added to depends on
 110  *              the size of its free region.
 111  * @lru:        list tracking the z3fold pages in LRU order by most recently
 112  *              added buddy.
 113  * @stale:      list of pages marked for freeing
 114  * @pages_nr:   number of z3fold pages in the pool.
 115  * @ops:        pointer to a structure of user defined operations specified at
 116  *              pool creation time.
 117  * @compact_wq: workqueue for page layout background optimization
 118  * @release_wq: workqueue for safe page release
 119  * @work:       work_struct for safe page release
 120  *
 121  * This structure is allocated at pool creation time and maintains metadata
 122  * pertaining to a particular z3fold pool.
 123  */
 124 struct z3fold_pool {
 125         const char *name;
 126         spinlock_t lock;
 127         spinlock_t stale_lock;
 128         struct list_head *unbuddied;
 129         struct list_head lru;
 130         struct list_head stale;
 131         atomic64_t pages_nr;
 132         const struct z3fold_ops *ops;
 133         struct zpool *zpool;
 134         const struct zpool_ops *zpool_ops;
 135         struct workqueue_struct *compact_wq;
 136         struct workqueue_struct *release_wq;
 137         struct work_struct work;
 138 };
 139
 140 /*
 141  * Internal z3fold page flags
 142  */
 143 enum z3fold_page_flags {
 144         PAGE_HEADLESS = 0,
 145         MIDDLE_CHUNK_MAPPED,
 146         NEEDS_COMPACTING,
 147         PAGE_STALE
 148 };
 149
 150 /*****************
 151  * Helpers
 152 *****************/
 153
 154 /* Converts an allocation size in bytes to size in z3fold chunks */
 155 static int size_to_chunks(size_t size)
 156 {
 157         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 158 }
 159
 160 #define for_each_unbuddied_list(_iter, _begin) \
 161         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 162
 163 static void compact_page_work(struct work_struct *w);
 164
 165 /* Initializes the z3fold header of a newly allocated z3fold page */
 166 static struct z3fold_header *init_z3fold_page(struct page *page,
 167                                         struct z3fold_pool *pool)
 168 {
 169         struct z3fold_header *zhdr = page_address(page);
 170
 171         INIT_LIST_HEAD(&page->lru);
 172         clear_bit(PAGE_HEADLESS, &page->private);
 173         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 174         clear_bit(NEEDS_COMPACTING, &page->private);
 175         clear_bit(PAGE_STALE, &page->private);
 176
 177         spin_lock_init(&zhdr->page_lock);
 178         kref_init(&zhdr->refcount);
 179         zhdr->first_chunks = 0;
 180         zhdr->middle_chunks = 0;
 181         zhdr->last_chunks = 0;
 182         zhdr->first_num = 0;
 183         zhdr->start_middle = 0;
 184         zhdr->cpu = -1;
 185         zhdr->pool = pool;
 186         INIT_LIST_HEAD(&zhdr->buddy);
 187         INIT_WORK(&zhdr->work, compact_page_work);
 188         return zhdr;
 189 }
 190
 191 /* Resets the struct page fields and frees the page */
 192 static void free_z3fold_page(struct page *page)
 193 {
 194         __free_page(page);
 195 }
 196
 197 /* Lock a z3fold page */
 198 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 199 {
 200         spin_lock(&zhdr->page_lock);
 201 }
 202
 203 /* Try to lock a z3fold page */
 204 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 205 {
 206         return spin_trylock(&zhdr->page_lock);
 207 }
 208
 209 /* Unlock a z3fold page */
 210 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 211 {
 212         spin_unlock(&zhdr->page_lock);
 213 }
 214
 215 /*
 216  * Encodes the handle of a particular buddy within a z3fold page
 217  * Pool lock should be held as this function accesses first_num
 218  */
 219 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 220 {
 221         unsigned long handle;
 222
 223         handle = (unsigned long)zhdr;
 224         if (bud != HEADLESS)
 225                 handle += (bud + zhdr->first_num) & BUDDY_MASK;
 226         return handle;
 227 }
 228
 229 /* Returns the z3fold page where a given handle is stored */
 230 static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
 231 {
 232         return (struct z3fold_header *)(handle & PAGE_MASK);
 233 }
 234
 235 /*
 236  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
 237  *  but that doesn't matter. because the masking will result in the
 238  *  correct buddy number.
