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/mount.h>
  38 #include <linux/pseudo_fs.h>
  39 #include <linux/fs.h>
  40 #include <linux/preempt.h>
  41 #include <linux/workqueue.h>
  42 #include <linux/slab.h>
  43 #include <linux/spinlock.h>
  44 #include <linux/zpool.h>
  45 #include <linux/magic.h>
  46 #include <linux/kmemleak.h>
  47
  48 /*
  49  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
  50  * adjusting internal fragmentation.  It also determines the number of
  51  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
  52  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
  53  * in the beginning of an allocated page are occupied by z3fold header, so
  54  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
  55  * which shows the max number of free chunks in z3fold page, also there will
  56  * be 63, or 62, respectively, freelists per pool.
  57  */
  58 #define NCHUNKS_ORDER   6
  59
  60 #define CHUNK_SHIFT     (PAGE_SHIFT - NCHUNKS_ORDER)
  61 #define CHUNK_SIZE      (1 << CHUNK_SHIFT)
  62 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
  63 #define ZHDR_CHUNKS     (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
  64 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
  65 #define NCHUNKS         ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
  66
  67 #define BUDDY_MASK      (0x3)
  68 #define BUDDY_SHIFT     2
  69 #define SLOTS_ALIGN     (0x40)
  70
  71 /*****************
  72  * Structures
  73 *****************/
  74 struct z3fold_pool;
  75 struct z3fold_ops {
  76         int (*evict)(struct z3fold_pool *pool, unsigned long handle);
  77 };
  78
  79 enum buddy {
  80         HEADLESS = 0,
  81         FIRST,
  82         MIDDLE,
  83         LAST,
  84         BUDDIES_MAX = LAST
  85 };
  86
  87 struct z3fold_buddy_slots {
  88         /*
  89          * we are using BUDDY_MASK in handle_to_buddy etc. so there should
  90          * be enough slots to hold all possible variants
  91          */
  92         unsigned long slot[BUDDY_MASK + 1];
  93         unsigned long pool; /* back link + flags */
  94         rwlock_t lock;
  95 };
  96 #define HANDLE_FLAG_MASK        (0x03)
  97
  98 /*
  99  * struct z3fold_header - z3fold page metadata occupying first chunks of each
 100  *                      z3fold page, except for HEADLESS pages
 101  * @buddy:              links the z3fold page into the relevant list in the
 102  *                      pool
 103  * @page_lock:          per-page lock
 104  * @refcount:           reference count for the z3fold page
 105  * @work:               work_struct for page layout optimization
 106  * @slots:              pointer to the structure holding buddy slots
 107  * @pool:               pointer to the containing pool
 108  * @cpu:                CPU which this page "belongs" to
 109  * @first_chunks:       the size of the first buddy in chunks, 0 if free
 110  * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
 111  * @last_chunks:        the size of the last buddy in chunks, 0 if free
 112  * @first_num:          the starting number (for the first handle)
 113  * @mapped_count:       the number of objects currently mapped
 114  */
 115 struct z3fold_header {
 116         struct list_head buddy;
 117         spinlock_t page_lock;
 118         struct kref refcount;
 119         struct work_struct work;
 120         struct z3fold_buddy_slots *slots;
 121         struct z3fold_pool *pool;
 122         short cpu;
 123         unsigned short first_chunks;
 124         unsigned short middle_chunks;
 125         unsigned short last_chunks;
 126         unsigned short start_middle;
 127         unsigned short first_num:2;
 128         unsigned short mapped_count:2;
 129         unsigned short foreign_handles:2;
 130 };
 131
 132 /**
 133  * struct z3fold_pool - stores metadata for each z3fold pool
 134  * @name:       pool name
 135  * @lock:       protects pool unbuddied/lru lists
 136  * @stale_lock: protects pool stale page list
 137  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
 138  *              buddies; the list each z3fold page is added to depends on
 139  *              the size of its free region.
 140  * @lru:        list tracking the z3fold pages in LRU order by most recently
 141  *              added buddy.
 142  * @stale:      list of pages marked for freeing
 143  * @pages_nr:   number of z3fold pages in the pool.
 144  * @c_handle:   cache for z3fold_buddy_slots allocation
 145  * @ops:        pointer to a structure of user defined operations specified at
 146  *              pool creation time.
 147  * @compact_wq: workqueue for page layout background optimization
 148  * @release_wq: workqueue for safe page release
 149  * @work:       work_struct for safe page release
 150  * @inode:      inode for z3fold pseudo filesystem
 151  *
 152  * This structure is allocated at pool creation time and maintains metadata
 153  * pertaining to a particular z3fold pool.
 154  */
 155 struct z3fold_pool {
 156         const char *name;
 157         spinlock_t lock;
 158         spinlock_t stale_lock;
 159         struct list_head *unbuddied;
 160         struct list_head lru;
 161         struct list_head stale;
 162         atomic64_t pages_nr;
 163         struct kmem_cache *c_handle;
 164         const struct z3fold_ops *ops;
 165         struct zpool *zpool;
 166         const struct zpool_ops *zpool_ops;
 167         struct workqueue_struct *compact_wq;
 168         struct workqueue_struct *release_wq;
 169         struct work_struct work;
 170         struct inode *inode;
 171 };
 172
 173 /*
 174  * Internal z3fold page flags
 175  */
 176 enum z3fold_page_flags {
 177         PAGE_HEADLESS = 0,
 178         MIDDLE_CHUNK_MAPPED,
 179         NEEDS_COMPACTING,
 180         PAGE_STALE,
 181         PAGE_CLAIMED, /* by either reclaim or free */
 182 };
 183
 184 /*
 185  * handle flags, go under HANDLE_FLAG_MASK
 186  */
 187 enum z3fold_handle_flags {
 188         HANDLES_ORPHANED = 0,
 189 };
 190
 191 /*
 192  * Forward declarations
 193  */
 194 static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool);
 195 static void compact_page_work(struct work_struct *w);
 196
 197 /*****************
 198  * Helpers
 199 *****************/
 200
 201 /* Converts an allocation size in bytes to size in z3fold chunks */
 202 static int size_to_chunks(size_t size)
 203 {
 204         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 205 }
 206
 207 #define for_each_unbuddied_list(_iter, _begin) \
 208         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 209
 210 static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
 211                                                         gfp_t gfp)
 212 {
 213         struct z3fold_buddy_slots *slots;
 214
 215         slots = kmem_cache_alloc(pool->c_handle,
 216                                  (gfp & ~(__GFP_HIGHMEM | __GFP_MOVABLE)));
 217
 218         if (slots) {
 219                 /* It will be freed separately in free_handle(). */
 220                 kmemleak_not_leak(slots);
 221                 memset(slots->slot, 0, sizeof(slots->slot));
 222                 slots->pool = (unsigned long)pool;
 223                 rwlock_init(&slots->lock);
 224         }
 225
 226         return slots;
 227 }
 228
 229 static inline struct z3fold_pool *slots_to_pool(struct z3fold_buddy_slots *s)
 230 {
 231         return (struct z3fold_pool *)(s->pool & ~HANDLE_FLAG_MASK);
 232 }
 233
 234 static inline struct z3fold_buddy_slots *handle_to_slots(unsigned long handle)
 235 {
 236         return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
 237 }
 238
 239 /* Lock a z3fold page */
 240 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 241 {
 242         spin_lock(&zhdr->page_lock);
 243 }
 244
 245 /* Try to lock a z3fold page */
 246 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 247 {
 248         return spin_trylock(&zhdr->page_lock);
 249 }
 250
 251 /* Unlock a z3fold page */
 252 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 253 {
 254         spin_unlock(&zhdr->page_lock);
 255 }
 256
 257
 258 static inline struct z3fold_header *__get_z3fold_header(unsigned long handle,
 259                                                         bool lock)
 260 {
 261         struct z3fold_buddy_slots *slots;
