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         UNDER_RECLAIM
 149 };
 150
 151 /*****************
 152  * Helpers
 153 *****************/
 154
 155 /* Converts an allocation size in bytes to size in z3fold chunks */
 156 static int size_to_chunks(size_t size)
 157 {
 158         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 159 }
 160
 161 #define for_each_unbuddied_list(_iter, _begin) \
 162         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 163
 164 static void compact_page_work(struct work_struct *w);
 165
 166 /* Initializes the z3fold header of a newly allocated z3fold page */
 167 static struct z3fold_header *init_z3fold_page(struct page *page,
 168                                         struct z3fold_pool *pool)
 169 {
 170         struct z3fold_header *zhdr = page_address(page);
 171
 172         INIT_LIST_HEAD(&page->lru);
 173         clear_bit(PAGE_HEADLESS, &page->private);
 174         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 175         clear_bit(NEEDS_COMPACTING, &page->private);
 176         clear_bit(PAGE_STALE, &page->private);
 177         clear_bit(UNDER_RECLAIM, &page->private);
 178
 179         spin_lock_init(&zhdr->page_lock);
 180         kref_init(&zhdr->refcount);
 181         zhdr->first_chunks = 0;
 182         zhdr->middle_chunks = 0;
 183         zhdr->last_chunks = 0;
 184         zhdr->first_num = 0;
 185         zhdr->start_middle = 0;
 186         zhdr->cpu = -1;
 187         zhdr->pool = pool;
 188         INIT_LIST_HEAD(&zhdr->buddy);
 189         INIT_WORK(&zhdr->work, compact_page_work);
 190         return zhdr;
 191 }
 192
 193 /* Resets the struct page fields and frees the page */
 194 static void free_z3fold_page(struct page *page)
 195 {
 196         __free_page(page);
 197 }
 198
 199 /* Lock a z3fold page */
 200 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 201 {
 202         spin_lock(&zhdr->page_lock);
 203 }
 204
 205 /* Try to lock a z3fold page */
 206 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 207 {
 208         return spin_trylock(&zhdr->page_lock);
 209 }
 210
 211 /* Unlock a z3fold page */
 212 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 213 {
 214         spin_unlock(&zhdr->page_lock);
 215 }
 216
 217 /*
 218  * Encodes the handle of a particular buddy within a z3fold page
 219  * Pool lock should be held as this function accesses first_num
 220  */
 221 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 222 {
 223         unsigned long handle;
 224
 225         handle = (unsigned long)zhdr;
 226         if (bud != HEADLESS)
 227                 handle += (bud + zhdr->first_num) & BUDDY_MASK;
 228         return handle;
 229 }
 230
 231 /* Returns the z3fold page where a given handle is stored */
 232 static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
 233 {
 234         return (struct z3fold_header *)(handle & PAGE_MASK);
 235 }
 236
 237 /*
 238  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
 239  *  but that doesn't matter. because the masking will result in the
 240  *  correct buddy number.