 239  */
 240 static enum buddy handle_to_buddy(unsigned long handle)
 241 {
 242         struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
 243         return (handle - zhdr->first_num) & BUDDY_MASK;
 244 }
 245
 246 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 247 {
 248         struct page *page = virt_to_page(zhdr);
 249         struct z3fold_pool *pool = zhdr->pool;
 250
 251         WARN_ON(!list_empty(&zhdr->buddy));
 252         set_bit(PAGE_STALE, &page->private);
 253         clear_bit(NEEDS_COMPACTING, &page->private);
 254         spin_lock(&pool->lock);
 255         if (!list_empty(&page->lru))
 256                 list_del(&page->lru);
 257         spin_unlock(&pool->lock);
 258         if (locked)
 259                 z3fold_page_unlock(zhdr);
 260         spin_lock(&pool->stale_lock);
 261         list_add(&zhdr->buddy, &pool->stale);
 262         queue_work(pool->release_wq, &pool->work);
 263         spin_unlock(&pool->stale_lock);
 264 }
 265
 266 static void __attribute__((__unused__))
 267                         release_z3fold_page(struct kref *ref)
 268 {
 269         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 270                                                 refcount);
 271         __release_z3fold_page(zhdr, false);
 272 }
 273
 274 static void release_z3fold_page_locked(struct kref *ref)
 275 {
 276         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 277                                                 refcount);
 278         WARN_ON(z3fold_page_trylock(zhdr));
 279         __release_z3fold_page(zhdr, true);
 280 }
 281
 282 static void release_z3fold_page_locked_list(struct kref *ref)
 283 {
 284         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 285                                                refcount);
 286         spin_lock(&zhdr->pool->lock);
 287         list_del_init(&zhdr->buddy);
 288         spin_unlock(&zhdr->pool->lock);
 289
 290         WARN_ON(z3fold_page_trylock(zhdr));
 291         __release_z3fold_page(zhdr, true);
 292 }
 293
 294 static void free_pages_work(struct work_struct *w)
 295 {
 296         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 297
 298         spin_lock(&pool->stale_lock);
 299         while (!list_empty(&pool->stale)) {
 300                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
 301                                                 struct z3fold_header, buddy);
 302                 struct page *page = virt_to_page(zhdr);
 303
 304                 list_del(&zhdr->buddy);
 305                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
 306                         continue;
 307                 spin_unlock(&pool->stale_lock);
 308                 cancel_work_sync(&zhdr->work);
 309                 free_z3fold_page(page);
 310                 cond_resched();
 311                 spin_lock(&pool->stale_lock);
 312         }
 313         spin_unlock(&pool->stale_lock);
 314 }
 315
 316 /*
 317  * Returns the number of free chunks in a z3fold page.
 318  * NB: can't be used with HEADLESS pages.
 319  */
 320 static int num_free_chunks(struct z3fold_header *zhdr)
 321 {
 322         int nfree;
 323         /*
 324          * If there is a middle object, pick up the bigger free space
 325          * either before or after it. Otherwise just subtract the number
 326          * of chunks occupied by the first and the last objects.
 327          */
 328         if (zhdr->middle_chunks != 0) {
 329                 int nfree_before = zhdr->first_chunks ?
 330                         0 : zhdr->start_middle - ZHDR_CHUNKS;
 331                 int nfree_after = zhdr->last_chunks ?