 262         struct z3fold_header *zhdr;
 263         int locked = 0;
 264
 265         if (!(handle & (1 << PAGE_HEADLESS))) {
 266                 slots = handle_to_slots(handle);
 267                 do {
 268                         unsigned long addr;
 269
 270                         read_lock(&slots->lock);
 271                         addr = *(unsigned long *)handle;
 272                         zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 273                         if (lock)
 274                                 locked = z3fold_page_trylock(zhdr);
 275                         read_unlock(&slots->lock);
 276                         if (locked)
 277                                 break;
 278                         cpu_relax();
 279                 } while (lock);
 280         } else {
 281                 zhdr = (struct z3fold_header *)(handle & PAGE_MASK);
 282         }
 283
 284         return zhdr;
 285 }
 286
 287 /* Returns the z3fold page where a given handle is stored */
 288 static inline struct z3fold_header *handle_to_z3fold_header(unsigned long h)
 289 {
 290         return __get_z3fold_header(h, false);
 291 }
 292
 293 /* return locked z3fold page if it's not headless */
 294 static inline struct z3fold_header *get_z3fold_header(unsigned long h)
 295 {
 296         return __get_z3fold_header(h, true);
 297 }
 298
 299 static inline void put_z3fold_header(struct z3fold_header *zhdr)
 300 {
 301         struct page *page = virt_to_page(zhdr);
 302
 303         if (!test_bit(PAGE_HEADLESS, &page->private))
 304                 z3fold_page_unlock(zhdr);
 305 }
 306
 307 static inline void free_handle(unsigned long handle)
 308 {
 309         struct z3fold_buddy_slots *slots;
 310         struct z3fold_header *zhdr;
 311         int i;
 312         bool is_free;
 313
 314         if (handle & (1 << PAGE_HEADLESS))
 315                 return;
 316
 317         if (WARN_ON(*(unsigned long *)handle == 0))
 318                 return;
 319
 320         zhdr = handle_to_z3fold_header(handle);
 321         slots = handle_to_slots(handle);
 322         write_lock(&slots->lock);
 323         *(unsigned long *)handle = 0;
 324         if (zhdr->slots == slots) {
 325                 write_unlock(&slots->lock);
 326                 return; /* simple case, nothing else to do */
 327         }
 328
 329         /* we are freeing a foreign handle if we are here */
 330         zhdr->foreign_handles--;
 331         is_free = true;
 332         if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
 333                 write_unlock(&slots->lock);
 334                 return;
 335         }
 336         for (i = 0; i <= BUDDY_MASK; i++) {
 337                 if (slots->slot[i]) {
 338                         is_free = false;
 339                         break;
 340                 }
 341         }
 342         write_unlock(&slots->lock);
 343
 344         if (is_free) {
 345                 struct z3fold_pool *pool = slots_to_pool(slots);
 346
 347                 kmem_cache_free(pool->c_handle, slots);
 348         }
 349 }
 350
 351 static int z3fold_init_fs_context(struct fs_context *fc)
 352 {
 353         return init_pseudo(fc, Z3FOLD_MAGIC) ? 0 : -ENOMEM;
 354 }
 355
 356 static struct file_system_type z3fold_fs = {
 357         .name           = "z3fold",
 358         .init_fs_context = z3fold_init_fs_context,
 359         .kill_sb        = kill_anon_super,
 360 };
 361
 362 static struct vfsmount *z3fold_mnt;
 363 static int z3fold_mount(void)
 364 {
 365         int ret = 0;
 366
 367         z3fold_mnt = kern_mount(&z3fold_fs);
 368         if (IS_ERR(z3fold_mnt))
 369                 ret = PTR_ERR(z3fold_mnt);
 370
 371         return ret;
 372 }
 373
 374 static void z3fold_unmount(void)
 375 {
 376         kern_unmount(z3fold_mnt);
 377 }
 378
 379 static const struct address_space_operations z3fold_aops;
 380 static int z3fold_register_migration(struct z3fold_pool *pool)
 381 {
 382         pool->inode = alloc_anon_inode(z3fold_mnt->mnt_sb);
 383         if (IS_ERR(pool->inode)) {
 384                 pool->inode = NULL;
 385                 return 1;
 386         }
 387
 388         pool->inode->i_mapping->private_data = pool;
 389         pool->inode->i_mapping->a_ops = &z3fold_aops;
 390         return 0;
 391 }
 392
 393 static void z3fold_unregister_migration(struct z3fold_pool *pool)
 394 {
 395         if (pool->inode)
 396                 iput(pool->inode);
 397  }
 398
 399 /* Initializes the z3fold header of a newly allocated z3fold page */
 400 static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
 401                                         struct z3fold_pool *pool, gfp_t gfp)
 402 {
 403         struct z3fold_header *zhdr = page_address(page);
 404         struct z3fold_buddy_slots *slots;
 405
 406         INIT_LIST_HEAD(&page->lru);
 407         clear_bit(PAGE_HEADLESS, &page->private);
 408         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 409         clear_bit(NEEDS_COMPACTING, &page->private);
 410         clear_bit(PAGE_STALE, &page->private);
 411         clear_bit(PAGE_CLAIMED, &page->private);
 412         if (headless)
 413                 return zhdr;
 414
 415         slots = alloc_slots(pool, gfp);
 416         if (!slots)
 417                 return NULL;
 418
 419         spin_lock_init(&zhdr->page_lock);
 420         kref_init(&zhdr->refcount);
 421         zhdr->first_chunks = 0;
 422         zhdr->middle_chunks = 0;
 423         zhdr->last_chunks = 0;
 424         zhdr->first_num = 0;
 425         zhdr->start_middle = 0;
 426         zhdr->cpu = -1;
 427         zhdr->foreign_handles = 0;
 428         zhdr->mapped_count = 0;
 429         zhdr->slots = slots;
 430         zhdr->pool = pool;
 431         INIT_LIST_HEAD(&zhdr->buddy);
 432         INIT_WORK(&zhdr->work, compact_page_work);
 433         return zhdr;
 434 }
 435
 436 /* Resets the struct page fields and frees the page */
 437 static void free_z3fold_page(struct page *page, bool headless)
 438 {
 439         if (!headless) {
 440                 lock_page(page);
 441                 __ClearPageMovable(page);
 442                 unlock_page(page);
 443         }
 444         ClearPagePrivate(page);
 445         __free_page(page);
 446 }
 447
 448 /* Helper function to build the index */
 449 static inline int __idx(struct z3fold_header *zhdr, enum buddy bud)
 450 {
 451         return (bud + zhdr->first_num) & BUDDY_MASK;
 452 }
 453
 454 /*
 455  * Encodes the handle of a particular buddy within a z3fold page
 456  * Pool lock should be held as this function accesses first_num
 457  */
 458 static unsigned long __encode_handle(struct z3fold_header *zhdr,
 459                                 struct z3fold_buddy_slots *slots,
 460                                 enum buddy bud)
 461 {
 462         unsigned long h = (unsigned long)zhdr;
 463         int idx = 0;
 464
 465         /*
 466          * For a headless page, its handle is its pointer with the extra
 467          * PAGE_HEADLESS bit set
 468          */
 469         if (bud == HEADLESS)
 470                 return h | (1 << PAGE_HEADLESS);
 471
 472         /* otherwise, return pointer to encoded handle */
 473         idx = __idx(zhdr, bud);
 474         h += idx;
 475         if (bud == LAST)
 476                 h |= (zhdr->last_chunks << BUDDY_SHIFT);
 477
 478         write_lock(&slots->lock);
 479         slots->slot[idx] = h;
 480         write_unlock(&slots->lock);
 481         return (unsigned long)&slots->slot[idx];
 482 }
 483
 484 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 485 {
 486         return __encode_handle(zhdr, zhdr->slots, bud);
 487 }
 488
 489 /* only for LAST bud, returns zero otherwise */
 490 static unsigned short handle_to_chunks(unsigned long handle)
 491 {
 492         struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 493         unsigned long addr;
 494
 495         read_lock(&slots->lock);
 496         addr = *(unsigned long *)handle;
 497         read_unlock(&slots->lock);
 498         return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 499 }
 500
 501 /*
 502  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
 503  *  but that doesn't matter. because the masking will result in the
 504  *  correct buddy number.