 241  */
 242 static enum buddy handle_to_buddy(unsigned long handle)
 243 {
 244         struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
 245         return (handle - zhdr->first_num) & BUDDY_MASK;
 246 }
 247
 248 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 249 {
 250         struct page *page = virt_to_page(zhdr);
 251         struct z3fold_pool *pool = zhdr->pool;
 252
 253         WARN_ON(!list_empty(&zhdr->buddy));
 254         set_bit(PAGE_STALE, &page->private);
 255         clear_bit(NEEDS_COMPACTING, &page->private);
 256         spin_lock(&pool->lock);
 257         if (!list_empty(&page->lru))
 258                 list_del(&page->lru);
 259         spin_unlock(&pool->lock);
 260         if (locked)
 261                 z3fold_page_unlock(zhdr);
 262         spin_lock(&pool->stale_lock);
 263         list_add(&zhdr->buddy, &pool->stale);
 264         queue_work(pool->release_wq, &pool->work);
 265         spin_unlock(&pool->stale_lock);
 266 }
 267
 268 static void __attribute__((__unused__))
 269                         release_z3fold_page(struct kref *ref)
 270 {
 271         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 272                                                 refcount);
 273         __release_z3fold_page(zhdr, false);
 274 }
 275
 276 static void release_z3fold_page_locked(struct kref *ref)
 277 {
 278         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 279                                                 refcount);
 280         WARN_ON(z3fold_page_trylock(zhdr));
 281         __release_z3fold_page(zhdr, true);
 282 }
 283
 284 static void release_z3fold_page_locked_list(struct kref *ref)
 285 {
 286         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 287                                                refcount);
 288         spin_lock(&zhdr->pool->lock);
 289         list_del_init(&zhdr->buddy);
 290         spin_unlock(&zhdr->pool->lock);
 291
 292         WARN_ON(z3fold_page_trylock(zhdr));
 293         __release_z3fold_page(zhdr, true);
 294 }
 295
 296 static void free_pages_work(struct work_struct *w)
 297 {
 298         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 299
 300         spin_lock(&pool->stale_lock);
 301         while (!list_empty(&pool->stale)) {
 302                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
 303                                                 struct z3fold_header, buddy);
 304                 struct page *page = virt_to_page(zhdr);
 305
 306                 list_del(&zhdr->buddy);
 307                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
 308                         continue;
 309                 spin_unlock(&pool->stale_lock);
 310                 cancel_work_sync(&zhdr->work);
 311                 free_z3fold_page(page);
 312                 cond_resched();
 313                 spin_lock(&pool->stale_lock);
 314         }
 315         spin_unlock(&pool->stale_lock);
 316 }
 317
 318 /*
 319  * Returns the number of free chunks in a z3fold page.
 320  * NB: can't be used with HEADLESS pages.
 321  */
 322 static int num_free_chunks(struct z3fold_header *zhdr)
 323 {
 324         int nfree;
 325         /*
 326          * If there is a middle object, pick up the bigger free space
 327          * either before or after it. Otherwise just subtract the number
 328          * of chunks occupied by the first and the last objects.
 329          */
 330         if (zhdr->middle_chunks != 0) {
 331                 int nfree_before = zhdr->first_chunks ?
 332                         0 : zhdr->start_middle - ZHDR_CHUNKS;
 333                 int nfree_after = zhdr->last_chunks ?
 334                         0 : TOTAL_CHUNKS -
 335                                 (zhdr->start_middle + zhdr->middle_chunks);
 336                 nfree = max(nfree_before, nfree_after);
 337         } else
 338                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
 339         return nfree;
 340 }
 341
 342 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 343                                 unsigned short dst_chunk)
 344 {
 345         void *beg = zhdr;
 346         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
 347                        beg + (zhdr->start_middle << CHUNK_SHIFT),
 348                        zhdr->middle_chunks << CHUNK_SHIFT);
 349 }
 350
 351 #define BIG_CHUNK_GAP   3
 352 /* Has to be called with lock held */
 353 static int z3fold_compact_page(struct z3fold_header *zhdr)
 354 {
 355         struct page *page = virt_to_page(zhdr);
 356
 357         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 358                 return 0; /* can't move middle chunk, it's used */
 359
 360         if (zhdr->middle_chunks == 0)
 361                 return 0; /* nothing to compact */
 362
 363         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
 364                 /* move to the beginning */
 365                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
 366                 zhdr->first_chunks = zhdr->middle_chunks;
 367                 zhdr->middle_chunks = 0;
 368                 zhdr->start_middle = 0;
 369                 zhdr->first_num++;
 370                 return 1;
 371         }
 372
 373         /*
 374          * moving data is expensive, so let's only do that if
 375          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
 376          */
 377         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
 378             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
 379                         BIG_CHUNK_GAP) {