 332                         0 : TOTAL_CHUNKS -
 333                                 (zhdr->start_middle + zhdr->middle_chunks);
 334                 nfree = max(nfree_before, nfree_after);
 335         } else
 336                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
 337         return nfree;
 338 }
 339
 340 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 341                                 unsigned short dst_chunk)
 342 {
 343         void *beg = zhdr;
 344         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
 345                        beg + (zhdr->start_middle << CHUNK_SHIFT),
 346                        zhdr->middle_chunks << CHUNK_SHIFT);
 347 }
 348
 349 #define BIG_CHUNK_GAP   3
 350 /* Has to be called with lock held */
 351 static int z3fold_compact_page(struct z3fold_header *zhdr)
 352 {
 353         struct page *page = virt_to_page(zhdr);
 354
 355         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 356                 return 0; /* can't move middle chunk, it's used */
 357
 358         if (zhdr->middle_chunks == 0)
 359                 return 0; /* nothing to compact */
 360
 361         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
 362                 /* move to the beginning */
 363                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
 364                 zhdr->first_chunks = zhdr->middle_chunks;
 365                 zhdr->middle_chunks = 0;
 366                 zhdr->start_middle = 0;
 367                 zhdr->first_num++;
 368                 return 1;
 369         }
 370
 371         /*
 372          * moving data is expensive, so let's only do that if
 373          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
 374          */
 375         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
 376             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
 377                         BIG_CHUNK_GAP) {
 378                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
 379                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 380                 return 1;
 381         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
 382                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
 383                                         + zhdr->middle_chunks) >=
 384                         BIG_CHUNK_GAP) {
 385                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
 386                         zhdr->middle_chunks;
 387                 mchunk_memmove(zhdr, new_start);
 388                 zhdr->start_middle = new_start;
 389                 return 1;
 390         }
 391
 392         return 0;
 393 }
 394
 395 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 396 {
 397         struct z3fold_pool *pool = zhdr->pool;
 398         struct page *page;
 399         struct list_head *unbuddied;
 400         int fchunks;
 401
 402         page = virt_to_page(zhdr);
 403         if (locked)
 404                 WARN_ON(z3fold_page_trylock(zhdr));
 405         else
 406                 z3fold_page_lock(zhdr);
 407         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
 408                 z3fold_page_unlock(zhdr);
 409                 return;
 410         }
 411         spin_lock(&pool->lock);
 412         list_del_init(&zhdr->buddy);
 413         spin_unlock(&pool->lock);
 414
 415         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
 416                 atomic64_dec(&pool->pages_nr);
 417                 return;
 418         }
 419
 420         z3fold_compact_page(zhdr);
 421         unbuddied = get_cpu_ptr(pool->unbuddied);
 422         fchunks = num_free_chunks(zhdr);
 423         if (fchunks < NCHUNKS &&
 424             (!zhdr->first_chunks || !zhdr->middle_chunks ||
 425                         !zhdr->last_chunks)) {
 426                 /* the page's not completely free and it's unbuddied */
 427                 spin_lock(&pool->lock);
 428                 list_add(&zhdr->buddy, &unbuddied[fchunks]);
 429                 spin_unlock(&pool->lock);
 430                 zhdr->cpu = smp_processor_id();
 431         }
 432         put_cpu_ptr(pool->unbuddied);
 433         z3fold_page_unlock(zhdr);
 434 }
 435
 436 static void compact_page_work(struct work_struct *w)
 437 {
 438         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
 439                                                 work);
 440
 441         do_compact_page(zhdr, false);
 442 }
 443
 444
 445 /*
 446  * API Functions
 447  */
 448
 449 /**
 450  * z3fold_create_pool() - create a new z3fold pool
 451  * @name:       pool name
 452  * @gfp:        gfp flags when allocating the z3fold pool structure
 453  * @ops:        user-defined operations for the z3fold pool
 454  *
 455  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
 456  * failed.
 457  */
 458 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
 459                 const struct z3fold_ops *ops)
 460 {
 461         struct z3fold_pool *pool = NULL;
 462         int i, cpu;
 463
 464         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
 465         if (!pool)
 466                 goto out;
 467         spin_lock_init(&pool->lock);
 468         spin_lock_init(&pool->stale_lock);
 469         pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
 470         for_each_possible_cpu(cpu) {
 471                 struct list_head *unbuddied =
 472                                 per_cpu_ptr(pool->unbuddied, cpu);
 473                 for_each_unbuddied_list(i, 0)
 474                         INIT_LIST_HEAD(&unbuddied[i]);
 475         }
 476         INIT_LIST_HEAD(&pool->lru);
 477         INIT_LIST_HEAD(&pool->stale);
 478         atomic64_set(&pool->pages_nr, 0);
 479         pool->name = name;
 480         pool->compact_wq = create_singlethread_workqueue(pool->name);
 481         if (!pool->compact_wq)
 482                 goto out;
 483         pool->release_wq = create_singlethread_workqueue(pool->name);
 484         if (!pool->release_wq)
 485                 goto out_wq;
 486         INIT_WORK(&pool->work, free_pages_work);
 487         pool->ops = ops;
 488         return pool;
 489
 490 out_wq:
 491         destroy_workqueue(pool->compact_wq);
 492 out:
 493         kfree(pool);
 494         return NULL;
 495 }
 496
 497 /**
 498  * z3fold_destroy_pool() - destroys an existing z3fold pool
 499  * @pool:       the z3fold pool to be destroyed
 500  *
 501  * The pool should be emptied before this function is called.
