mm/z3fold.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * z3fold.c
   4  *
   5  * Author: Vitaly Wool <vitaly.wool@konsulko.com>
   6  * Copyright (C) 2016, Sony Mobile Communications Inc.
   7  *
   8  * This implementation is based on zbud written by Seth Jennings.
   9  *
  10  * z3fold is an special purpose allocator for storing compressed pages. It
  11  * can store up to three compressed pages per page which improves the
  12  * compression ratio of zbud while retaining its main concepts (e. g. always
  13  * storing an integral number of objects per page) and simplicity.
  14  * It still has simple and deterministic reclaim properties that make it
  15  * preferable to a higher density approach (with no requirement on integral
  16  * number of object per page) when reclaim is used.
  17  *
  18  * As in zbud, pages are divided into "chunks".  The size of the chunks is
  19  * fixed at compile time and is determined by NCHUNKS_ORDER below.
  20  *
  21  * z3fold doesn't export any API and is meant to be used via zpool API.
  22  */
  23
  24 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  25
  26 #include <linux/atomic.h>
  27 #include <linux/sched.h>
  28 #include <linux/cpumask.h>
  29 #include <linux/list.h>
  30 #include <linux/mm.h>
  31 #include <linux/module.h>
  32 #include <linux/page-flags.h>
  33 #include <linux/migrate.h>
  34 #include <linux/node.h>
  35 #include <linux/compaction.h>
  36 #include <linux/percpu.h>
  37 #include <linux/preempt.h>
  38 #include <linux/workqueue.h>
  39 #include <linux/slab.h>
  40 #include <linux/spinlock.h>
  41 #include <linux/zpool.h>
  42 #include <linux/kmemleak.h>
  43
  44 /*
  45  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
  46  * adjusting internal fragmentation.  It also determines the number of
  47  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
  48  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
  49  * in the beginning of an allocated page are occupied by z3fold header, so
  50  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
  51  * which shows the max number of free chunks in z3fold page, also there will
  52  * be 63, or 62, respectively, freelists per pool.
  53  */
  54 #define NCHUNKS_ORDER   6
  55
  56 #define CHUNK_SHIFT     (PAGE_SHIFT - NCHUNKS_ORDER)
  57 #define CHUNK_SIZE      (1 << CHUNK_SHIFT)
  58 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
  59 #define ZHDR_CHUNKS     (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
  60 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
  61 #define NCHUNKS         (TOTAL_CHUNKS - ZHDR_CHUNKS)
  62
  63 #define BUDDY_MASK      (0x3)
  64 #define BUDDY_SHIFT     2
  65 #define SLOTS_ALIGN     (0x40)
  66
  67 /*****************
  68  * Structures
  69 *****************/
  70 struct z3fold_pool;
  71
  72 enum buddy {
  73         HEADLESS = 0,
  74         FIRST,
  75         MIDDLE,
  76         LAST,
  77         BUDDIES_MAX = LAST
  78 };
  79
  80 struct z3fold_buddy_slots {
  81         /*
  82          * we are using BUDDY_MASK in handle_to_buddy etc. so there should
  83          * be enough slots to hold all possible variants
  84          */
  85         unsigned long slot[BUDDY_MASK + 1];
  86         unsigned long pool; /* back link */
  87         rwlock_t lock;
  88 };
  89 #define HANDLE_FLAG_MASK        (0x03)
  90
  91 /*
  92  * struct z3fold_header - z3fold page metadata occupying first chunks of each
  93  *                      z3fold page, except for HEADLESS pages
  94  * @buddy:              links the z3fold page into the relevant list in the
  95  *                      pool
  96  * @page_lock:          per-page lock
  97  * @refcount:           reference count for the z3fold page
  98  * @work:               work_struct for page layout optimization
  99  * @slots:              pointer to the structure holding buddy slots
 100  * @pool:               pointer to the containing pool
 101  * @cpu:                CPU which this page "belongs" to
 102  * @first_chunks:       the size of the first buddy in chunks, 0 if free
 103  * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
 104  * @last_chunks:        the size of the last buddy in chunks, 0 if free
 105  * @first_num:          the starting number (for the first handle)
 106  * @mapped_count:       the number of objects currently mapped
 107  */
 108 struct z3fold_header {
 109         struct list_head buddy;
 110         spinlock_t page_lock;
 111         struct kref refcount;
 112         struct work_struct work;
 113         struct z3fold_buddy_slots *slots;
 114         struct z3fold_pool *pool;
 115         short cpu;
 116         unsigned short first_chunks;
 117         unsigned short middle_chunks;
 118         unsigned short last_chunks;
 119         unsigned short start_middle;
 120         unsigned short first_num:2;
 121         unsigned short mapped_count:2;
 122         unsigned short foreign_handles:2;
 123 };
 124
 125 /**
 126  * struct z3fold_pool - stores metadata for each z3fold pool
 127  * @name:       pool name
 128  * @lock:       protects pool unbuddied lists
 129  * @stale_lock: protects pool stale page list
 130  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
 131  *              buddies; the list each z3fold page is added to depends on
 132  *              the size of its free region.
 133  * @stale:      list of pages marked for freeing
 134  * @pages_nr:   number of z3fold pages in the pool.
 135  * @c_handle:   cache for z3fold_buddy_slots allocation
 136  * @compact_wq: workqueue for page layout background optimization
 137  * @release_wq: workqueue for safe page release
 138  * @work:       work_struct for safe page release
 139  *
 140  * This structure is allocated at pool creation time and maintains metadata
 141  * pertaining to a particular z3fold pool.