 380                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
 381                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 382                 return 1;
 383         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
 384                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
 385                                         + zhdr->middle_chunks) >=
 386                         BIG_CHUNK_GAP) {
 387                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
 388                         zhdr->middle_chunks;
 389                 mchunk_memmove(zhdr, new_start);
 390                 zhdr->start_middle = new_start;
 391                 return 1;
 392         }
 393
 394         return 0;
 395 }
 396
 397 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 398 {
 399         struct z3fold_pool *pool = zhdr->pool;
 400         struct page *page;
 401         struct list_head *unbuddied;
 402         int fchunks;
 403
 404         page = virt_to_page(zhdr);
 405         if (locked)
 406                 WARN_ON(z3fold_page_trylock(zhdr));
 407         else
 408                 z3fold_page_lock(zhdr);
 409         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
 410                 z3fold_page_unlock(zhdr);
 411                 return;
 412         }
 413         spin_lock(&pool->lock);
 414         list_del_init(&zhdr->buddy);
 415         spin_unlock(&pool->lock);
 416
 417         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
 418                 atomic64_dec(&pool->pages_nr);
 419                 return;
 420         }
 421
 422         z3fold_compact_page(zhdr);
 423         unbuddied = get_cpu_ptr(pool->unbuddied);
 424         fchunks = num_free_chunks(zhdr);
 425         if (fchunks < NCHUNKS &&
 426             (!zhdr->first_chunks || !zhdr->middle_chunks ||
 427                         !zhdr->last_chunks)) {
 428                 /* the page's not completely free and it's unbuddied */
 429                 spin_lock(&pool->lock);
 430                 list_add(&zhdr->buddy, &unbuddied[fchunks]);
 431                 spin_unlock(&pool->lock);
 432                 zhdr->cpu = smp_processor_id();
 433         }
 434         put_cpu_ptr(pool->unbuddied);
 435         z3fold_page_unlock(zhdr);
 436 }
 437
 438 static void compact_page_work(struct work_struct *w)
 439 {
 440         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
 441                                                 work);
 442
 443         do_compact_page(zhdr, false);
 444 }
 445
 446
 447 /*
 448  * API Functions
 449  */
 450
 451 /**
 452  * z3fold_create_pool() - create a new z3fold pool
 453  * @name:       pool name
 454  * @gfp:        gfp flags when allocating the z3fold pool structure
 455  * @ops:        user-defined operations for the z3fold pool
 456  *
 457  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
 458  * failed.
 459  */
 460 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
 461                 const struct z3fold_ops *ops)
 462 {
 463         struct z3fold_pool *pool = NULL;
 464         int i, cpu;
 465
 466         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
 467         if (!pool)
 468                 goto out;
 469         spin_lock_init(&pool->lock);
 470         spin_lock_init(&pool->stale_lock);
 471         pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
 472         if (!pool->unbuddied)
 473                 goto out_pool;
 474         for_each_possible_cpu(cpu) {
 475                 struct list_head *unbuddied =
 476                                 per_cpu_ptr(pool->unbuddied, cpu);
 477                 for_each_unbuddied_list(i, 0)
 478                         INIT_LIST_HEAD(&unbuddied[i]);
 479         }
 480         INIT_LIST_HEAD(&pool->lru);
 481         INIT_LIST_HEAD(&pool->stale);
 482         atomic64_set(&pool->pages_nr, 0);
 483         pool->name = name;
 484         pool->compact_wq = create_singlethread_workqueue(pool->name);
 485         if (!pool->compact_wq)
 486                 goto out_unbuddied;
 487         pool->release_wq = create_singlethread_workqueue(pool->name);
 488         if (!pool->release_wq)
 489                 goto out_wq;
 490         INIT_WORK(&pool->work, free_pages_work);
 491         pool->ops = ops;
 492         return pool;
 493
 494 out_wq:
 495         destroy_workqueue(pool->compact_wq);
 496 out_unbuddied:
 497         free_percpu(pool->unbuddied);
 498 out_pool:
 499         kfree(pool);
 500 out:
 501         return NULL;
 502 }
 503
 504 /**
 505  * z3fold_destroy_pool() - destroys an existing z3fold pool
 506  * @pool:       the z3fold pool to be destroyed
 507  *
 508  * The pool should be emptied before this function is called.
 509  */
 510 static void z3fold_destroy_pool(struct z3fold_pool *pool)
 511 {
 512         destroy_workqueue(pool->release_wq);
 513         destroy_workqueue(pool->compact_wq);
 514         kfree(pool);
 515 }
 516
 517 /**
 518  * z3fold_alloc() - allocates a region of a given size
 519  * @pool:       z3fold pool from which to allocate
 520  * @size:       size in bytes of the desired allocation
 521  * @gfp:        gfp flags used if the pool needs to grow
 522  * @handle:     handle of the new allocation
 523  *
 524  * This function will attempt to find a free region in the pool large enough to
 525  * satisfy the allocation request.  A search of the unbuddied lists is
 526  * performed first. If no suitable free region is found, then a new page is
 527  * allocated and added to the pool to satisfy the request.