 502  */
 503 static void z3fold_destroy_pool(struct z3fold_pool *pool)
 504 {
 505         destroy_workqueue(pool->release_wq);
 506         destroy_workqueue(pool->compact_wq);
 507         kfree(pool);
 508 }
 509
 510 /**
 511  * z3fold_alloc() - allocates a region of a given size
 512  * @pool:       z3fold pool from which to allocate
 513  * @size:       size in bytes of the desired allocation
 514  * @gfp:        gfp flags used if the pool needs to grow
 515  * @handle:     handle of the new allocation
 516  *
 517  * This function will attempt to find a free region in the pool large enough to
 518  * satisfy the allocation request.  A search of the unbuddied lists is
 519  * performed first. If no suitable free region is found, then a new page is
 520  * allocated and added to the pool to satisfy the request.
 521  *
 522  * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
 523  * as z3fold pool pages.
 524  *
 525  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
 526  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
 527  * a new page.
 528  */
 529 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 530                         unsigned long *handle)
 531 {
 532         int chunks = 0, i, freechunks;
 533         struct z3fold_header *zhdr = NULL;
 534         struct page *page = NULL;
 535         enum buddy bud;
 536         bool can_sleep = (gfp & __GFP_RECLAIM) == __GFP_RECLAIM;
 537
 538         if (!size || (gfp & __GFP_HIGHMEM))
 539                 return -EINVAL;
 540
 541         if (size > PAGE_SIZE)
 542                 return -ENOSPC;
 543
 544         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
 545                 bud = HEADLESS;
 546         else {
 547                 struct list_head *unbuddied;
 548                 chunks = size_to_chunks(size);
 549
 550 lookup:
 551                 /* First, try to find an unbuddied z3fold page. */
 552                 unbuddied = get_cpu_ptr(pool->unbuddied);
 553                 for_each_unbuddied_list(i, chunks) {
 554                         struct list_head *l = &unbuddied[i];
 555
 556                         zhdr = list_first_entry_or_null(READ_ONCE(l),
 557                                                 struct z3fold_header, buddy);
 558
 559                         if (!zhdr)
 560                                 continue;
 561
 562                         /* Re-check under lock. */
 563                         spin_lock(&pool->lock);
 564                         l = &unbuddied[i];
 565                         if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
 566                                         struct z3fold_header, buddy)) ||
 567                             !z3fold_page_trylock(zhdr)) {
 568                                 spin_unlock(&pool->lock);
 569                                 put_cpu_ptr(pool->unbuddied);
 570                                 goto lookup;
 571                         }
 572                         list_del_init(&zhdr->buddy);
 573                         zhdr->cpu = -1;
 574                         spin_unlock(&pool->lock);
 575
 576                         page = virt_to_page(zhdr);
 577                         if (test_bit(NEEDS_COMPACTING, &page->private)) {
 578                                 z3fold_page_unlock(zhdr);
 579                                 zhdr = NULL;
 580                                 put_cpu_ptr(pool->unbuddied);
 581                                 if (can_sleep)
 582                                         cond_resched();
 583                                 goto lookup;
 584                         }
 585
 586                         /*
 587                          * this page could not be removed from its unbuddied
 588                          * list while pool lock was held, and then we've taken
 589                          * page lock so kref_put could not be called before
 590                          * we got here, so it's safe to just call kref_get()
 591                          */
 592                         kref_get(&zhdr->refcount);
 593                         break;
 594                 }
 595                 put_cpu_ptr(pool->unbuddied);
 596
 597                 if (zhdr) {
 598                         if (zhdr->first_chunks == 0) {
 599                                 if (zhdr->middle_chunks != 0 &&
 600                                     chunks >= zhdr->start_middle)
 601                                         bud = LAST;
 602                                 else
 603                                         bud = FIRST;
 604                         } else if (zhdr->last_chunks == 0)
 605                                 bud = LAST;
 606                         else if (zhdr->middle_chunks == 0)
 607                                 bud = MIDDLE;
 608                         else {
 609                                 if (kref_put(&zhdr->refcount,
 610                                              release_z3fold_page_locked))
 611                                         atomic64_dec(&pool->pages_nr);
 612                                 else
 613                                         z3fold_page_unlock(zhdr);
 614                                 pr_err("No free chunks in unbuddied\n");
 615                                 WARN_ON(1);
 616                                 goto lookup;
 617                         }
 618                         goto found;
 619                 }
 620                 bud = FIRST;
 621         }
 622
 623         spin_lock(&pool->stale_lock);
 624         zhdr = list_first_entry_or_null(&pool->stale,
 625                                         struct z3fold_header, buddy);
 626         /*
 627          * Before allocating a page, let's see if we can take one from the
 628          * stale pages list. cancel_work_sync() can sleep so we must make
 629          * sure it won't be called in case we're in atomic context.