 505  */
 506 static enum buddy handle_to_buddy(unsigned long handle)
 507 {
 508         struct z3fold_header *zhdr;
 509         struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 510         unsigned long addr;
 511
 512         read_lock(&slots->lock);
 513         WARN_ON(handle & (1 << PAGE_HEADLESS));
 514         addr = *(unsigned long *)handle;
 515         read_unlock(&slots->lock);
 516         zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 517         return (addr - zhdr->first_num) & BUDDY_MASK;
 518 }
 519
 520 static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
 521 {
 522         return zhdr->pool;
 523 }
 524
 525 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 526 {
 527         struct page *page = virt_to_page(zhdr);
 528         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 529         bool is_free = true;
 530         int i;
 531
 532         WARN_ON(!list_empty(&zhdr->buddy));
 533         set_bit(PAGE_STALE, &page->private);
 534         clear_bit(NEEDS_COMPACTING, &page->private);
 535         spin_lock(&pool->lock);
 536         if (!list_empty(&page->lru))
 537                 list_del_init(&page->lru);
 538         spin_unlock(&pool->lock);
 539
 540         /* If there are no foreign handles, free the handles array */
 541         read_lock(&zhdr->slots->lock);
 542         for (i = 0; i <= BUDDY_MASK; i++) {
 543                 if (zhdr->slots->slot[i]) {
 544                         is_free = false;
 545                         break;
 546                 }
 547         }
 548         if (!is_free)
 549                 set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
 550         read_unlock(&zhdr->slots->lock);
 551
 552         if (is_free)
 553                 kmem_cache_free(pool->c_handle, zhdr->slots);
 554
 555         if (locked)
 556                 z3fold_page_unlock(zhdr);
 557
 558         spin_lock(&pool->stale_lock);
 559         list_add(&zhdr->buddy, &pool->stale);
 560         queue_work(pool->release_wq, &pool->work);
 561         spin_unlock(&pool->stale_lock);
 562 }
 563
 564 static void __attribute__((__unused__))
 565                         release_z3fold_page(struct kref *ref)
 566 {
 567         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 568                                                 refcount);
 569         __release_z3fold_page(zhdr, false);
 570 }
 571
 572 static void release_z3fold_page_locked(struct kref *ref)
 573 {
 574         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 575                                                 refcount);
 576         WARN_ON(z3fold_page_trylock(zhdr));
 577         __release_z3fold_page(zhdr, true);
 578 }
 579
 580 static void release_z3fold_page_locked_list(struct kref *ref)
 581 {
 582         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 583                                                refcount);
 584         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 585
 586         spin_lock(&pool->lock);
 587         list_del_init(&zhdr->buddy);
 588         spin_unlock(&pool->lock);
 589
 590         WARN_ON(z3fold_page_trylock(zhdr));
 591         __release_z3fold_page(zhdr, true);
 592 }
 593
 594 static void free_pages_work(struct work_struct *w)
 595 {
 596         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 597
 598         spin_lock(&pool->stale_lock);
 599         while (!list_empty(&pool->stale)) {
 600                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
 601                                                 struct z3fold_header, buddy);
 602                 struct page *page = virt_to_page(zhdr);
 603
 604                 list_del(&zhdr->buddy);
 605                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
 606                         continue;
 607                 spin_unlock(&pool->stale_lock);
 608                 cancel_work_sync(&zhdr->work);
 609                 free_z3fold_page(page, false);
 610                 cond_resched();
 611                 spin_lock(&pool->stale_lock);
 612         }
 613         spin_unlock(&pool->stale_lock);
 614 }
 615
 616 /*
 617  * Returns the number of free chunks in a z3fold page.
 618  * NB: can't be used with HEADLESS pages.
 619  */
 620 static int num_free_chunks(struct z3fold_header *zhdr)
 621 {
 622         int nfree;
 623         /*
 624          * If there is a middle object, pick up the bigger free space
 625          * either before or after it. Otherwise just subtract the number
 626          * of chunks occupied by the first and the last objects.
 627          */
 628         if (zhdr->middle_chunks != 0) {
 629                 int nfree_before = zhdr->first_chunks ?
 630                         0 : zhdr->start_middle - ZHDR_CHUNKS;
 631                 int nfree_after = zhdr->last_chunks ?
 632                         0 : TOTAL_CHUNKS -
 633                                 (zhdr->start_middle + zhdr->middle_chunks);
 634                 nfree = max(nfree_before, nfree_after);
 635         } else
 636                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
 637         return nfree;
 638 }
 639
 640 /* Add to the appropriate unbuddied list */
 641 static inline void add_to_unbuddied(struct z3fold_pool *pool,
 642                                 struct z3fold_header *zhdr)
 643 {
 644         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 645                         zhdr->middle_chunks == 0) {
 646                 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
 647
 648                 int freechunks = num_free_chunks(zhdr);
 649                 spin_lock(&pool->lock);
 650                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
 651                 spin_unlock(&pool->lock);
 652                 zhdr->cpu = smp_processor_id();
 653                 put_cpu_ptr(pool->unbuddied);
 654         }
 655 }
 656
 657 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 658                                 unsigned short dst_chunk)
 659 {
 660         void *beg = zhdr;
 661         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
 662                        beg + (zhdr->start_middle << CHUNK_SHIFT),
 663                        zhdr->middle_chunks << CHUNK_SHIFT);
 664 }
 665
 666 static inline bool buddy_single(struct z3fold_header *zhdr)
 667 {
 668         return !((zhdr->first_chunks && zhdr->middle_chunks) ||
 669                         (zhdr->first_chunks && zhdr->last_chunks) ||
 670                         (zhdr->middle_chunks && zhdr->last_chunks));
 671 }
 672
 673 static struct z3fold_header *compact_single_buddy(struct z3fold_header *zhdr)
 674 {
 675         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 676         void *p = zhdr;
 677         unsigned long old_handle = 0;
 678         size_t sz = 0;
 679         struct z3fold_header *new_zhdr = NULL;
 680         int first_idx = __idx(zhdr, FIRST);
 681         int middle_idx = __idx(zhdr, MIDDLE);
 682         int last_idx = __idx(zhdr, LAST);
 683         unsigned short *moved_chunks = NULL;
 684
 685         /*
 686          * No need to protect slots here -- all the slots are "local" and
 687          * the page lock is already taken
 688          */
 689         if (zhdr->first_chunks && zhdr->slots->slot[first_idx]) {
 690                 p += ZHDR_SIZE_ALIGNED;
 691                 sz = zhdr->first_chunks << CHUNK_SHIFT;
 692                 old_handle = (unsigned long)&zhdr->slots->slot[first_idx];
 693                 moved_chunks = &zhdr->first_chunks;
 694         } else if (zhdr->middle_chunks && zhdr->slots->slot[middle_idx]) {
 695                 p += zhdr->start_middle << CHUNK_SHIFT;
 696                 sz = zhdr->middle_chunks << CHUNK_SHIFT;
 697                 old_handle = (unsigned long)&zhdr->slots->slot[middle_idx];
 698                 moved_chunks = &zhdr->middle_chunks;
 699         } else if (zhdr->last_chunks && zhdr->slots->slot[last_idx]) {