 142  */
 143 struct z3fold_pool {
 144         const char *name;
 145         spinlock_t lock;
 146         spinlock_t stale_lock;
 147         struct list_head *unbuddied;
 148         struct list_head stale;
 149         atomic64_t pages_nr;
 150         struct kmem_cache *c_handle;
 151         struct workqueue_struct *compact_wq;
 152         struct workqueue_struct *release_wq;
 153         struct work_struct work;
 154 };
 155
 156 /*
 157  * Internal z3fold page flags
 158  */
 159 enum z3fold_page_flags {
 160         PAGE_HEADLESS = 0,
 161         MIDDLE_CHUNK_MAPPED,
 162         NEEDS_COMPACTING,
 163         PAGE_STALE,
 164         PAGE_CLAIMED, /* by either reclaim or free */
 165         PAGE_MIGRATED, /* page is migrated and soon to be released */
 166 };
 167
 168 /*
 169  * handle flags, go under HANDLE_FLAG_MASK
 170  */
 171 enum z3fold_handle_flags {
 172         HANDLES_NOFREE = 0,
 173 };
 174
 175 /*
 176  * Forward declarations
 177  */
 178 static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool);
 179 static void compact_page_work(struct work_struct *w);
 180
 181 /*****************
 182  * Helpers
 183 *****************/
 184
 185 /* Converts an allocation size in bytes to size in z3fold chunks */
 186 static int size_to_chunks(size_t size)
 187 {
 188         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 189 }
 190
 191 #define for_each_unbuddied_list(_iter, _begin) \
 192         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 193
 194 static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
 195                                                         gfp_t gfp)
 196 {
 197         struct z3fold_buddy_slots *slots = kmem_cache_zalloc(pool->c_handle,
 198                                                              gfp);
 199
 200         if (slots) {
 201                 /* It will be freed separately in free_handle(). */
 202                 kmemleak_not_leak(slots);
 203                 slots->pool = (unsigned long)pool;
 204                 rwlock_init(&slots->lock);
 205         }
 206
 207         return slots;
 208 }
 209
 210 static inline struct z3fold_pool *slots_to_pool(struct z3fold_buddy_slots *s)
 211 {
 212         return (struct z3fold_pool *)(s->pool & ~HANDLE_FLAG_MASK);
 213 }
 214
 215 static inline struct z3fold_buddy_slots *handle_to_slots(unsigned long handle)
 216 {
 217         return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
 218 }
 219
 220 /* Lock a z3fold page */
 221 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 222 {
 223         spin_lock(&zhdr->page_lock);
 224 }
 225
 226 /* Try to lock a z3fold page */
 227 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 228 {
 229         return spin_trylock(&zhdr->page_lock);
 230 }
 231
 232 /* Unlock a z3fold page */
 233 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 234 {
 235         spin_unlock(&zhdr->page_lock);
 236 }
 237
 238 /* return locked z3fold page if it's not headless */
 239 static inline struct z3fold_header *get_z3fold_header(unsigned long handle)
 240 {
 241         struct z3fold_buddy_slots *slots;
 242         struct z3fold_header *zhdr;
 243         int locked = 0;
 244
 245         if (!(handle & (1 << PAGE_HEADLESS))) {
 246                 slots = handle_to_slots(handle);
 247                 do {
 248                         unsigned long addr;
 249
 250                         read_lock(&slots->lock);
 251                         addr = *(unsigned long *)handle;
 252                         zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 253                         locked = z3fold_page_trylock(zhdr);
 254                         read_unlock(&slots->lock);
 255                         if (locked) {
 256                                 struct page *page = virt_to_page(zhdr);
 257
 258                                 if (!test_bit(PAGE_MIGRATED, &page->private))
 259                                         break;
 260                                 z3fold_page_unlock(zhdr);
 261                         }
 262                         cpu_relax();
 263                 } while (true);
 264         } else {
 265                 zhdr = (struct z3fold_header *)(handle & PAGE_MASK);
 266         }
 267
 268         return zhdr;
 269 }
 270
 271 static inline void put_z3fold_header(struct z3fold_header *zhdr)
 272 {
 273         struct page *page = virt_to_page(zhdr);
 274
 275         if (!test_bit(PAGE_HEADLESS, &page->private))
 276                 z3fold_page_unlock(zhdr);
 277 }
 278
 279 static inline void free_handle(unsigned long handle, struct z3fold_header *zhdr)
 280 {
 281         struct z3fold_buddy_slots *slots;
 282         int i;
 283         bool is_free;
 284
 285         if (WARN_ON(*(unsigned long *)handle == 0))
 286                 return;
 287
 288         slots = handle_to_slots(handle);
 289         write_lock(&slots->lock);
 290         *(unsigned long *)handle = 0;
 291
 292         if (test_bit(HANDLES_NOFREE, &slots->pool)) {
 293                 write_unlock(&slots->lock);
 294                 return; /* simple case, nothing else to do */
 295         }
 296
 297         if (zhdr->slots != slots)
 298                 zhdr->foreign_handles--;
 299
 300         is_free = true;
 301         for (i = 0; i <= BUDDY_MASK; i++) {
 302                 if (slots->slot[i]) {
 303                         is_free = false;
 304                         break;
 305                 }
 306         }
 307         write_unlock(&slots->lock);
 308
 309         if (is_free) {
 310                 struct z3fold_pool *pool = slots_to_pool(slots);
 311
 312                 if (zhdr->slots == slots)
 313                         zhdr->slots = NULL;
 314                 kmem_cache_free(pool->c_handle, slots);
 315         }
 316 }
 317
 318 /* Initializes the z3fold header of a newly allocated z3fold page */
 319 static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
 320                                         struct z3fold_pool *pool, gfp_t gfp)
 321 {
 322         struct z3fold_header *zhdr = page_address(page);
 323         struct z3fold_buddy_slots *slots;
 324
 325         clear_bit(PAGE_HEADLESS, &page->private);
 326         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 327         clear_bit(NEEDS_COMPACTING, &page->private);
 328         clear_bit(PAGE_STALE, &page->private);
 329         clear_bit(PAGE_CLAIMED, &page->private);
 330         clear_bit(PAGE_MIGRATED, &page->private);
 331         if (headless)
 332                 return zhdr;
 333
 334         slots = alloc_slots(pool, gfp);
 335         if (!slots)
 336                 return NULL;
 337
 338         memset(zhdr, 0, sizeof(*zhdr));
 339         spin_lock_init(&zhdr->page_lock);
 340         kref_init(&zhdr->refcount);
 341         zhdr->cpu = -1;
 342         zhdr->slots = slots;
 343         zhdr->pool = pool;
 344         INIT_LIST_HEAD(&zhdr->buddy);
 345         INIT_WORK(&zhdr->work, compact_page_work);
 346         return zhdr;
 347 }
 348
 349 /* Resets the struct page fields and frees the page */
 350 static void free_z3fold_page(struct page *page, bool headless)
 351 {
 352         if (!headless) {
 353                 lock_page(page);
 354                 __ClearPageMovable(page);
 355                 unlock_page(page);
 356         }
 357         __free_page(page);
 358 }
 359
 360 /* Helper function to build the index */
 361 static inline int __idx(struct z3fold_header *zhdr, enum buddy bud)
 362 {
 363         return (bud + zhdr->first_num) & BUDDY_MASK;
 364 }
 365
 366 /*
 367  * Encodes the handle of a particular buddy within a z3fold page.