 630          */
 631         if (zhdr && (can_sleep || !work_pending(&zhdr->work))) {
 632                 list_del(&zhdr->buddy);
 633                 spin_unlock(&pool->stale_lock);
 634                 if (can_sleep)
 635                         cancel_work_sync(&zhdr->work);
 636                 page = virt_to_page(zhdr);
 637         } else {
 638                 spin_unlock(&pool->stale_lock);
 639                 page = alloc_page(gfp);
 640         }
 641
 642         if (!page)
 643                 return -ENOMEM;
 644
 645         atomic64_inc(&pool->pages_nr);
 646         zhdr = init_z3fold_page(page, pool);
 647
 648         if (bud == HEADLESS) {
 649                 set_bit(PAGE_HEADLESS, &page->private);
 650                 goto headless;
 651         }
 652         z3fold_page_lock(zhdr);
 653
 654 found:
 655         if (bud == FIRST)
 656                 zhdr->first_chunks = chunks;
 657         else if (bud == LAST)
 658                 zhdr->last_chunks = chunks;
 659         else {
 660                 zhdr->middle_chunks = chunks;
 661                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 662         }
 663
 664         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 665                         zhdr->middle_chunks == 0) {
 666                 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
 667
 668                 /* Add to unbuddied list */
 669                 freechunks = num_free_chunks(zhdr);
 670                 spin_lock(&pool->lock);
 671                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
 672                 spin_unlock(&pool->lock);
 673                 zhdr->cpu = smp_processor_id();
 674                 put_cpu_ptr(pool->unbuddied);
 675         }
 676
 677 headless:
 678         spin_lock(&pool->lock);
 679         /* Add/move z3fold page to beginning of LRU */
 680         if (!list_empty(&page->lru))
 681                 list_del(&page->lru);
 682
 683         list_add(&page->lru, &pool->lru);
 684
 685         *handle = encode_handle(zhdr, bud);
 686         spin_unlock(&pool->lock);
 687         if (bud != HEADLESS)
 688                 z3fold_page_unlock(zhdr);
 689
 690         return 0;
 691 }
 692
 693 /**
 694  * z3fold_free() - frees the allocation associated with the given handle
 695  * @pool:       pool in which the allocation resided
 696  * @handle:     handle associated with the allocation returned by z3fold_alloc()
 697  *
 698  * In the case that the z3fold page in which the allocation resides is under
 699  * reclaim, as indicated by the PG_reclaim flag being set, this function
 700  * only sets the first|last_chunks to 0.  The page is actually freed
 701  * once both buddies are evicted (see z3fold_reclaim_page() below).