 528  *
 529  * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
 530  * as z3fold pool pages.
 531  *
 532  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
 533  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
 534  * a new page.
 535  */
 536 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 537                         unsigned long *handle)
 538 {
 539         int chunks = 0, i, freechunks;
 540         struct z3fold_header *zhdr = NULL;
 541         struct page *page = NULL;
 542         enum buddy bud;
 543         bool can_sleep = gfpflags_allow_blocking(gfp);
 544
 545         if (!size || (gfp & __GFP_HIGHMEM))
 546                 return -EINVAL;
 547
 548         if (size > PAGE_SIZE)
 549                 return -ENOSPC;
 550
 551         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
 552                 bud = HEADLESS;
 553         else {
 554                 struct list_head *unbuddied;
 555                 chunks = size_to_chunks(size);
 556
 557 lookup:
 558                 /* First, try to find an unbuddied z3fold page. */
 559                 unbuddied = get_cpu_ptr(pool->unbuddied);
 560                 for_each_unbuddied_list(i, chunks) {
 561                         struct list_head *l = &unbuddied[i];
 562
 563                         zhdr = list_first_entry_or_null(READ_ONCE(l),
 564                                                 struct z3fold_header, buddy);
 565
 566                         if (!zhdr)
 567                                 continue;
 568
 569                         /* Re-check under lock. */
 570                         spin_lock(&pool->lock);
 571                         l = &unbuddied[i];
 572                         if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
 573                                         struct z3fold_header, buddy)) ||
 574                             !z3fold_page_trylock(zhdr)) {
 575                                 spin_unlock(&pool->lock);
 576                                 put_cpu_ptr(pool->unbuddied);
 577                                 goto lookup;
 578                         }
 579                         list_del_init(&zhdr->buddy);
 580                         zhdr->cpu = -1;
 581                         spin_unlock(&pool->lock);
 582
 583                         page = virt_to_page(zhdr);
 584                         if (test_bit(NEEDS_COMPACTING, &page->private)) {
 585                                 z3fold_page_unlock(zhdr);
 586                                 zhdr = NULL;
 587                                 put_cpu_ptr(pool->unbuddied);
 588                                 if (can_sleep)
 589                                         cond_resched();
 590                                 goto lookup;
 591                         }
 592
 593                         /*
 594                          * this page could not be removed from its unbuddied
 595                          * list while pool lock was held, and then we've taken
 596                          * page lock so kref_put could not be called before
 597                          * we got here, so it's safe to just call kref_get()
 598                          */
 599                         kref_get(&zhdr->refcount);
 600                         break;
 601                 }
 602                 put_cpu_ptr(pool->unbuddied);
 603
 604                 if (zhdr) {
 605                         if (zhdr->first_chunks == 0) {
 606                                 if (zhdr->middle_chunks != 0 &&
 607                                     chunks >= zhdr->start_middle)
 608                                         bud = LAST;
 609                                 else
 610                                         bud = FIRST;
 611                         } else if (zhdr->last_chunks == 0)
 612                                 bud = LAST;
 613                         else if (zhdr->middle_chunks == 0)
 614                                 bud = MIDDLE;
 615                         else {
 616                                 if (kref_put(&zhdr->refcount,
 617                                              release_z3fold_page_locked))
 618                                         atomic64_dec(&pool->pages_nr);
 619                                 else
 620                                         z3fold_page_unlock(zhdr);
 621                                 pr_err("No free chunks in unbuddied\n");
 622                                 WARN_ON(1);
 623                                 goto lookup;
 624                         }
 625                         goto found;
 626                 }
 627                 bud = FIRST;
 628         }
 629
 630         page = NULL;
 631         if (can_sleep) {
 632                 spin_lock(&pool->stale_lock);
 633                 zhdr = list_first_entry_or_null(&pool->stale,
 634                                                 struct z3fold_header, buddy);
 635                 /*
 636                  * Before allocating a page, let's see if we can take one from
 637                  * the stale pages list. cancel_work_sync() can sleep so we