 368  * Zhdr->page_lock should be held as this function accesses first_num
 369  * if bud != HEADLESS.
 370  */
 371 static unsigned long __encode_handle(struct z3fold_header *zhdr,
 372                                 struct z3fold_buddy_slots *slots,
 373                                 enum buddy bud)
 374 {
 375         unsigned long h = (unsigned long)zhdr;
 376         int idx = 0;
 377
 378         /*
 379          * For a headless page, its handle is its pointer with the extra
 380          * PAGE_HEADLESS bit set
 381          */
 382         if (bud == HEADLESS)
 383                 return h | (1 << PAGE_HEADLESS);
 384
 385         /* otherwise, return pointer to encoded handle */
 386         idx = __idx(zhdr, bud);
 387         h += idx;
 388         if (bud == LAST)
 389                 h |= (zhdr->last_chunks << BUDDY_SHIFT);
 390
 391         write_lock(&slots->lock);
 392         slots->slot[idx] = h;
 393         write_unlock(&slots->lock);
 394         return (unsigned long)&slots->slot[idx];
 395 }
 396
 397 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 398 {
 399         return __encode_handle(zhdr, zhdr->slots, bud);
 400 }
 401
 402 /* only for LAST bud, returns zero otherwise */
 403 static unsigned short handle_to_chunks(unsigned long handle)
 404 {
 405         struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 406         unsigned long addr;
 407
 408         read_lock(&slots->lock);
 409         addr = *(unsigned long *)handle;
 410         read_unlock(&slots->lock);
 411         return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 412 }
 413
 414 /*
 415  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
 416  *  but that doesn't matter. because the masking will result in the
 417  *  correct buddy number.
 418  */
 419 static enum buddy handle_to_buddy(unsigned long handle)
 420 {
 421         struct z3fold_header *zhdr;
 422         struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 423         unsigned long addr;
 424
 425         read_lock(&slots->lock);
 426         WARN_ON(handle & (1 << PAGE_HEADLESS));
 427         addr = *(unsigned long *)handle;
 428         read_unlock(&slots->lock);
 429         zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 430         return (addr - zhdr->first_num) & BUDDY_MASK;
 431 }
 432
 433 static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
 434 {
 435         return zhdr->pool;
 436 }
 437
 438 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 439 {
 440         struct page *page = virt_to_page(zhdr);
 441         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 442
 443         WARN_ON(!list_empty(&zhdr->buddy));
 444         set_bit(PAGE_STALE, &page->private);
 445         clear_bit(NEEDS_COMPACTING, &page->private);
 446         spin_lock(&pool->lock);
 447         spin_unlock(&pool->lock);
 448
 449         if (locked)
 450                 z3fold_page_unlock(zhdr);
 451
 452         spin_lock(&pool->stale_lock);
 453         list_add(&zhdr->buddy, &pool->stale);
 454         queue_work(pool->release_wq, &pool->work);
 455         spin_unlock(&pool->stale_lock);
 456
 457         atomic64_dec(&pool->pages_nr);
 458 }
 459
 460 static void release_z3fold_page_locked(struct kref *ref)
 461 {
 462         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 463                                                 refcount);
 464         WARN_ON(z3fold_page_trylock(zhdr));
 465         __release_z3fold_page(zhdr, true);
 466 }
 467
 468 static void release_z3fold_page_locked_list(struct kref *ref)
 469 {
 470         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 471                                                refcount);
 472         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 473
 474         spin_lock(&pool->lock);
 475         list_del_init(&zhdr->buddy);
 476         spin_unlock(&pool->lock);
 477
 478         WARN_ON(z3fold_page_trylock(zhdr));
 479         __release_z3fold_page(zhdr, true);
 480 }
 481
 482 static inline int put_z3fold_locked(struct z3fold_header *zhdr)
 483 {
 484         return kref_put(&zhdr->refcount, release_z3fold_page_locked);
 485 }
 486
 487 static inline int put_z3fold_locked_list(struct z3fold_header *zhdr)
 488 {
 489         return kref_put(&zhdr->refcount, release_z3fold_page_locked_list);
 490 }
 491
 492 static void free_pages_work(struct work_struct *w)
 493 {
 494         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 495
 496         spin_lock(&pool->stale_lock);
 497         while (!list_empty(&pool->stale)) {
 498                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
 499                                                 struct z3fold_header, buddy);
 500                 struct page *page = virt_to_page(zhdr);
 501
 502                 list_del(&zhdr->buddy);
 503                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
 504                         continue;
 505                 spin_unlock(&pool->stale_lock);
 506                 cancel_work_sync(&zhdr->work);
 507                 free_z3fold_page(page, false);
 508                 cond_resched();
 509                 spin_lock(&pool->stale_lock);
 510         }
 511         spin_unlock(&pool->stale_lock);
 512 }
 513
 514 /*
 515  * Returns the number of free chunks in a z3fold page.
 516  * NB: can't be used with HEADLESS pages.
 517  */
 518 static int num_free_chunks(struct z3fold_header *zhdr)
 519 {
 520         int nfree;
 521         /*
 522          * If there is a middle object, pick up the bigger free space
 523          * either before or after it. Otherwise just subtract the number
 524          * of chunks occupied by the first and the last objects.
 525          */
 526         if (zhdr->middle_chunks != 0) {
 527                 int nfree_before = zhdr->first_chunks ?
 528                         0 : zhdr->start_middle - ZHDR_CHUNKS;
 529                 int nfree_after = zhdr->last_chunks ?