 702  */
 703 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 704 {
 705         struct z3fold_header *zhdr;
 706         struct page *page;
 707         enum buddy bud;
 708
 709         zhdr = handle_to_z3fold_header(handle);
 710         page = virt_to_page(zhdr);
 711
 712         if (test_bit(PAGE_HEADLESS, &page->private)) {
 713                 /* HEADLESS page stored */
 714                 bud = HEADLESS;
 715         } else {
 716                 z3fold_page_lock(zhdr);
 717                 bud = handle_to_buddy(handle);
 718
 719                 switch (bud) {
 720                 case FIRST:
 721                         zhdr->first_chunks = 0;
 722                         break;
 723                 case MIDDLE:
 724                         zhdr->middle_chunks = 0;
 725                         zhdr->start_middle = 0;
 726                         break;
 727                 case LAST:
 728                         zhdr->last_chunks = 0;
 729                         break;
 730                 default:
 731                         pr_err("%s: unknown bud %d\n", __func__, bud);
 732                         WARN_ON(1);
 733                         z3fold_page_unlock(zhdr);
 734                         return;
 735                 }
 736         }
 737
 738         if (bud == HEADLESS) {
 739                 spin_lock(&pool->lock);
 740                 list_del(&page->lru);
 741                 spin_unlock(&pool->lock);
 742                 free_z3fold_page(page);
 743                 atomic64_dec(&pool->pages_nr);
 744                 return;
 745         }
 746
 747         if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 748                 atomic64_dec(&pool->pages_nr);
 749                 return;
 750         }
 751         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
 752                 z3fold_page_unlock(zhdr);
 753                 return;
 754         }
 755         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
 756                 spin_lock(&pool->lock);
 757                 list_del_init(&zhdr->buddy);
 758                 spin_unlock(&pool->lock);
 759                 zhdr->cpu = -1;
 760                 kref_get(&zhdr->refcount);
 761                 do_compact_page(zhdr, true);
 762                 return;
 763         }
 764         kref_get(&zhdr->refcount);
 765         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
 766         z3fold_page_unlock(zhdr);
 767 }
 768
 769 /**
 770  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
 771  * @pool:       pool from which a page will attempt to be evicted
 772  * @retires:    number of pages on the LRU list for which eviction will
 773  *              be attempted before failing
 774  *
 775  * z3fold reclaim is different from normal system reclaim in that it is done
 776  * from the bottom, up. This is because only the bottom layer, z3fold, has
 777  * information on how the allocations are organized within each z3fold page.
 778  * This has the potential to create interesting locking situations between
 779  * z3fold and the user, however.
 780  *
 781  * To avoid these, this is how z3fold_reclaim_page() should be called:
 782
 783  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
 784  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
 785  * call the user-defined eviction handler with the pool and handle as
 786  * arguments.
 787  *
 788  * If the handle can not be evicted, the eviction handler should return
 789  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
 790  * appropriate list and try the next z3fold page on the LRU up to
 791  * a user defined number of retries.
 792  *
 793  * If the handle is successfully evicted, the eviction handler should
 794  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
 795  * contains logic to delay freeing the page if the page is under reclaim,
 796  * as indicated by the setting of the PG_reclaim flag on the underlying page.
 797  *
 798  * If all buddies in the z3fold page are successfully evicted, then the
 799  * z3fold page can be freed.
 800  *
 801  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
 802  * no pages to evict or an eviction handler is not registered, -EAGAIN if
 803  * the retry limit was hit.