 638                  * limit this case to the contexts where we can sleep
 639                  */
 640                 if (zhdr) {
 641                         list_del(&zhdr->buddy);
 642                         spin_unlock(&pool->stale_lock);
 643                         cancel_work_sync(&zhdr->work);
 644                         page = virt_to_page(zhdr);
 645                 } else {
 646                         spin_unlock(&pool->stale_lock);
 647                 }
 648         }
 649         if (!page)
 650                 page = alloc_page(gfp);
 651
 652         if (!page)
 653                 return -ENOMEM;
 654
 655         atomic64_inc(&pool->pages_nr);
 656         zhdr = init_z3fold_page(page, pool);
 657
 658         if (bud == HEADLESS) {
 659                 set_bit(PAGE_HEADLESS, &page->private);
 660                 goto headless;
 661         }
 662         z3fold_page_lock(zhdr);
 663
 664 found:
 665         if (bud == FIRST)
 666                 zhdr->first_chunks = chunks;
 667         else if (bud == LAST)
 668                 zhdr->last_chunks = chunks;
 669         else {
 670                 zhdr->middle_chunks = chunks;
 671                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 672         }
 673
 674         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 675                         zhdr->middle_chunks == 0) {
 676                 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
 677
 678                 /* Add to unbuddied list */
 679                 freechunks = num_free_chunks(zhdr);
 680                 spin_lock(&pool->lock);
 681                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
 682                 spin_unlock(&pool->lock);
 683                 zhdr->cpu = smp_processor_id();
 684                 put_cpu_ptr(pool->unbuddied);
 685         }
 686
 687 headless:
 688         spin_lock(&pool->lock);
 689         /* Add/move z3fold page to beginning of LRU */
 690         if (!list_empty(&page->lru))
 691                 list_del(&page->lru);
 692
 693         list_add(&page->lru, &pool->lru);
 694
 695         *handle = encode_handle(zhdr, bud);
 696         spin_unlock(&pool->lock);
 697         if (bud != HEADLESS)
 698                 z3fold_page_unlock(zhdr);
 699
 700         return 0;
 701 }
 702
 703 /**
 704  * z3fold_free() - frees the allocation associated with the given handle
 705  * @pool:       pool in which the allocation resided
 706  * @handle:     handle associated with the allocation returned by z3fold_alloc()
 707  *
 708  * In the case that the z3fold page in which the allocation resides is under
 709  * reclaim, as indicated by the PG_reclaim flag being set, this function
 710  * only sets the first|last_chunks to 0.  The page is actually freed
 711  * once both buddies are evicted (see z3fold_reclaim_page() below).
 712  */
 713 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 714 {
 715         struct z3fold_header *zhdr;
 716         struct page *page;
 717         enum buddy bud;
 718
 719         zhdr = handle_to_z3fold_header(handle);
 720         page = virt_to_page(zhdr);
 721
 722         if (test_bit(PAGE_HEADLESS, &page->private)) {
 723                 /* HEADLESS page stored */
 724                 bud = HEADLESS;
 725         } else {
 726                 z3fold_page_lock(zhdr);
 727                 bud = handle_to_buddy(handle);
 728
 729                 switch (bud) {
 730                 case FIRST:
 731                         zhdr->first_chunks = 0;
 732                         break;
 733                 case MIDDLE:
 734                         zhdr->middle_chunks = 0;
 735                         zhdr->start_middle = 0;
 736                         break;
 737                 case LAST:
 738                         zhdr->last_chunks = 0;
 739                         break;
 740                 default:
 741                         pr_err("%s: unknown bud %d\n", __func__, bud);
 742                         WARN_ON(1);
 743                         z3fold_page_unlock(zhdr);
 744                         return;
 745                 }
 746         }
 747
 748         if (bud == HEADLESS) {
 749                 spin_lock(&pool->lock);
 750                 list_del(&page->lru);
 751                 spin_unlock(&pool->lock);
 752                 free_z3fold_page(page);
 753                 atomic64_dec(&pool->pages_nr);
 754                 return;
 755         }
 756
 757         if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 758                 atomic64_dec(&pool->pages_nr);
 759                 return;
 760         }
 761         if (test_bit(UNDER_RECLAIM, &page->private)) {
 762                 z3fold_page_unlock(zhdr);
 763                 return;
 764         }
 765         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
 766                 z3fold_page_unlock(zhdr);
 767                 return;
 768         }
 769         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
 770                 spin_lock(&pool->lock);