 530                         0 : TOTAL_CHUNKS -
 531                                 (zhdr->start_middle + zhdr->middle_chunks);
 532                 nfree = max(nfree_before, nfree_after);
 533         } else
 534                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
 535         return nfree;
 536 }
 537
 538 /* Add to the appropriate unbuddied list */
 539 static inline void add_to_unbuddied(struct z3fold_pool *pool,
 540                                 struct z3fold_header *zhdr)
 541 {
 542         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 543                         zhdr->middle_chunks == 0) {
 544                 struct list_head *unbuddied;
 545                 int freechunks = num_free_chunks(zhdr);
 546
 547                 migrate_disable();
 548                 unbuddied = this_cpu_ptr(pool->unbuddied);
 549                 spin_lock(&pool->lock);
 550                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
 551                 spin_unlock(&pool->lock);
 552                 zhdr->cpu = smp_processor_id();
 553                 migrate_enable();
 554         }
 555 }
 556
 557 static inline enum buddy get_free_buddy(struct z3fold_header *zhdr, int chunks)
 558 {
 559         enum buddy bud = HEADLESS;
 560
 561         if (zhdr->middle_chunks) {
 562                 if (!zhdr->first_chunks &&
 563                     chunks <= zhdr->start_middle - ZHDR_CHUNKS)
 564                         bud = FIRST;
 565                 else if (!zhdr->last_chunks)
 566                         bud = LAST;
 567         } else {
 568                 if (!zhdr->first_chunks)
 569                         bud = FIRST;
 570                 else if (!zhdr->last_chunks)
 571                         bud = LAST;
 572                 else
 573                         bud = MIDDLE;
 574         }
 575
 576         return bud;
 577 }
 578
 579 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 580                                 unsigned short dst_chunk)
 581 {
 582         void *beg = zhdr;
 583         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
 584                        beg + (zhdr->start_middle << CHUNK_SHIFT),
 585                        zhdr->middle_chunks << CHUNK_SHIFT);
 586 }
 587
 588 static inline bool buddy_single(struct z3fold_header *zhdr)
 589 {
 590         return !((zhdr->first_chunks && zhdr->middle_chunks) ||
 591                         (zhdr->first_chunks && zhdr->last_chunks) ||
 592                         (zhdr->middle_chunks && zhdr->last_chunks));
 593 }
 594
 595 static struct z3fold_header *compact_single_buddy(struct z3fold_header *zhdr)
 596 {
 597         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 598         void *p = zhdr;
 599         unsigned long old_handle = 0;
 600         size_t sz = 0;
 601         struct z3fold_header *new_zhdr = NULL;
 602         int first_idx = __idx(zhdr, FIRST);
 603         int middle_idx = __idx(zhdr, MIDDLE);
 604         int last_idx = __idx(zhdr, LAST);
 605         unsigned short *moved_chunks = NULL;
 606
 607         /*
 608          * No need to protect slots here -- all the slots are "local" and
 609          * the page lock is already taken
 610          */
 611         if (zhdr->first_chunks && zhdr->slots->slot[first_idx]) {
 612                 p += ZHDR_SIZE_ALIGNED;
 613                 sz = zhdr->first_chunks << CHUNK_SHIFT;
 614                 old_handle = (unsigned long)&zhdr->slots->slot[first_idx];
 615                 moved_chunks = &zhdr->first_chunks;
 616         } else if (zhdr->middle_chunks && zhdr->slots->slot[middle_idx]) {
 617                 p += zhdr->start_middle << CHUNK_SHIFT;
 618                 sz = zhdr->middle_chunks << CHUNK_SHIFT;
 619                 old_handle = (unsigned long)&zhdr->slots->slot[middle_idx];
 620                 moved_chunks = &zhdr->middle_chunks;
 621         } else if (zhdr->last_chunks && zhdr->slots->slot[last_idx]) {
 622                 p += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
 623                 sz = zhdr->last_chunks << CHUNK_SHIFT;
 624                 old_handle = (unsigned long)&zhdr->slots->slot[last_idx];
 625                 moved_chunks = &zhdr->last_chunks;
 626         }
 627
 628         if (sz > 0) {
 629                 enum buddy new_bud = HEADLESS;
 630                 short chunks = size_to_chunks(sz);
 631                 void *q;
 632
 633                 new_zhdr = __z3fold_alloc(pool, sz, false);
 634                 if (!new_zhdr)
 635                         return NULL;
 636
 637                 if (WARN_ON(new_zhdr == zhdr))
 638                         goto out_fail;
 639
 640                 new_bud = get_free_buddy(new_zhdr, chunks);
 641                 q = new_zhdr;
 642                 switch (new_bud) {
 643                 case FIRST:
 644                         new_zhdr->first_chunks = chunks;
 645                         q += ZHDR_SIZE_ALIGNED;
 646                         break;
 647                 case MIDDLE:
 648                         new_zhdr->middle_chunks = chunks;
 649                         new_zhdr->start_middle =
 650                                 new_zhdr->first_chunks + ZHDR_CHUNKS;
 651                         q += new_zhdr->start_middle << CHUNK_SHIFT;
 652                         break;
 653                 case LAST:
 654                         new_zhdr->last_chunks = chunks;
 655                         q += PAGE_SIZE - (new_zhdr->last_chunks << CHUNK_SHIFT);
 656                         break;
 657                 default:
 658                         goto out_fail;
 659                 }
 660                 new_zhdr->foreign_handles++;
 661                 memcpy(q, p, sz);
 662                 write_lock(&zhdr->slots->lock);
 663                 *(unsigned long *)old_handle = (unsigned long)new_zhdr +
 664                         __idx(new_zhdr, new_bud);
 665                 if (new_bud == LAST)
 666                         *(unsigned long *)old_handle |=
 667                                         (new_zhdr->last_chunks << BUDDY_SHIFT);
 668                 write_unlock(&zhdr->slots->lock);
 669                 add_to_unbuddied(pool, new_zhdr);
 670                 z3fold_page_unlock(new_zhdr);
 671
 672                 *moved_chunks = 0;
 673         }
 674
 675         return new_zhdr;
 676
 677 out_fail:
 678         if (new_zhdr && !put_z3fold_locked(new_zhdr)) {
 679                 add_to_unbuddied(pool, new_zhdr);
 680                 z3fold_page_unlock(new_zhdr);
 681         }
 682         return NULL;
 683
 684 }
 685
 686 #define BIG_CHUNK_GAP   3
 687 /* Has to be called with lock held */
 688 static int z3fold_compact_page(struct z3fold_header *zhdr)
 689 {
 690         struct page *page = virt_to_page(zhdr);
 691
 692         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 693                 return 0; /* can't move middle chunk, it's used */
 694
 695         if (unlikely(PageIsolated(page)))
 696                 return 0;
 697
 698         if (zhdr->middle_chunks == 0)
 699                 return 0; /* nothing to compact */
 700
 701         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
 702                 /* move to the beginning */
 703                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
 704                 zhdr->first_chunks = zhdr->middle_chunks;
 705                 zhdr->middle_chunks = 0;
 706                 zhdr->start_middle = 0;
 707                 zhdr->first_num++;
 708                 return 1;
 709         }
 710
 711         /*
 712          * moving data is expensive, so let's only do that if
 713          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