 700                 p += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
 701                 sz = zhdr->last_chunks << CHUNK_SHIFT;
 702                 old_handle = (unsigned long)&zhdr->slots->slot[last_idx];
 703                 moved_chunks = &zhdr->last_chunks;
 704         }
 705
 706         if (sz > 0) {
 707                 enum buddy new_bud = HEADLESS;
 708                 short chunks = size_to_chunks(sz);
 709                 void *q;
 710
 711                 new_zhdr = __z3fold_alloc(pool, sz, false);
 712                 if (!new_zhdr)
 713                         return NULL;
 714
 715                 if (WARN_ON(new_zhdr == zhdr))
 716                         goto out_fail;
 717
 718                 if (new_zhdr->first_chunks == 0) {
 719                         if (new_zhdr->middle_chunks != 0 &&
 720                                         chunks >= new_zhdr->start_middle) {
 721                                 new_bud = LAST;
 722                         } else {
 723                                 new_bud = FIRST;
 724                         }
 725                 } else if (new_zhdr->last_chunks == 0) {
 726                         new_bud = LAST;
 727                 } else if (new_zhdr->middle_chunks == 0) {
 728                         new_bud = MIDDLE;
 729                 }
 730                 q = new_zhdr;
 731                 switch (new_bud) {
 732                 case FIRST:
 733                         new_zhdr->first_chunks = chunks;
 734                         q += ZHDR_SIZE_ALIGNED;
 735                         break;
 736                 case MIDDLE:
 737                         new_zhdr->middle_chunks = chunks;
 738                         new_zhdr->start_middle =
 739                                 new_zhdr->first_chunks + ZHDR_CHUNKS;
 740                         q += new_zhdr->start_middle << CHUNK_SHIFT;
 741                         break;
 742                 case LAST:
 743                         new_zhdr->last_chunks = chunks;
 744                         q += PAGE_SIZE - (new_zhdr->last_chunks << CHUNK_SHIFT);
 745                         break;
 746                 default:
 747                         goto out_fail;
 748                 }
 749                 new_zhdr->foreign_handles++;
 750                 memcpy(q, p, sz);
 751                 write_lock(&zhdr->slots->lock);
 752                 *(unsigned long *)old_handle = (unsigned long)new_zhdr +
 753                         __idx(new_zhdr, new_bud);
 754                 if (new_bud == LAST)
 755                         *(unsigned long *)old_handle |=
 756                                         (new_zhdr->last_chunks << BUDDY_SHIFT);
 757                 write_unlock(&zhdr->slots->lock);
 758                 add_to_unbuddied(pool, new_zhdr);
 759                 z3fold_page_unlock(new_zhdr);
 760
 761                 *moved_chunks = 0;
 762         }
 763
 764         return new_zhdr;
 765
 766 out_fail:
 767         if (new_zhdr) {
 768                 if (kref_put(&new_zhdr->refcount, release_z3fold_page_locked))
 769                         atomic64_dec(&pool->pages_nr);
 770                 else {
 771                         add_to_unbuddied(pool, new_zhdr);
 772                         z3fold_page_unlock(new_zhdr);
 773                 }
 774         }
 775         return NULL;
 776
 777 }
 778
 779 #define BIG_CHUNK_GAP   3
 780 /* Has to be called with lock held */
 781 static int z3fold_compact_page(struct z3fold_header *zhdr)
 782 {
 783         struct page *page = virt_to_page(zhdr);
 784
 785         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 786                 return 0; /* can't move middle chunk, it's used */
 787
 788         if (unlikely(PageIsolated(page)))
 789                 return 0;
 790
 791         if (zhdr->middle_chunks == 0)
 792                 return 0; /* nothing to compact */
 793
 794         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
 795                 /* move to the beginning */
 796                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
 797                 zhdr->first_chunks = zhdr->middle_chunks;
 798                 zhdr->middle_chunks = 0;
 799                 zhdr->start_middle = 0;
 800                 zhdr->first_num++;
 801                 return 1;
 802         }
 803
 804         /*
 805          * moving data is expensive, so let's only do that if
 806          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
 807          */
 808         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
 809             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
 810                         BIG_CHUNK_GAP) {
 811                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
 812                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 813                 return 1;
 814         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
 815                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
 816                                         + zhdr->middle_chunks) >=
 817                         BIG_CHUNK_GAP) {
 818                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
 819                         zhdr->middle_chunks;
 820                 mchunk_memmove(zhdr, new_start);
 821                 zhdr->start_middle = new_start;
 822                 return 1;
 823         }
 824
 825         return 0;
 826 }
 827
 828 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 829 {
 830         struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 831         struct page *page;
 832
 833         page = virt_to_page(zhdr);
 834         if (locked)
 835                 WARN_ON(z3fold_page_trylock(zhdr));
 836         else
 837                 z3fold_page_lock(zhdr);
 838         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
 839                 z3fold_page_unlock(zhdr);
 840                 return;
 841         }
 842         spin_lock(&pool->lock);
 843         list_del_init(&zhdr->buddy);
 844         spin_unlock(&pool->lock);
 845
 846         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
 847                 atomic64_dec(&pool->pages_nr);
 848                 return;
 849         }
 850
 851         if (unlikely(PageIsolated(page) ||
 852                      test_bit(PAGE_CLAIMED, &page->private) ||
 853                      test_bit(PAGE_STALE, &page->private))) {
 854                 z3fold_page_unlock(zhdr);
 855                 return;
 856         }
 857
 858         if (!zhdr->foreign_handles && buddy_single(zhdr) &&
 859             zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) {
 860                 if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
 861                         atomic64_dec(&pool->pages_nr);
 862                 else
 863                         z3fold_page_unlock(zhdr);
 864                 return;
 865         }
 866
 867         z3fold_compact_page(zhdr);
 868         add_to_unbuddied(pool, zhdr);
 869         z3fold_page_unlock(zhdr);
 870 }
 871
 872 static void compact_page_work(struct work_struct *w)
 873 {
 874         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
 875                                                 work);
 876
 877         do_compact_page(zhdr, false);
 878 }
 879
 880 /* returns _locked_ z3fold page header or NULL */
 881 static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
 882                                                 size_t size, bool can_sleep)
 883 {
 884         struct z3fold_header *zhdr = NULL;
 885         struct page *page;
 886         struct list_head *unbuddied;
 887         int chunks = size_to_chunks(size), i;
 888
 889 lookup:
 890         /* First, try to find an unbuddied z3fold page. */
 891         unbuddied = get_cpu_ptr(pool->unbuddied);
 892         for_each_unbuddied_list(i, chunks) {
 893                 struct list_head *l = &unbuddied[i];