 804  */
 805 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 806 {
 807         int i, ret = 0;
 808         struct z3fold_header *zhdr = NULL;
 809         struct page *page = NULL;
 810         struct list_head *pos;
 811         unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
 812
 813         spin_lock(&pool->lock);
 814         if (!pool->ops || !pool->ops->evict || retries == 0) {
 815                 spin_unlock(&pool->lock);
 816                 return -EINVAL;
 817         }
 818         for (i = 0; i < retries; i++) {
 819                 if (list_empty(&pool->lru)) {
 820                         spin_unlock(&pool->lock);
 821                         return -EINVAL;
 822                 }
 823                 list_for_each_prev(pos, &pool->lru) {
 824                         page = list_entry(pos, struct page, lru);
 825                         if (test_bit(PAGE_HEADLESS, &page->private))
 826                                 /* candidate found */
 827                                 break;
 828
 829                         zhdr = page_address(page);
 830                         if (!z3fold_page_trylock(zhdr))
 831                                 continue; /* can't evict at this point */
 832                         kref_get(&zhdr->refcount);
 833                         list_del_init(&zhdr->buddy);
 834                         zhdr->cpu = -1;
 835                 }
 836
 837                 list_del_init(&page->lru);
 838                 spin_unlock(&pool->lock);
 839
 840                 if (!test_bit(PAGE_HEADLESS, &page->private)) {
 841                         /*
 842                          * We need encode the handles before unlocking, since
 843                          * we can race with free that will set
 844                          * (first|last)_chunks to 0
 845                          */
 846                         first_handle = 0;
 847                         last_handle = 0;
 848                         middle_handle = 0;
 849                         if (zhdr->first_chunks)
 850                                 first_handle = encode_handle(zhdr, FIRST);
 851                         if (zhdr->middle_chunks)
 852                                 middle_handle = encode_handle(zhdr, MIDDLE);
 853                         if (zhdr->last_chunks)
 854                                 last_handle = encode_handle(zhdr, LAST);
 855                         /*
 856                          * it's safe to unlock here because we hold a
 857                          * reference to this page
 858                          */
 859                         z3fold_page_unlock(zhdr);
 860                 } else {
 861                         first_handle = encode_handle(zhdr, HEADLESS);
 862                         last_handle = middle_handle = 0;
 863                 }
 864
 865                 /* Issue the eviction callback(s) */
 866                 if (middle_handle) {
 867                         ret = pool->ops->evict(pool, middle_handle);
 868                         if (ret)
 869                                 goto next;
 870                 }
 871                 if (first_handle) {
 872                         ret = pool->ops->evict(pool, first_handle);
 873                         if (ret)
 874                                 goto next;
 875                 }
 876                 if (last_handle) {
 877                         ret = pool->ops->evict(pool, last_handle);
 878                         if (ret)
 879                                 goto next;
 880                 }
 881 next:
 882                 spin_lock(&pool->lock);
 883                 if (test_bit(PAGE_HEADLESS, &page->private)) {
 884                         if (ret == 0) {
 885                                 spin_unlock(&pool->lock);
 886                                 free_z3fold_page(page);
 887                                 return 0;
 888                         }
 889                 } else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
 890                         atomic64_dec(&pool->pages_nr);
 891                         spin_unlock(&pool->lock);
 892                         return 0;
 893                 }
 894
 895                 /*
 896                  * Add to the beginning of LRU.
 897                  * Pool lock has to be kept here to ensure the page has
 898                  * not already been released
 899                  */
 900                 list_add(&page->lru, &pool->lru);
 901         }
 902         spin_unlock(&pool->lock);
 903         return -EAGAIN;
 904 }
 905
 906 /**
 907  * z3fold_map() - maps the allocation associated with the given handle
 908  * @pool:       pool in which the allocation resides
 909  * @handle:     handle associated with the allocation to be mapped
 910  *
 911  * Extracts the buddy number from handle and constructs the pointer to the
 912  * correct starting chunk within the page.
 913  *
 914  * Returns: a pointer to the mapped allocation
 915  */
 916 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
 917 {
 918         struct z3fold_header *zhdr;
 919         struct page *page;
 920         void *addr;
 921         enum buddy buddy;
 922
 923         zhdr = handle_to_z3fold_header(handle);
 924         addr = zhdr;
 925         page = virt_to_page(zhdr);
 926
 927         if (test_bit(PAGE_HEADLESS, &page->private))
 928                 goto out;
 929
 930         z3fold_page_lock(zhdr);
 931         buddy = handle_to_buddy(handle);
 932         switch (buddy) {
 933         case FIRST:
 934                 addr += ZHDR_SIZE_ALIGNED;
 935                 break;
 936         case MIDDLE:
 937                 addr += zhdr->start_middle << CHUNK_SHIFT;
 938                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 939                 break;
 940         case LAST:
 941                 addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
 942                 break;
 943         default:
 944                 pr_err("unknown buddy id %d\n", buddy);
 945                 WARN_ON(1);
 946                 addr = NULL;
 947                 break;
 948         }
 949
 950         z3fold_page_unlock(zhdr);
 951 out:
 952         return addr;
 953 }
 954
 955 /**
 956  * z3fold_unmap() - unmaps the allocation associated with the given handle
 957  * @pool:       pool in which the allocation resides
 958  * @handle:     handle associated with the allocation to be unmapped
 959  */
 960 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
 961 {
 962         struct z3fold_header *zhdr;
 963         struct page *page;
 964         enum buddy buddy;
 965
 966         zhdr = handle_to_z3fold_header(handle);
 967         page = virt_to_page(zhdr);
 968
 969         if (test_bit(PAGE_HEADLESS, &page->private))
 970                 return;
 971
 972         z3fold_page_lock(zhdr);
 973         buddy = handle_to_buddy(handle);
 974         if (buddy == MIDDLE)
 975                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 976         z3fold_page_unlock(zhdr);
 977 }
 978
 979 /**
 980  * z3fold_get_pool_size() - gets the z3fold pool size in pages
 981  * @pool:       pool whose size is being queried
 982  *
 983  * Returns: size in pages of the given pool.