 714          */
 715         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
 716             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
 717                         BIG_CHUNK_GAP) {
 718                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
 719                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 720                 return 1;
 721         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
 722                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
 723                                         + zhdr->middle_chunks) >=
 724                         BIG_CHUNK_GAP) {
 725                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
 726                         zhdr->middle_chunks;
 727                 mchunk_memmove(zhdr, new_start);
 728                 zhdr->start_middle = new_start;
 729                 return 1;
 730         }
 731
 732         return 0;
 733 }
 734
 735 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 736 {
 737         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 738         struct page *page;
 739
 740         page = virt_to_page(zhdr);
 741         if (locked)
 742                 WARN_ON(z3fold_page_trylock(zhdr));
 743         else
 744                 z3fold_page_lock(zhdr);
 745         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
 746                 z3fold_page_unlock(zhdr);
 747                 return;
 748         }
 749         spin_lock(&pool->lock);
 750         list_del_init(&zhdr->buddy);
 751         spin_unlock(&pool->lock);
 752
 753         if (put_z3fold_locked(zhdr))
 754                 return;
 755
 756         if (test_bit(PAGE_STALE, &page->private) ||
 757             test_and_set_bit(PAGE_CLAIMED, &page->private)) {
 758                 z3fold_page_unlock(zhdr);
 759                 return;
 760         }
 761
 762         if (!zhdr->foreign_handles && buddy_single(zhdr) &&
 763             zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) {
 764                 if (!put_z3fold_locked(zhdr)) {
 765                         clear_bit(PAGE_CLAIMED, &page->private);
 766                         z3fold_page_unlock(zhdr);
 767                 }
 768                 return;
 769         }
 770
 771         z3fold_compact_page(zhdr);
 772         add_to_unbuddied(pool, zhdr);
 773         clear_bit(PAGE_CLAIMED, &page->private);
 774         z3fold_page_unlock(zhdr);
 775 }
 776
 777 static void compact_page_work(struct work_struct *w)
 778 {
 779         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
 780                                                 work);
 781
 782         do_compact_page(zhdr, false);
 783 }
 784
 785 /* returns _locked_ z3fold page header or NULL */
 786 static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
 787                                                 size_t size, bool can_sleep)
 788 {
 789         struct z3fold_header *zhdr = NULL;
 790         struct page *page;
 791         struct list_head *unbuddied;
 792         int chunks = size_to_chunks(size), i;
 793
 794 lookup:
 795         migrate_disable();
 796         /* First, try to find an unbuddied z3fold page. */
 797         unbuddied = this_cpu_ptr(pool->unbuddied);
 798         for_each_unbuddied_list(i, chunks) {
 799                 struct list_head *l = &unbuddied[i];
 800
 801                 zhdr = list_first_entry_or_null(READ_ONCE(l),
 802                                         struct z3fold_header, buddy);
 803
 804                 if (!zhdr)
 805                         continue;
 806
 807                 /* Re-check under lock. */
 808                 spin_lock(&pool->lock);
 809                 if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
 810                                                 struct z3fold_header, buddy)) ||
 811                     !z3fold_page_trylock(zhdr)) {
 812                         spin_unlock(&pool->lock);
 813                         zhdr = NULL;
 814                         migrate_enable();
 815                         if (can_sleep)
 816                                 cond_resched();
 817                         goto lookup;
 818                 }
 819                 list_del_init(&zhdr->buddy);
 820                 zhdr->cpu = -1;
 821                 spin_unlock(&pool->lock);
 822
 823                 page = virt_to_page(zhdr);
 824                 if (test_bit(NEEDS_COMPACTING, &page->private) ||
 825                     test_bit(PAGE_CLAIMED, &page->private)) {
 826                         z3fold_page_unlock(zhdr);
 827                         zhdr = NULL;
 828                         migrate_enable();
 829                         if (can_sleep)
 830                                 cond_resched();
 831                         goto lookup;
 832                 }
 833
 834                 /*
 835                  * this page could not be removed from its unbuddied
 836                  * list while pool lock was held, and then we've taken
 837                  * page lock so kref_put could not be called before
 838                  * we got here, so it's safe to just call kref_get()
 839                  */
 840                 kref_get(&zhdr->refcount);
 841                 break;
 842         }
 843         migrate_enable();
 844
 845         if (!zhdr) {
 846                 int cpu;
 847
 848                 /* look for _exact_ match on other cpus' lists */
 849                 for_each_online_cpu(cpu) {
 850                         struct list_head *l;
 851
 852                         unbuddied = per_cpu_ptr(pool->unbuddied, cpu);
 853                         spin_lock(&pool->lock);
 854                         l = &unbuddied[chunks];
 855
 856                         zhdr = list_first_entry_or_null(READ_ONCE(l),
 857                                                 struct z3fold_header, buddy);
 858
 859                         if (!zhdr || !z3fold_page_trylock(zhdr)) {
 860                                 spin_unlock(&pool->lock);
 861                                 zhdr = NULL;
 862                                 continue;
 863                         }
 864                         list_del_init(&zhdr->buddy);
 865                         zhdr->cpu = -1;
 866                         spin_unlock(&pool->lock);
 867
 868                         page = virt_to_page(zhdr);
 869                         if (test_bit(NEEDS_COMPACTING, &page->private) ||
 870                             test_bit(PAGE_CLAIMED, &page->private)) {
 871                                 z3fold_page_unlock(zhdr);
 872                                 zhdr = NULL;
 873                                 if (can_sleep)
 874                                         cond_resched();
 875                                 continue;
 876                         }
 877                         kref_get(&zhdr->refcount);
 878                         break;
 879                 }
 880         }
 881
 882         if (zhdr && !zhdr->slots) {
 883                 zhdr->slots = alloc_slots(pool, GFP_ATOMIC);
 884                 if (!zhdr->slots)
 885                         goto out_fail;
 886         }
 887         return zhdr;
 888
 889 out_fail:
 890         if (!put_z3fold_locked(zhdr)) {
 891                 add_to_unbuddied(pool, zhdr);
 892                 z3fold_page_unlock(zhdr);
 893         }
 894         return NULL;
 895 }
 896
 897 /*
 898  * API Functions
 899  */
 900
 901 /**
 902  * z3fold_create_pool() - create a new z3fold pool
 903  * @name:       pool name
 904  * @gfp:        gfp flags when allocating the z3fold pool structure
 905  *
 906  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
 907  * failed.