 771                 list_del_init(&zhdr->buddy);
 772                 spin_unlock(&pool->lock);
 773                 zhdr->cpu = -1;
 774                 kref_get(&zhdr->refcount);
 775                 do_compact_page(zhdr, true);
 776                 return;
 777         }
 778         kref_get(&zhdr->refcount);
 779         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
 780         z3fold_page_unlock(zhdr);
 781 }
 782
 783 /**
 784  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
 785  * @pool:       pool from which a page will attempt to be evicted
 786  * @retries:    number of pages on the LRU list for which eviction will
 787  *              be attempted before failing
 788  *
 789  * z3fold reclaim is different from normal system reclaim in that it is done
 790  * from the bottom, up. This is because only the bottom layer, z3fold, has
 791  * information on how the allocations are organized within each z3fold page.
 792  * This has the potential to create interesting locking situations between
 793  * z3fold and the user, however.
 794  *
 795  * To avoid these, this is how z3fold_reclaim_page() should be called:
 796  *
 797  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
 798  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
 799  * call the user-defined eviction handler with the pool and handle as
 800  * arguments.
 801  *
 802  * If the handle can not be evicted, the eviction handler should return
 803  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
 804  * appropriate list and try the next z3fold page on the LRU up to
 805  * a user defined number of retries.
 806  *
 807  * If the handle is successfully evicted, the eviction handler should
 808  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
 809  * contains logic to delay freeing the page if the page is under reclaim,
 810  * as indicated by the setting of the PG_reclaim flag on the underlying page.
 811  *
 812  * If all buddies in the z3fold page are successfully evicted, then the
 813  * z3fold page can be freed.
 814  *
 815  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
 816  * no pages to evict or an eviction handler is not registered, -EAGAIN if
 817  * the retry limit was hit.
 818  */
 819 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 820 {
 821         int i, ret = 0;
 822         struct z3fold_header *zhdr = NULL;
 823         struct page *page = NULL;
 824         struct list_head *pos;
 825         unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
 826
 827         spin_lock(&pool->lock);
 828         if (!pool->ops || !pool->ops->evict || retries == 0) {
 829                 spin_unlock(&pool->lock);
 830                 return -EINVAL;
 831         }
 832         for (i = 0; i < retries; i++) {
 833                 if (list_empty(&pool->lru)) {
 834                         spin_unlock(&pool->lock);
 835                         return -EINVAL;
 836                 }
 837                 list_for_each_prev(pos, &pool->lru) {
 838                         page = list_entry(pos, struct page, lru);
 839                         if (test_bit(PAGE_HEADLESS, &page->private))
 840                                 /* candidate found */
 841                                 break;
 842
 843                         zhdr = page_address(page);
 844                         if (!z3fold_page_trylock(zhdr))
 845                                 continue; /* can't evict at this point */
 846                         kref_get(&zhdr->refcount);
 847                         list_del_init(&zhdr->buddy);
 848                         zhdr->cpu = -1;
 849                         set_bit(UNDER_RECLAIM, &page->private);
 850                         break;
 851                 }
 852
 853                 list_del_init(&page->lru);
 854                 spin_unlock(&pool->lock);
 855
 856                 if (!test_bit(PAGE_HEADLESS, &page->private)) {
 857                         /*
 858                          * We need encode the handles before unlocking, since
 859                          * we can race with free that will set
 860                          * (first|last)_chunks to 0
 861                          */
 862                         first_handle = 0;
 863                         last_handle = 0;
 864                         middle_handle = 0;
 865                         if (zhdr->first_chunks)
 866                                 first_handle = encode_handle(zhdr, FIRST);
 867                         if (zhdr->middle_chunks)
 868                                 middle_handle = encode_handle(zhdr, MIDDLE);
 869                         if (zhdr->last_chunks)
 870                                 last_handle = encode_handle(zhdr, LAST);
 871                         /*
 872                          * it's safe to unlock here because we hold a
 873                          * reference to this page
 874                          */
 875                         z3fold_page_unlock(zhdr);
 876                 } else {
 877                         first_handle = encode_handle(zhdr, HEADLESS);