 894
 895                 zhdr = list_first_entry_or_null(READ_ONCE(l),
 896                                         struct z3fold_header, buddy);
 897
 898                 if (!zhdr)
 899                         continue;
 900
 901                 /* Re-check under lock. */
 902                 spin_lock(&pool->lock);
 903                 l = &unbuddied[i];
 904                 if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
 905                                                 struct z3fold_header, buddy)) ||
 906                     !z3fold_page_trylock(zhdr)) {
 907                         spin_unlock(&pool->lock);
 908                         zhdr = NULL;
 909                         put_cpu_ptr(pool->unbuddied);
 910                         if (can_sleep)
 911                                 cond_resched();
 912                         goto lookup;
 913                 }
 914                 list_del_init(&zhdr->buddy);
 915                 zhdr->cpu = -1;
 916                 spin_unlock(&pool->lock);
 917
 918                 page = virt_to_page(zhdr);
 919                 if (test_bit(NEEDS_COMPACTING, &page->private) ||
 920                     test_bit(PAGE_CLAIMED, &page->private)) {
 921                         z3fold_page_unlock(zhdr);
 922                         zhdr = NULL;
 923                         put_cpu_ptr(pool->unbuddied);
 924                         if (can_sleep)
 925                                 cond_resched();
 926                         goto lookup;
 927                 }
 928
 929                 /*
 930                  * this page could not be removed from its unbuddied
 931                  * list while pool lock was held, and then we've taken
 932                  * page lock so kref_put could not be called before
 933                  * we got here, so it's safe to just call kref_get()
 934                  */
 935                 kref_get(&zhdr->refcount);
 936                 break;
 937         }
 938         put_cpu_ptr(pool->unbuddied);
 939
 940         if (!zhdr) {
 941                 int cpu;
 942
 943                 /* look for _exact_ match on other cpus' lists */
 944                 for_each_online_cpu(cpu) {
 945                         struct list_head *l;
 946
 947                         unbuddied = per_cpu_ptr(pool->unbuddied, cpu);
 948                         spin_lock(&pool->lock);
 949                         l = &unbuddied[chunks];
 950
 951                         zhdr = list_first_entry_or_null(READ_ONCE(l),
 952                                                 struct z3fold_header, buddy);
 953
 954                         if (!zhdr || !z3fold_page_trylock(zhdr)) {
 955                                 spin_unlock(&pool->lock);
 956                                 zhdr = NULL;
 957                                 continue;
 958                         }
 959                         list_del_init(&zhdr->buddy);
 960                         zhdr->cpu = -1;
 961                         spin_unlock(&pool->lock);
 962
 963                         page = virt_to_page(zhdr);
 964                         if (test_bit(NEEDS_COMPACTING, &page->private) ||
 965                             test_bit(PAGE_CLAIMED, &page->private)) {
 966                                 z3fold_page_unlock(zhdr);
 967                                 zhdr = NULL;
 968                                 if (can_sleep)
 969                                         cond_resched();
 970                                 continue;
 971                         }
 972                         kref_get(&zhdr->refcount);
 973                         break;
 974                 }
 975         }
 976
 977         return zhdr;
 978 }
 979
 980 /*
 981  * API Functions
 982  */
 983
 984 /**
 985  * z3fold_create_pool() - create a new z3fold pool
 986  * @name:       pool name
 987  * @gfp:        gfp flags when allocating the z3fold pool structure
 988  * @ops:        user-defined operations for the z3fold pool
 989  *
 990  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
 991  * failed.
 992  */
 993 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
 994                 const struct z3fold_ops *ops)
 995 {
 996         struct z3fold_pool *pool = NULL;
 997         int i, cpu;
 998
 999         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
1000         if (!pool)
1001                 goto out;
1002         pool->c_handle = kmem_cache_create("z3fold_handle",
1003                                 sizeof(struct z3fold_buddy_slots),
1004                                 SLOTS_ALIGN, 0, NULL);
1005         if (!pool->c_handle)
1006                 goto out_c;
1007         spin_lock_init(&pool->lock);
1008         spin_lock_init(&pool->stale_lock);
1009         pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
1010         if (!pool->unbuddied)
1011                 goto out_pool;
1012         for_each_possible_cpu(cpu) {
1013                 struct list_head *unbuddied =
1014                                 per_cpu_ptr(pool->unbuddied, cpu);
1015                 for_each_unbuddied_list(i, 0)
1016                         INIT_LIST_HEAD(&unbuddied[i]);
1017         }
1018         INIT_LIST_HEAD(&pool->lru);
1019         INIT_LIST_HEAD(&pool->stale);
1020         atomic64_set(&pool->pages_nr, 0);
1021         pool->name = name;
1022         pool->compact_wq = create_singlethread_workqueue(pool->name);
1023         if (!pool->compact_wq)
1024                 goto out_unbuddied;
1025         pool->release_wq = create_singlethread_workqueue(pool->name);
1026         if (!pool->release_wq)
1027                 goto out_wq;
1028         if (z3fold_register_migration(pool))
1029                 goto out_rwq;
1030         INIT_WORK(&pool->work, free_pages_work);
1031         pool->ops = ops;
1032         return pool;
1033
1034 out_rwq:
1035         destroy_workqueue(pool->release_wq);
1036 out_wq:
1037         destroy_workqueue(pool->compact_wq);
1038 out_unbuddied:
1039         free_percpu(pool->unbuddied);
1040 out_pool:
1041         kmem_cache_destroy(pool->c_handle);
1042 out_c:
1043         kfree(pool);
1044 out:
1045         return NULL;
1046 }
1047
1048 /**
1049  * z3fold_destroy_pool() - destroys an existing z3fold pool
1050  * @pool:       the z3fold pool to be destroyed
1051  *
1052  * The pool should be emptied before this function is called.
1053  */
1054 static void z3fold_destroy_pool(struct z3fold_pool *pool)
1055 {
1056         kmem_cache_destroy(pool->c_handle);
1057
1058         /*
1059          * We need to destroy pool->compact_wq before pool->release_wq,
1060          * as any pending work on pool->compact_wq will call
1061          * queue_work(pool->release_wq, &pool->work).
1062          *
1063          * There are still outstanding pages until both workqueues are drained,
1064          * so we cannot unregister migration until then.
1065          */
1066
1067         destroy_workqueue(pool->compact_wq);
1068         destroy_workqueue(pool->release_wq);
1069         z3fold_unregister_migration(pool);
1070         kfree(pool);
1071 }
1072
1073 /**
1074  * z3fold_alloc() - allocates a region of a given size
1075  * @pool:       z3fold pool from which to allocate
1076  * @size:       size in bytes of the desired allocation
1077  * @gfp:        gfp flags used if the pool needs to grow
1078  * @handle:     handle of the new allocation
1079  *
1080  * This function will attempt to find a free region in the pool large enough to
1081  * satisfy the allocation request.  A search of the unbuddied lists is
1082  * performed first. If no suitable free region is found, then a new page is
1083  * allocated and added to the pool to satisfy the request.
1084  *
1085  * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
1086  * as z3fold pool pages.
1087  *
1088  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
1089  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
1090  * a new page.