 908  */
 909 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp)
 910 {
 911         struct z3fold_pool *pool = NULL;
 912         int i, cpu;
 913
 914         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
 915         if (!pool)
 916                 goto out;
 917         pool->c_handle = kmem_cache_create("z3fold_handle",
 918                                 sizeof(struct z3fold_buddy_slots),
 919                                 SLOTS_ALIGN, 0, NULL);
 920         if (!pool->c_handle)
 921                 goto out_c;
 922         spin_lock_init(&pool->lock);
 923         spin_lock_init(&pool->stale_lock);
 924         pool->unbuddied = __alloc_percpu(sizeof(struct list_head) * NCHUNKS,
 925                                          __alignof__(struct list_head));
 926         if (!pool->unbuddied)
 927                 goto out_pool;
 928         for_each_possible_cpu(cpu) {
 929                 struct list_head *unbuddied =
 930                                 per_cpu_ptr(pool->unbuddied, cpu);
 931                 for_each_unbuddied_list(i, 0)
 932                         INIT_LIST_HEAD(&unbuddied[i]);
 933         }
 934         INIT_LIST_HEAD(&pool->stale);
 935         atomic64_set(&pool->pages_nr, 0);
 936         pool->name = name;
 937         pool->compact_wq = create_singlethread_workqueue(pool->name);
 938         if (!pool->compact_wq)
 939                 goto out_unbuddied;
 940         pool->release_wq = create_singlethread_workqueue(pool->name);
 941         if (!pool->release_wq)
 942                 goto out_wq;
 943         INIT_WORK(&pool->work, free_pages_work);
 944         return pool;
 945
 946 out_wq:
 947         destroy_workqueue(pool->compact_wq);
 948 out_unbuddied:
 949         free_percpu(pool->unbuddied);
 950 out_pool:
 951         kmem_cache_destroy(pool->c_handle);
 952 out_c:
 953         kfree(pool);
 954 out:
 955         return NULL;
 956 }
 957
 958 /**
 959  * z3fold_destroy_pool() - destroys an existing z3fold pool
 960  * @pool:       the z3fold pool to be destroyed
 961  *
 962  * The pool should be emptied before this function is called.
 963  */
 964 static void z3fold_destroy_pool(struct z3fold_pool *pool)
 965 {
 966         kmem_cache_destroy(pool->c_handle);
 967
 968         /*
 969          * We need to destroy pool->compact_wq before pool->release_wq,
 970          * as any pending work on pool->compact_wq will call
 971          * queue_work(pool->release_wq, &pool->work).
 972          *
 973          * There are still outstanding pages until both workqueues are drained,
 974          * so we cannot unregister migration until then.
 975          */
 976
 977         destroy_workqueue(pool->compact_wq);
 978         destroy_workqueue(pool->release_wq);
 979         free_percpu(pool->unbuddied);
 980         kfree(pool);
 981 }
 982
 983 static const struct movable_operations z3fold_mops;
 984
 985 /**
 986  * z3fold_alloc() - allocates a region of a given size
 987  * @pool:       z3fold pool from which to allocate
 988  * @size:       size in bytes of the desired allocation
 989  * @gfp:        gfp flags used if the pool needs to grow
 990  * @handle:     handle of the new allocation
 991  *
 992  * This function will attempt to find a free region in the pool large enough to
 993  * satisfy the allocation request.  A search of the unbuddied lists is
 994  * performed first. If no suitable free region is found, then a new page is
 995  * allocated and added to the pool to satisfy the request.
 996  *
 997  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
 998  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
 999  * a new page.
1000  */
1001 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
1002                         unsigned long *handle)
1003 {
1004         int chunks = size_to_chunks(size);
1005         struct z3fold_header *zhdr = NULL;
1006         struct page *page = NULL;
1007         enum buddy bud;
1008         bool can_sleep = gfpflags_allow_blocking(gfp);
1009
1010         if (!size || (gfp & __GFP_HIGHMEM))
1011                 return -EINVAL;
1012
1013         if (size > PAGE_SIZE)
1014                 return -ENOSPC;
1015
1016         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
1017                 bud = HEADLESS;
1018         else {
1019 retry:
1020                 zhdr = __z3fold_alloc(pool, size, can_sleep);
1021                 if (zhdr) {
1022                         bud = get_free_buddy(zhdr, chunks);
1023                         if (bud == HEADLESS) {
1024                                 if (!put_z3fold_locked(zhdr))
1025                                         z3fold_page_unlock(zhdr);
1026                                 pr_err("No free chunks in unbuddied\n");
1027                                 WARN_ON(1);
1028                                 goto retry;
1029                         }
1030                         page = virt_to_page(zhdr);
1031                         goto found;
1032                 }
1033                 bud = FIRST;
1034         }
1035
1036         page = alloc_page(gfp);
1037         if (!page)
1038                 return -ENOMEM;
1039
1040         zhdr = init_z3fold_page(page, bud == HEADLESS, pool, gfp);
1041         if (!zhdr) {
1042                 __free_page(page);
1043                 return -ENOMEM;
1044         }
1045         atomic64_inc(&pool->pages_nr);
1046
1047         if (bud == HEADLESS) {
1048                 set_bit(PAGE_HEADLESS, &page->private);
1049                 goto headless;
1050         }
1051         if (can_sleep) {
1052                 lock_page(page);
1053                 __SetPageMovable(page, &z3fold_mops);
1054                 unlock_page(page);
1055         } else {
1056                 WARN_ON(!trylock_page(page));
1057                 __SetPageMovable(page, &z3fold_mops);
1058                 unlock_page(page);
1059         }
1060         z3fold_page_lock(zhdr);
1061
1062 found:
1063         if (bud == FIRST)
1064                 zhdr->first_chunks = chunks;
1065         else if (bud == LAST)
1066                 zhdr->last_chunks = chunks;
1067         else {
1068                 zhdr->middle_chunks = chunks;
1069                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
1070         }
1071         add_to_unbuddied(pool, zhdr);
1072
1073 headless:
1074         spin_lock(&pool->lock);
1075         *handle = encode_handle(zhdr, bud);
1076         spin_unlock(&pool->lock);
1077         if (bud != HEADLESS)
1078                 z3fold_page_unlock(zhdr);
1079
1080         return 0;
1081 }
1082
1083 /**
1084  * z3fold_free() - frees the allocation associated with the given handle
1085  * @pool:       pool in which the allocation resided
1086  * @handle:     handle associated with the allocation returned by z3fold_alloc()
1087  *
1088  * In the case that the z3fold page in which the allocation resides is under
1089  * reclaim, as indicated by the PAGE_CLAIMED flag being set, this function
1090  * only sets the first|middle|last_chunks to 0.  The page is actually freed
1091  * once all buddies are evicted (see z3fold_reclaim_page() below).