 878                         last_handle = middle_handle = 0;
 879                 }
 880
 881                 /* Issue the eviction callback(s) */
 882                 if (middle_handle) {
 883                         ret = pool->ops->evict(pool, middle_handle);
 884                         if (ret)
 885                                 goto next;
 886                 }
 887                 if (first_handle) {
 888                         ret = pool->ops->evict(pool, first_handle);
 889                         if (ret)
 890                                 goto next;
 891                 }
 892                 if (last_handle) {
 893                         ret = pool->ops->evict(pool, last_handle);
 894                         if (ret)
 895                                 goto next;
 896                 }
 897 next:
 898                 if (test_bit(PAGE_HEADLESS, &page->private)) {
 899                         if (ret == 0) {
 900                                 free_z3fold_page(page);
 901                                 return 0;
 902                         }
 903                         spin_lock(&pool->lock);
 904                         list_add(&page->lru, &pool->lru);
 905                         spin_unlock(&pool->lock);
 906                 } else {
 907                         z3fold_page_lock(zhdr);
 908                         clear_bit(UNDER_RECLAIM, &page->private);
 909                         if (kref_put(&zhdr->refcount,
 910                                         release_z3fold_page_locked)) {
 911                                 atomic64_dec(&pool->pages_nr);
 912                                 return 0;
 913                         }
 914                         /*
 915                          * if we are here, the page is still not completely
 916                          * free. Take the global pool lock then to be able
 917                          * to add it back to the lru list
 918                          */
 919                         spin_lock(&pool->lock);
 920                         list_add(&page->lru, &pool->lru);
 921                         spin_unlock(&pool->lock);
 922                         z3fold_page_unlock(zhdr);
 923                 }
 924
 925                 /* We started off locked to we need to lock the pool back */
 926                 spin_lock(&pool->lock);
 927         }
 928         spin_unlock(&pool->lock);
 929         return -EAGAIN;
 930 }
 931
 932 /**
 933  * z3fold_map() - maps the allocation associated with the given handle
 934  * @pool:       pool in which the allocation resides
 935  * @handle:     handle associated with the allocation to be mapped
 936  *
 937  * Extracts the buddy number from handle and constructs the pointer to the
 938  * correct starting chunk within the page.
 939  *
 940  * Returns: a pointer to the mapped allocation
 941  */
 942 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
 943 {
 944         struct z3fold_header *zhdr;
 945         struct page *page;
 946         void *addr;
 947         enum buddy buddy;
 948
 949         zhdr = handle_to_z3fold_header(handle);
 950         addr = zhdr;
 951         page = virt_to_page(zhdr);
 952
 953         if (test_bit(PAGE_HEADLESS, &page->private))
 954                 goto out;
 955
 956         z3fold_page_lock(zhdr);
 957         buddy = handle_to_buddy(handle);
 958         switch (buddy) {
 959         case FIRST:
 960                 addr += ZHDR_SIZE_ALIGNED;
 961                 break;
 962         case MIDDLE:
 963                 addr += zhdr->start_middle << CHUNK_SHIFT;
 964                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 965                 break;
 966         case LAST:
 967                 addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
 968                 break;
 969         default:
 970                 pr_err("unknown buddy id %d\n", buddy);
 971                 WARN_ON(1);
 972                 addr = NULL;
 973                 break;
 974         }
 975
 976         z3fold_page_unlock(zhdr);
 977 out:
 978         return addr;
 979 }
 980
 981 /**
 982  * z3fold_unmap() - unmaps the allocation associated with the given handle
 983  * @pool:       pool in which the allocation resides
 984  * @handle:     handle associated with the allocation to be unmapped
 985  */
 986 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
 987 {
 988         struct z3fold_header *zhdr;
 989         struct page *page;
 990         enum buddy buddy;
 991
 992         zhdr = handle_to_z3fold_header(handle);
 993         page = virt_to_page(zhdr);
 994
 995         if (test_bit(PAGE_HEADLESS, &page->private))
 996                 return;
 997
 998         z3fold_page_lock(zhdr);
 999         buddy = handle_to_buddy(handle);
1000         if (buddy == MIDDLE)
1001                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1002         z3fold_page_unlock(zhdr);
1003 }
1004
1005 /**
1006  * z3fold_get_pool_size() - gets the z3fold pool size in pages
1007  * @pool:       pool whose size is being queried
1008  *
1009  * Returns: size in pages of the given pool.