1091  */
1092 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
1093                         unsigned long *handle)
1094 {
1095         int chunks = size_to_chunks(size);
1096         struct z3fold_header *zhdr = NULL;
1097         struct page *page = NULL;
1098         enum buddy bud;
1099         bool can_sleep = gfpflags_allow_blocking(gfp);
1100
1101         if (!size)
1102                 return -EINVAL;
1103
1104         if (size > PAGE_SIZE)
1105                 return -ENOSPC;
1106
1107         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
1108                 bud = HEADLESS;
1109         else {
1110 retry:
1111                 zhdr = __z3fold_alloc(pool, size, can_sleep);
1112                 if (zhdr) {
1113                         if (zhdr->first_chunks == 0) {
1114                                 if (zhdr->middle_chunks != 0 &&
1115                                     chunks >= zhdr->start_middle)
1116                                         bud = LAST;
1117                                 else
1118                                         bud = FIRST;
1119                         } else if (zhdr->last_chunks == 0)
1120                                 bud = LAST;
1121                         else if (zhdr->middle_chunks == 0)
1122                                 bud = MIDDLE;
1123                         else {
1124                                 if (kref_put(&zhdr->refcount,
1125                                              release_z3fold_page_locked))
1126                                         atomic64_dec(&pool->pages_nr);
1127                                 else
1128                                         z3fold_page_unlock(zhdr);
1129                                 pr_err("No free chunks in unbuddied\n");
1130                                 WARN_ON(1);
1131                                 goto retry;
1132                         }
1133                         page = virt_to_page(zhdr);
1134                         goto found;
1135                 }
1136                 bud = FIRST;
1137         }
1138
1139         page = NULL;
1140         if (can_sleep) {
1141                 spin_lock(&pool->stale_lock);
1142                 zhdr = list_first_entry_or_null(&pool->stale,
1143                                                 struct z3fold_header, buddy);
1144                 /*
1145                  * Before allocating a page, let's see if we can take one from
1146                  * the stale pages list. cancel_work_sync() can sleep so we
1147                  * limit this case to the contexts where we can sleep
1148                  */
1149                 if (zhdr) {
1150                         list_del(&zhdr->buddy);
1151                         spin_unlock(&pool->stale_lock);
1152                         cancel_work_sync(&zhdr->work);
1153                         page = virt_to_page(zhdr);
1154                 } else {
1155                         spin_unlock(&pool->stale_lock);
1156                 }
1157         }
1158         if (!page)
1159                 page = alloc_page(gfp);
1160
1161         if (!page)
1162                 return -ENOMEM;
1163
1164         zhdr = init_z3fold_page(page, bud == HEADLESS, pool, gfp);
1165         if (!zhdr) {
1166                 __free_page(page);
1167                 return -ENOMEM;
1168         }
1169         atomic64_inc(&pool->pages_nr);
1170
1171         if (bud == HEADLESS) {
1172                 set_bit(PAGE_HEADLESS, &page->private);
1173                 goto headless;
1174         }
1175         if (can_sleep) {
1176                 lock_page(page);
1177                 __SetPageMovable(page, pool->inode->i_mapping);
1178                 unlock_page(page);
1179         } else {
1180                 if (trylock_page(page)) {
1181                         __SetPageMovable(page, pool->inode->i_mapping);
1182                         unlock_page(page);
1183                 }
1184         }
1185         z3fold_page_lock(zhdr);
1186
1187 found:
1188         if (bud == FIRST)
1189                 zhdr->first_chunks = chunks;
1190         else if (bud == LAST)
1191                 zhdr->last_chunks = chunks;
1192         else {
1193                 zhdr->middle_chunks = chunks;
1194                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
1195         }
1196         add_to_unbuddied(pool, zhdr);
1197
1198 headless:
1199         spin_lock(&pool->lock);
1200         /* Add/move z3fold page to beginning of LRU */
1201         if (!list_empty(&page->lru))
1202                 list_del(&page->lru);
1203
1204         list_add(&page->lru, &pool->lru);
1205
1206         *handle = encode_handle(zhdr, bud);
1207         spin_unlock(&pool->lock);
1208         if (bud != HEADLESS)
1209                 z3fold_page_unlock(zhdr);
1210
1211         return 0;
1212 }
1213
1214 /**
1215  * z3fold_free() - frees the allocation associated with the given handle
1216  * @pool:       pool in which the allocation resided
1217  * @handle:     handle associated with the allocation returned by z3fold_alloc()
1218  *
1219  * In the case that the z3fold page in which the allocation resides is under
1220  * reclaim, as indicated by the PG_reclaim flag being set, this function
1221  * only sets the first|last_chunks to 0.  The page is actually freed
1222  * once both buddies are evicted (see z3fold_reclaim_page() below).
1223  */
1224 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
1225 {
1226         struct z3fold_header *zhdr;
1227         struct page *page;
1228         enum buddy bud;
1229         bool page_claimed;
1230
1231         zhdr = get_z3fold_header(handle);
1232         page = virt_to_page(zhdr);
1233         page_claimed = test_and_set_bit(PAGE_CLAIMED, &page->private);
1234
1235         if (test_bit(PAGE_HEADLESS, &page->private)) {
1236                 /* if a headless page is under reclaim, just leave.
1237                  * NB: we use test_and_set_bit for a reason: if the bit
1238                  * has not been set before, we release this page
1239                  * immediately so we don't care about its value any more.
1240                  */
1241                 if (!page_claimed) {
1242                         spin_lock(&pool->lock);
1243                         list_del(&page->lru);
1244                         spin_unlock(&pool->lock);
1245                         put_z3fold_header(zhdr);
1246                         free_z3fold_page(page, true);
1247                         atomic64_dec(&pool->pages_nr);
1248                 }
1249                 return;
1250         }
1251
1252         /* Non-headless case */
1253         bud = handle_to_buddy(handle);
1254
1255         switch (bud) {
1256         case FIRST:
1257                 zhdr->first_chunks = 0;
1258                 break;
1259         case MIDDLE:
1260                 zhdr->middle_chunks = 0;
1261                 break;
1262         case LAST:
1263                 zhdr->last_chunks = 0;
1264                 break;
1265         default:
1266                 pr_err("%s: unknown bud %d\n", __func__, bud);
1267                 WARN_ON(1);
1268                 put_z3fold_header(zhdr);
1269                 clear_bit(PAGE_CLAIMED, &page->private);
1270                 return;
1271         }
1272
1273         if (!page_claimed)
1274                 free_handle(handle);
1275         if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
1276                 atomic64_dec(&pool->pages_nr);
1277                 return;
1278         }
1279         if (page_claimed) {
1280                 /* the page has not been claimed by us */
1281                 z3fold_page_unlock(zhdr);
1282                 return;
1283         }
1284         if (unlikely(PageIsolated(page)) ||
1285             test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
1286                 put_z3fold_header(zhdr);
1287                 clear_bit(PAGE_CLAIMED, &page->private);
1288                 return;
1289         }
1290         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
1291                 spin_lock(&pool->lock);
1292                 list_del_init(&zhdr->buddy);
1293                 spin_unlock(&pool->lock);
1294                 zhdr->cpu = -1;
1295                 kref_get(&zhdr->refcount);
1296                 clear_bit(PAGE_CLAIMED, &page->private);
1297                 do_compact_page(zhdr, true);
1298                 return;
1299         }
1300         kref_get(&zhdr->refcount);
1301         clear_bit(PAGE_CLAIMED, &page->private);
1302         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
1303         put_z3fold_header(zhdr);
1304 }
1305
1306 /**
1307  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
1308  * @pool:       pool from which a page will attempt to be evicted
1309  * @retries:    number of pages on the LRU list for which eviction will
1310  *              be attempted before failing
1311  *
1312  * z3fold reclaim is different from normal system reclaim in that it is done
1313  * from the bottom, up. This is because only the bottom layer, z3fold, has
1314  * information on how the allocations are organized within each z3fold page.
1315  * This has the potential to create interesting locking situations between
1316  * z3fold and the user, however.
1317  *
1318  * To avoid these, this is how z3fold_reclaim_page() should be called:
1319  *
1320  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
1321  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
1322  * call the user-defined eviction handler with the pool and handle as
1323  * arguments.
1324  *
1325  * If the handle can not be evicted, the eviction handler should return
1326  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
1327  * appropriate list and try the next z3fold page on the LRU up to
1328  * a user defined number of retries.
1329  *
1330  * If the handle is successfully evicted, the eviction handler should
1331  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
1332  * contains logic to delay freeing the page if the page is under reclaim,
1333  * as indicated by the setting of the PG_reclaim flag on the underlying page.
1334  *
1335  * If all buddies in the z3fold page are successfully evicted, then the
1336  * z3fold page can be freed.
1337  *
1338  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
1339  * no pages to evict or an eviction handler is not registered, -EAGAIN if
1340  * the retry limit was hit.
1341  */
1342 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
1343 {
1344         int i, ret = -1;
1345         struct z3fold_header *zhdr = NULL;
1346         struct page *page = NULL;
1347         struct list_head *pos;
1348         unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
1349
1350         spin_lock(&pool->lock);
1351         if (!pool->ops || !pool->ops->evict || retries == 0) {
1352                 spin_unlock(&pool->lock);
1353                 return -EINVAL;
1354         }
1355         for (i = 0; i < retries; i++) {
1356                 if (list_empty(&pool->lru)) {
1357                         spin_unlock(&pool->lock);
1358                         return -EINVAL;
1359                 }
1360                 list_for_each_prev(pos, &pool->lru) {
1361                         page = list_entry(pos, struct page, lru);
1362
1363                         /* this bit could have been set by free, in which case
1364                          * we pass over to the next page in the pool.