1092  */
1093 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
1094 {
1095         struct z3fold_header *zhdr;
1096         struct page *page;
1097         enum buddy bud;
1098         bool page_claimed;
1099
1100         zhdr = get_z3fold_header(handle);
1101         page = virt_to_page(zhdr);
1102         page_claimed = test_and_set_bit(PAGE_CLAIMED, &page->private);
1103
1104         if (test_bit(PAGE_HEADLESS, &page->private)) {
1105                 /* if a headless page is under reclaim, just leave.
1106                  * NB: we use test_and_set_bit for a reason: if the bit
1107                  * has not been set before, we release this page
1108                  * immediately so we don't care about its value any more.
1109                  */
1110                 if (!page_claimed) {
1111                         put_z3fold_header(zhdr);
1112                         free_z3fold_page(page, true);
1113                         atomic64_dec(&pool->pages_nr);
1114                 }
1115                 return;
1116         }
1117
1118         /* Non-headless case */
1119         bud = handle_to_buddy(handle);
1120
1121         switch (bud) {
1122         case FIRST:
1123                 zhdr->first_chunks = 0;
1124                 break;
1125         case MIDDLE:
1126                 zhdr->middle_chunks = 0;
1127                 break;
1128         case LAST:
1129                 zhdr->last_chunks = 0;
1130                 break;
1131         default:
1132                 pr_err("%s: unknown bud %d\n", __func__, bud);
1133                 WARN_ON(1);
1134                 put_z3fold_header(zhdr);
1135                 return;
1136         }
1137
1138         if (!page_claimed)
1139                 free_handle(handle, zhdr);
1140         if (put_z3fold_locked_list(zhdr))
1141                 return;
1142         if (page_claimed) {
1143                 /* the page has not been claimed by us */
1144                 put_z3fold_header(zhdr);
1145                 return;
1146         }
1147         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
1148                 clear_bit(PAGE_CLAIMED, &page->private);
1149                 put_z3fold_header(zhdr);
1150                 return;
1151         }
1152         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
1153                 zhdr->cpu = -1;
1154                 kref_get(&zhdr->refcount);
1155                 clear_bit(PAGE_CLAIMED, &page->private);
1156                 do_compact_page(zhdr, true);
1157                 return;
1158         }
1159         kref_get(&zhdr->refcount);
1160         clear_bit(PAGE_CLAIMED, &page->private);
1161         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
1162         put_z3fold_header(zhdr);
1163 }
1164
1165 /**
1166  * z3fold_map() - maps the allocation associated with the given handle
1167  * @pool:       pool in which the allocation resides
1168  * @handle:     handle associated with the allocation to be mapped
1169  *
1170  * Extracts the buddy number from handle and constructs the pointer to the
1171  * correct starting chunk within the page.
1172  *
1173  * Returns: a pointer to the mapped allocation
1174  */
1175 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
1176 {
1177         struct z3fold_header *zhdr;
1178         struct page *page;
1179         void *addr;
1180         enum buddy buddy;
1181
1182         zhdr = get_z3fold_header(handle);
1183         addr = zhdr;
1184         page = virt_to_page(zhdr);
1185
1186         if (test_bit(PAGE_HEADLESS, &page->private))
1187                 goto out;
1188
1189         buddy = handle_to_buddy(handle);
1190         switch (buddy) {
1191         case FIRST:
1192                 addr += ZHDR_SIZE_ALIGNED;
1193                 break;
1194         case MIDDLE:
1195                 addr += zhdr->start_middle << CHUNK_SHIFT;
1196                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1197                 break;
1198         case LAST:
1199                 addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT);
1200                 break;
1201         default:
1202                 pr_err("unknown buddy id %d\n", buddy);
1203                 WARN_ON(1);
1204                 addr = NULL;
1205                 break;
1206         }
1207
1208         if (addr)
1209                 zhdr->mapped_count++;
1210 out:
1211         put_z3fold_header(zhdr);
1212         return addr;
1213 }
1214
1215 /**
1216  * z3fold_unmap() - unmaps the allocation associated with the given handle
1217  * @pool:       pool in which the allocation resides
1218  * @handle:     handle associated with the allocation to be unmapped
1219  */
1220 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
1221 {
1222         struct z3fold_header *zhdr;
1223         struct page *page;
1224         enum buddy buddy;
1225
1226         zhdr = get_z3fold_header(handle);
1227         page = virt_to_page(zhdr);
1228
1229         if (test_bit(PAGE_HEADLESS, &page->private))
1230                 return;
1231
1232         buddy = handle_to_buddy(handle);
1233         if (buddy == MIDDLE)
1234                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1235         zhdr->mapped_count--;
1236         put_z3fold_header(zhdr);
1237 }
1238
1239 /**
1240  * z3fold_get_pool_size() - gets the z3fold pool size in pages
1241  * @pool:       pool whose size is being queried
1242  *
1243  * Returns: size in pages of the given pool.