1010  */
1011 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
1012 {
1013         return atomic64_read(&pool->pages_nr);
1014 }
1015
1016 /*****************
1017  * zpool
1018  ****************/
1019
1020 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
1021 {
1022         if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
1023                 return pool->zpool_ops->evict(pool->zpool, handle);
1024         else
1025                 return -ENOENT;
1026 }
1027
1028 static const struct z3fold_ops z3fold_zpool_ops = {
1029         .evict =        z3fold_zpool_evict
1030 };
1031
1032 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
1033                                const struct zpool_ops *zpool_ops,
1034                                struct zpool *zpool)
1035 {
1036         struct z3fold_pool *pool;
1037
1038         pool = z3fold_create_pool(name, gfp,
1039                                 zpool_ops ? &z3fold_zpool_ops : NULL);
1040         if (pool) {
1041                 pool->zpool = zpool;
1042                 pool->zpool_ops = zpool_ops;
1043         }
1044         return pool;
1045 }
1046
1047 static void z3fold_zpool_destroy(void *pool)
1048 {
1049         z3fold_destroy_pool(pool);
1050 }
1051
1052 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1053                         unsigned long *handle)
1054 {
1055         return z3fold_alloc(pool, size, gfp, handle);
1056 }
1057 static void z3fold_zpool_free(void *pool, unsigned long handle)
1058 {
1059         z3fold_free(pool, handle);
1060 }
1061
1062 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
1063                         unsigned int *reclaimed)
1064 {
1065         unsigned int total = 0;
1066         int ret = -EINVAL;
1067
1068         while (total < pages) {
1069                 ret = z3fold_reclaim_page(pool, 8);
1070                 if (ret < 0)
1071                         break;
1072                 total++;
1073         }
1074
1075         if (reclaimed)
1076                 *reclaimed = total;
1077
1078         return ret;
1079 }
1080
1081 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1082                         enum zpool_mapmode mm)
1083 {
1084         return z3fold_map(pool, handle);
1085 }
1086 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1087 {
1088         z3fold_unmap(pool, handle);
1089 }
1090
1091 static u64 z3fold_zpool_total_size(void *pool)
1092 {
1093         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1094 }
1095
1096 static struct zpool_driver z3fold_zpool_driver = {
1097         .type =         "z3fold",
1098         .owner =        THIS_MODULE,
1099         .create =       z3fold_zpool_create,
1100         .destroy =      z3fold_zpool_destroy,
1101         .malloc =       z3fold_zpool_malloc,
1102         .free =         z3fold_zpool_free,
1103         .shrink =       z3fold_zpool_shrink,
1104         .map =          z3fold_zpool_map,
1105         .unmap =        z3fold_zpool_unmap,
1106         .total_size =   z3fold_zpool_total_size,
1107 };
1108
1109 MODULE_ALIAS("zpool-z3fold");
1110
1111 static int __init init_z3fold(void)
1112 {
1113         /* Make sure the z3fold header is not larger than the page size */
1114         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
1115         zpool_register_driver(&z3fold_zpool_driver);
1116
1117         return 0;
1118 }
1119
1120 static void __exit exit_z3fold(void)
1121 {
1122         zpool_unregister_driver(&z3fold_zpool_driver);
1123 }
1124
1125 module_init(init_z3fold);
1126 module_exit(exit_z3fold);
1127
1128 MODULE_LICENSE("GPL");
1129 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1130 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");