1365                          */
1366                         if (test_and_set_bit(PAGE_CLAIMED, &page->private)) {
1367                                 page = NULL;
1368                                 continue;
1369                         }
1370
1371                         if (unlikely(PageIsolated(page))) {
1372                                 clear_bit(PAGE_CLAIMED, &page->private);
1373                                 page = NULL;
1374                                 continue;
1375                         }
1376                         zhdr = page_address(page);
1377                         if (test_bit(PAGE_HEADLESS, &page->private))
1378                                 break;
1379
1380                         if (!z3fold_page_trylock(zhdr)) {
1381                                 clear_bit(PAGE_CLAIMED, &page->private);
1382                                 zhdr = NULL;
1383                                 continue; /* can't evict at this point */
1384                         }
1385                         if (zhdr->foreign_handles) {
1386                                 clear_bit(PAGE_CLAIMED, &page->private);
1387                                 z3fold_page_unlock(zhdr);
1388                                 zhdr = NULL;
1389                                 continue; /* can't evict such page */
1390                         }
1391                         kref_get(&zhdr->refcount);
1392                         list_del_init(&zhdr->buddy);
1393                         zhdr->cpu = -1;
1394                         break;
1395                 }
1396
1397                 if (!zhdr)
1398                         break;
1399
1400                 list_del_init(&page->lru);
1401                 spin_unlock(&pool->lock);
1402
1403                 if (!test_bit(PAGE_HEADLESS, &page->private)) {
1404                         /*
1405                          * We need encode the handles before unlocking, and
1406                          * use our local slots structure because z3fold_free
1407                          * can zero out zhdr->slots and we can't do much
1408                          * about that
1409                          */
1410                         first_handle = 0;
1411                         last_handle = 0;
1412                         middle_handle = 0;
1413                         if (zhdr->first_chunks)
1414                                 first_handle = encode_handle(zhdr, FIRST);
1415                         if (zhdr->middle_chunks)
1416                                 middle_handle = encode_handle(zhdr, MIDDLE);
1417                         if (zhdr->last_chunks)
1418                                 last_handle = encode_handle(zhdr, LAST);
1419                         /*
1420                          * it's safe to unlock here because we hold a
1421                          * reference to this page
1422                          */
1423                         z3fold_page_unlock(zhdr);
1424                 } else {
1425                         first_handle = encode_handle(zhdr, HEADLESS);
1426                         last_handle = middle_handle = 0;
1427                 }
1428                 /* Issue the eviction callback(s) */
1429                 if (middle_handle) {
1430                         ret = pool->ops->evict(pool, middle_handle);
1431                         if (ret)
1432                                 goto next;
1433                         free_handle(middle_handle);
1434                 }
1435                 if (first_handle) {
1436                         ret = pool->ops->evict(pool, first_handle);
1437                         if (ret)
1438                                 goto next;
1439                         free_handle(first_handle);
1440                 }
1441                 if (last_handle) {
1442                         ret = pool->ops->evict(pool, last_handle);
1443                         if (ret)
1444                                 goto next;
1445                         free_handle(last_handle);
1446                 }
1447 next:
1448                 if (test_bit(PAGE_HEADLESS, &page->private)) {
1449                         if (ret == 0) {
1450                                 free_z3fold_page(page, true);
1451                                 atomic64_dec(&pool->pages_nr);
1452                                 return 0;
1453                         }
1454                         spin_lock(&pool->lock);
1455                         list_add(&page->lru, &pool->lru);
1456                         spin_unlock(&pool->lock);
1457                         clear_bit(PAGE_CLAIMED, &page->private);
1458                 } else {
1459                         z3fold_page_lock(zhdr);
1460                         if (kref_put(&zhdr->refcount,
1461                                         release_z3fold_page_locked)) {
1462                                 atomic64_dec(&pool->pages_nr);
1463                                 return 0;
1464                         }
1465                         /*
1466                          * if we are here, the page is still not completely
1467                          * free. Take the global pool lock then to be able
1468                          * to add it back to the lru list
1469                          */
1470                         spin_lock(&pool->lock);
1471                         list_add(&page->lru, &pool->lru);
1472                         spin_unlock(&pool->lock);
1473                         z3fold_page_unlock(zhdr);
1474                         clear_bit(PAGE_CLAIMED, &page->private);
1475                 }
1476
1477                 /* We started off locked to we need to lock the pool back */
1478                 spin_lock(&pool->lock);
1479         }
1480         spin_unlock(&pool->lock);
1481         return -EAGAIN;
1482 }
1483
1484 /**
1485  * z3fold_map() - maps the allocation associated with the given handle
1486  * @pool:       pool in which the allocation resides
1487  * @handle:     handle associated with the allocation to be mapped
1488  *
1489  * Extracts the buddy number from handle and constructs the pointer to the
1490  * correct starting chunk within the page.
1491  *
1492  * Returns: a pointer to the mapped allocation
1493  */
1494 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
1495 {
1496         struct z3fold_header *zhdr;
1497         struct page *page;
1498         void *addr;
1499         enum buddy buddy;
1500
1501         zhdr = get_z3fold_header(handle);
1502         addr = zhdr;
1503         page = virt_to_page(zhdr);
1504
1505         if (test_bit(PAGE_HEADLESS, &page->private))
1506                 goto out;
1507
1508         buddy = handle_to_buddy(handle);
1509         switch (buddy) {
1510         case FIRST:
1511                 addr += ZHDR_SIZE_ALIGNED;
1512                 break;
1513         case MIDDLE:
1514                 addr += zhdr->start_middle << CHUNK_SHIFT;
1515                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1516                 break;
1517         case LAST:
1518                 addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT);
1519                 break;
1520         default:
1521                 pr_err("unknown buddy id %d\n", buddy);
1522                 WARN_ON(1);
1523                 addr = NULL;
1524                 break;
1525         }
1526
1527         if (addr)
1528                 zhdr->mapped_count++;
1529 out:
1530         put_z3fold_header(zhdr);
1531         return addr;
1532 }
1533
1534 /**
1535  * z3fold_unmap() - unmaps the allocation associated with the given handle
1536  * @pool:       pool in which the allocation resides
1537  * @handle:     handle associated with the allocation to be unmapped
1538  */
1539 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
1540 {
1541         struct z3fold_header *zhdr;
1542         struct page *page;
1543         enum buddy buddy;
1544
1545         zhdr = get_z3fold_header(handle);
1546         page = virt_to_page(zhdr);
1547
1548         if (test_bit(PAGE_HEADLESS, &page->private))
1549                 return;
1550
1551         buddy = handle_to_buddy(handle);
1552         if (buddy == MIDDLE)
1553                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1554         zhdr->mapped_count--;
1555         put_z3fold_header(zhdr);
1556 }
1557
1558 /**
1559  * z3fold_get_pool_size() - gets the z3fold pool size in pages
1560  * @pool:       pool whose size is being queried
1561  *
1562  * Returns: size in pages of the given pool.