 984  */
 985 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
 986 {
 987         return atomic64_read(&pool->pages_nr);
 988 }
 989
 990 /*****************
 991  * zpool
 992  ****************/
 993
 994 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
 995 {
 996         if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
 997                 return pool->zpool_ops->evict(pool->zpool, handle);
 998         else
 999                 return -ENOENT;
1000 }
1001
1002 static const struct z3fold_ops z3fold_zpool_ops = {
1003         .evict =        z3fold_zpool_evict
1004 };
1005
1006 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
1007                                const struct zpool_ops *zpool_ops,
1008                                struct zpool *zpool)
1009 {
1010         struct z3fold_pool *pool;
1011
1012         pool = z3fold_create_pool(name, gfp,
1013                                 zpool_ops ? &z3fold_zpool_ops : NULL);
1014         if (pool) {
1015                 pool->zpool = zpool;
1016                 pool->zpool_ops = zpool_ops;
1017         }
1018         return pool;
1019 }
1020
1021 static void z3fold_zpool_destroy(void *pool)
1022 {
1023         z3fold_destroy_pool(pool);
1024 }
1025
1026 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1027                         unsigned long *handle)
1028 {
1029         return z3fold_alloc(pool, size, gfp, handle);
1030 }
1031 static void z3fold_zpool_free(void *pool, unsigned long handle)
1032 {
1033         z3fold_free(pool, handle);
1034 }
1035
1036 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
1037                         unsigned int *reclaimed)
1038 {
1039         unsigned int total = 0;
1040         int ret = -EINVAL;
1041
1042         while (total < pages) {
1043                 ret = z3fold_reclaim_page(pool, 8);
1044                 if (ret < 0)
1045                         break;
1046                 total++;
1047         }
1048
1049         if (reclaimed)
1050                 *reclaimed = total;
1051
1052         return ret;
1053 }
1054
1055 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1056                         enum zpool_mapmode mm)
1057 {
1058         return z3fold_map(pool, handle);
1059 }
1060 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1061 {
1062         z3fold_unmap(pool, handle);
1063 }
1064
1065 static u64 z3fold_zpool_total_size(void *pool)
1066 {
1067         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1068 }
1069
1070 static struct zpool_driver z3fold_zpool_driver = {
1071         .type =         "z3fold",
1072         .owner =        THIS_MODULE,
1073         .create =       z3fold_zpool_create,
1074         .destroy =      z3fold_zpool_destroy,
1075         .malloc =       z3fold_zpool_malloc,
1076         .free =         z3fold_zpool_free,
1077         .shrink =       z3fold_zpool_shrink,
1078         .map =          z3fold_zpool_map,
1079         .unmap =        z3fold_zpool_unmap,
1080         .total_size =   z3fold_zpool_total_size,
1081 };
1082
1083 MODULE_ALIAS("zpool-z3fold");
1084
1085 static int __init init_z3fold(void)
1086 {
1087         /* Make sure the z3fold header is not larger than the page size */
1088         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
1089         zpool_register_driver(&z3fold_zpool_driver);
1090
1091         return 0;
1092 }
1093
1094 static void __exit exit_z3fold(void)
1095 {
1096         zpool_unregister_driver(&z3fold_zpool_driver);
1097 }
1098
1099 module_init(init_z3fold);
1100 module_exit(exit_z3fold);
1101
1102 MODULE_LICENSE("GPL");
1103 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1104 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");