1244  */
1245 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
1246 {
1247         return atomic64_read(&pool->pages_nr);
1248 }
1249
1250 static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
1251 {
1252         struct z3fold_header *zhdr;
1253         struct z3fold_pool *pool;
1254
1255         VM_BUG_ON_PAGE(PageIsolated(page), page);
1256
1257         if (test_bit(PAGE_HEADLESS, &page->private))
1258                 return false;
1259
1260         zhdr = page_address(page);
1261         z3fold_page_lock(zhdr);
1262         if (test_bit(NEEDS_COMPACTING, &page->private) ||
1263             test_bit(PAGE_STALE, &page->private))
1264                 goto out;
1265
1266         if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0)
1267                 goto out;
1268
1269         if (test_and_set_bit(PAGE_CLAIMED, &page->private))
1270                 goto out;
1271         pool = zhdr_to_pool(zhdr);
1272         spin_lock(&pool->lock);
1273         if (!list_empty(&zhdr->buddy))
1274                 list_del_init(&zhdr->buddy);
1275         spin_unlock(&pool->lock);
1276
1277         kref_get(&zhdr->refcount);
1278         z3fold_page_unlock(zhdr);
1279         return true;
1280
1281 out:
1282         z3fold_page_unlock(zhdr);
1283         return false;
1284 }
1285
1286 static int z3fold_page_migrate(struct page *newpage, struct page *page,
1287                 enum migrate_mode mode)
1288 {
1289         struct z3fold_header *zhdr, *new_zhdr;
1290         struct z3fold_pool *pool;
1291
1292         VM_BUG_ON_PAGE(!PageIsolated(page), page);
1293         VM_BUG_ON_PAGE(!test_bit(PAGE_CLAIMED, &page->private), page);
1294         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1295
1296         zhdr = page_address(page);
1297         pool = zhdr_to_pool(zhdr);
1298
1299         if (!z3fold_page_trylock(zhdr))
1300                 return -EAGAIN;
1301         if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
1302                 clear_bit(PAGE_CLAIMED, &page->private);
1303                 z3fold_page_unlock(zhdr);
1304                 return -EBUSY;
1305         }
1306         if (work_pending(&zhdr->work)) {
1307                 z3fold_page_unlock(zhdr);
1308                 return -EAGAIN;
1309         }
1310         new_zhdr = page_address(newpage);
1311         memcpy(new_zhdr, zhdr, PAGE_SIZE);
1312         newpage->private = page->private;
1313         set_bit(PAGE_MIGRATED, &page->private);
1314         z3fold_page_unlock(zhdr);
1315         spin_lock_init(&new_zhdr->page_lock);
1316         INIT_WORK(&new_zhdr->work, compact_page_work);
1317         /*
1318          * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
1319          * so we only have to reinitialize it.
1320          */
1321         INIT_LIST_HEAD(&new_zhdr->buddy);
1322         __ClearPageMovable(page);
1323
1324         get_page(newpage);
1325         z3fold_page_lock(new_zhdr);
1326         if (new_zhdr->first_chunks)
1327                 encode_handle(new_zhdr, FIRST);
1328         if (new_zhdr->last_chunks)
1329                 encode_handle(new_zhdr, LAST);
1330         if (new_zhdr->middle_chunks)
1331                 encode_handle(new_zhdr, MIDDLE);
1332         set_bit(NEEDS_COMPACTING, &newpage->private);
1333         new_zhdr->cpu = smp_processor_id();
1334         __SetPageMovable(newpage, &z3fold_mops);
1335         z3fold_page_unlock(new_zhdr);
1336
1337         queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
1338
1339         /* PAGE_CLAIMED and PAGE_MIGRATED are cleared now. */
1340         page->private = 0;
1341         put_page(page);
1342         return 0;
1343 }
1344
1345 static void z3fold_page_putback(struct page *page)
1346 {
1347         struct z3fold_header *zhdr;
1348         struct z3fold_pool *pool;
1349
1350         zhdr = page_address(page);
1351         pool = zhdr_to_pool(zhdr);
1352
1353         z3fold_page_lock(zhdr);
1354         if (!list_empty(&zhdr->buddy))
1355                 list_del_init(&zhdr->buddy);
1356         INIT_LIST_HEAD(&page->lru);
1357         if (put_z3fold_locked(zhdr))
1358                 return;
1359         if (list_empty(&zhdr->buddy))
1360                 add_to_unbuddied(pool, zhdr);
1361         clear_bit(PAGE_CLAIMED, &page->private);
1362         z3fold_page_unlock(zhdr);
1363 }
1364
1365 static const struct movable_operations z3fold_mops = {
1366         .isolate_page = z3fold_page_isolate,
1367         .migrate_page = z3fold_page_migrate,
1368         .putback_page = z3fold_page_putback,
1369 };
1370
1371 /*****************
1372  * zpool
1373  ****************/
1374
1375 static void *z3fold_zpool_create(const char *name, gfp_t gfp)
1376 {
1377         return z3fold_create_pool(name, gfp);
1378 }
1379
1380 static void z3fold_zpool_destroy(void *pool)
1381 {
1382         z3fold_destroy_pool(pool);
1383 }
1384
1385 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1386                         unsigned long *handle)
1387 {
1388         return z3fold_alloc(pool, size, gfp, handle);
1389 }
1390 static void z3fold_zpool_free(void *pool, unsigned long handle)
1391 {
1392         z3fold_free(pool, handle);
1393 }
1394
1395 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1396                         enum zpool_mapmode mm)
1397 {
1398         return z3fold_map(pool, handle);
1399 }
1400 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1401 {
1402         z3fold_unmap(pool, handle);
1403 }
1404
1405 static u64 z3fold_zpool_total_size(void *pool)
1406 {
1407         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1408 }
1409
1410 static struct zpool_driver z3fold_zpool_driver = {
1411         .type =         "z3fold",
1412         .sleep_mapped = true,
1413         .owner =        THIS_MODULE,
1414         .create =       z3fold_zpool_create,
1415         .destroy =      z3fold_zpool_destroy,
1416         .malloc =       z3fold_zpool_malloc,
1417         .free =         z3fold_zpool_free,
1418         .map =          z3fold_zpool_map,
1419         .unmap =        z3fold_zpool_unmap,
1420         .total_size =   z3fold_zpool_total_size,
1421 };
1422
1423 MODULE_ALIAS("zpool-z3fold");
1424
1425 static int __init init_z3fold(void)
1426 {
1427         /*
1428          * Make sure the z3fold header is not larger than the page size and
1429          * there has remaining spaces for its buddy.
1430          */
1431         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
1432         zpool_register_driver(&z3fold_zpool_driver);
1433
1434         return 0;
1435 }
1436
1437 static void __exit exit_z3fold(void)
1438 {
1439         zpool_unregister_driver(&z3fold_zpool_driver);
1440 }
1441
1442 module_init(init_z3fold);
1443 module_exit(exit_z3fold);
1444
1445 MODULE_LICENSE("GPL");
1446 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1447 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");