1563  */
1564 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
1565 {
1566         return atomic64_read(&pool->pages_nr);
1567 }
1568
1569 static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
1570 {
1571         struct z3fold_header *zhdr;
1572         struct z3fold_pool *pool;
1573
1574         VM_BUG_ON_PAGE(!PageMovable(page), page);
1575         VM_BUG_ON_PAGE(PageIsolated(page), page);
1576
1577         if (test_bit(PAGE_HEADLESS, &page->private) ||
1578             test_bit(PAGE_CLAIMED, &page->private))
1579                 return false;
1580
1581         zhdr = page_address(page);
1582         z3fold_page_lock(zhdr);
1583         if (test_bit(NEEDS_COMPACTING, &page->private) ||
1584             test_bit(PAGE_STALE, &page->private))
1585                 goto out;
1586
1587         if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0)
1588                 goto out;
1589
1590         pool = zhdr_to_pool(zhdr);
1591         spin_lock(&pool->lock);
1592         if (!list_empty(&zhdr->buddy))
1593                 list_del_init(&zhdr->buddy);
1594         if (!list_empty(&page->lru))
1595                 list_del_init(&page->lru);
1596         spin_unlock(&pool->lock);
1597
1598         kref_get(&zhdr->refcount);
1599         z3fold_page_unlock(zhdr);
1600         return true;
1601
1602 out:
1603         z3fold_page_unlock(zhdr);
1604         return false;
1605 }
1606
1607 static int z3fold_page_migrate(struct address_space *mapping, struct page *newpage,
1608                                struct page *page, enum migrate_mode mode)
1609 {
1610         struct z3fold_header *zhdr, *new_zhdr;
1611         struct z3fold_pool *pool;
1612         struct address_space *new_mapping;
1613
1614         VM_BUG_ON_PAGE(!PageMovable(page), page);
1615         VM_BUG_ON_PAGE(!PageIsolated(page), page);
1616         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1617
1618         zhdr = page_address(page);
1619         pool = zhdr_to_pool(zhdr);
1620
1621         if (!z3fold_page_trylock(zhdr)) {
1622                 return -EAGAIN;
1623         }
1624         if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
1625                 z3fold_page_unlock(zhdr);
1626                 return -EBUSY;
1627         }
1628         if (work_pending(&zhdr->work)) {
1629                 z3fold_page_unlock(zhdr);
1630                 return -EAGAIN;
1631         }
1632         new_zhdr = page_address(newpage);
1633         memcpy(new_zhdr, zhdr, PAGE_SIZE);
1634         newpage->private = page->private;
1635         page->private = 0;
1636         z3fold_page_unlock(zhdr);
1637         spin_lock_init(&new_zhdr->page_lock);
1638         INIT_WORK(&new_zhdr->work, compact_page_work);
1639         /*
1640          * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
1641          * so we only have to reinitialize it.
1642          */
1643         INIT_LIST_HEAD(&new_zhdr->buddy);
1644         new_mapping = page_mapping(page);
1645         __ClearPageMovable(page);
1646         ClearPagePrivate(page);
1647
1648         get_page(newpage);
1649         z3fold_page_lock(new_zhdr);
1650         if (new_zhdr->first_chunks)
1651                 encode_handle(new_zhdr, FIRST);
1652         if (new_zhdr->last_chunks)
1653                 encode_handle(new_zhdr, LAST);
1654         if (new_zhdr->middle_chunks)
1655                 encode_handle(new_zhdr, MIDDLE);
1656         set_bit(NEEDS_COMPACTING, &newpage->private);
1657         new_zhdr->cpu = smp_processor_id();
1658         spin_lock(&pool->lock);
1659         list_add(&newpage->lru, &pool->lru);
1660         spin_unlock(&pool->lock);
1661         __SetPageMovable(newpage, new_mapping);
1662         z3fold_page_unlock(new_zhdr);
1663
1664         queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
1665
1666         page_mapcount_reset(page);
1667         put_page(page);
1668         return 0;
1669 }
1670
1671 static void z3fold_page_putback(struct page *page)
1672 {
1673         struct z3fold_header *zhdr;
1674         struct z3fold_pool *pool;
1675
1676         zhdr = page_address(page);
1677         pool = zhdr_to_pool(zhdr);
1678
1679         z3fold_page_lock(zhdr);
1680         if (!list_empty(&zhdr->buddy))
1681                 list_del_init(&zhdr->buddy);
1682         INIT_LIST_HEAD(&page->lru);
1683         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
1684                 atomic64_dec(&pool->pages_nr);
1685                 return;
1686         }
1687         spin_lock(&pool->lock);
1688         list_add(&page->lru, &pool->lru);
1689         spin_unlock(&pool->lock);
1690         z3fold_page_unlock(zhdr);
1691 }
1692
1693 static const struct address_space_operations z3fold_aops = {
1694         .isolate_page = z3fold_page_isolate,
1695         .migratepage = z3fold_page_migrate,
1696         .putback_page = z3fold_page_putback,
1697 };
1698
1699 /*****************
1700  * zpool
1701  ****************/
1702
1703 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
1704 {
1705         if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
1706                 return pool->zpool_ops->evict(pool->zpool, handle);
1707         else
1708                 return -ENOENT;
1709 }
1710
1711 static const struct z3fold_ops z3fold_zpool_ops = {
1712         .evict =        z3fold_zpool_evict
1713 };
1714
1715 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
1716                                const struct zpool_ops *zpool_ops,
1717                                struct zpool *zpool)
1718 {
1719         struct z3fold_pool *pool;
1720
1721         pool = z3fold_create_pool(name, gfp,
1722                                 zpool_ops ? &z3fold_zpool_ops : NULL);
1723         if (pool) {
1724                 pool->zpool = zpool;
1725                 pool->zpool_ops = zpool_ops;
1726         }
1727         return pool;
1728 }
1729
1730 static void z3fold_zpool_destroy(void *pool)
1731 {
1732         z3fold_destroy_pool(pool);
1733 }
1734
1735 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1736                         unsigned long *handle)
1737 {
1738         return z3fold_alloc(pool, size, gfp, handle);
1739 }
1740 static void z3fold_zpool_free(void *pool, unsigned long handle)
1741 {
1742         z3fold_free(pool, handle);
1743 }
1744
1745 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
1746                         unsigned int *reclaimed)
1747 {
1748         unsigned int total = 0;
1749         int ret = -EINVAL;
1750
1751         while (total < pages) {
1752                 ret = z3fold_reclaim_page(pool, 8);
1753                 if (ret < 0)
1754                         break;
1755                 total++;
1756         }
1757
1758         if (reclaimed)
1759                 *reclaimed = total;
1760
1761         return ret;
1762 }
1763
1764 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1765                         enum zpool_mapmode mm)
1766 {
1767         return z3fold_map(pool, handle);
1768 }
1769 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1770 {
1771         z3fold_unmap(pool, handle);
1772 }
1773
1774 static u64 z3fold_zpool_total_size(void *pool)
1775 {
1776         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1777 }
1778
1779 static struct zpool_driver z3fold_zpool_driver = {
1780         .type =         "z3fold",
1781         .owner =        THIS_MODULE,
1782         .create =       z3fold_zpool_create,
1783         .destroy =      z3fold_zpool_destroy,
1784         .malloc =       z3fold_zpool_malloc,
1785         .free =         z3fold_zpool_free,
1786         .shrink =       z3fold_zpool_shrink,
1787         .map =          z3fold_zpool_map,
1788         .unmap =        z3fold_zpool_unmap,
1789         .total_size =   z3fold_zpool_total_size,
1790 };
1791
1792 MODULE_ALIAS("zpool-z3fold");
1793
1794 static int __init init_z3fold(void)
1795 {
1796         int ret;
1797
1798         /* Make sure the z3fold header is not larger than the page size */
1799         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
1800         ret = z3fold_mount();
1801         if (ret)
1802                 return ret;
1803
1804         zpool_register_driver(&z3fold_zpool_driver);
1805
1806         return 0;
1807 }
1808
1809 static void __exit exit_z3fold(void)
1810 {
1811         z3fold_unmount();
1812         zpool_unregister_driver(&z3fold_zpool_driver);
1813 }
1814
1815 module_init(init_z3fold);
1816 module_exit(exit_z3fold);
1817
1818 MODULE_LICENSE("GPL");
1819 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1820 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");