mm/z3fold.c

   1 /*
   2  * z3fold.c
   3  *
   4  * Author: Vitaly Wool <vitaly.wool@konsulko.com>
   5  * Copyright (C) 2016, Sony Mobile Communications Inc.
   6  *
   7  * This implementation is based on zbud written by Seth Jennings.
   8  *
   9  * z3fold is an special purpose allocator for storing compressed pages. It
  10  * can store up to three compressed pages per page which improves the
  11  * compression ratio of zbud while retaining its main concepts (e. g. always
  12  * storing an integral number of objects per page) and simplicity.
  13  * It still has simple and deterministic reclaim properties that make it
  14  * preferable to a higher density approach (with no requirement on integral
  15  * number of object per page) when reclaim is used.
  16  *
  17  * As in zbud, pages are divided into "chunks".  The size of the chunks is
  18  * fixed at compile time and is determined by NCHUNKS_ORDER below.
  19  *
  20  * z3fold doesn't export any API and is meant to be used via zpool API.
  21  */
  22
  23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  24
  25 #include <linux/atomic.h>
  26 #include <linux/sched.h>
  27 #include <linux/list.h>
  28 #include <linux/mm.h>
  29 #include <linux/module.h>
  30 #include <linux/percpu.h>
  31 #include <linux/preempt.h>
  32 #include <linux/workqueue.h>
  33 #include <linux/slab.h>
  34 #include <linux/spinlock.h>
  35 #include <linux/zpool.h>
  36
  37 /*****************
  38  * Structures
  39 *****************/
  40 struct z3fold_pool;
  41 struct z3fold_ops {
  42         int (*evict)(struct z3fold_pool *pool, unsigned long handle);
  43 };
  44
  45 enum buddy {
  46         HEADLESS = 0,
  47         FIRST,
  48         MIDDLE,
  49         LAST,
  50         BUDDIES_MAX
  51 };
  52
  53 /*
  54  * struct z3fold_header - z3fold page metadata occupying first chunks of each
  55  *                      z3fold page, except for HEADLESS pages
  56  * @buddy:              links the z3fold page into the relevant list in the
  57  *                      pool
  58  * @page_lock:          per-page lock
  59  * @refcount:           reference count for the z3fold page
  60  * @work:               work_struct for page layout optimization
  61  * @pool:               pointer to the pool which this page belongs to
  62  * @cpu:                CPU which this page "belongs" to
  63  * @first_chunks:       the size of the first buddy in chunks, 0 if free
  64  * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
  65  * @last_chunks:        the size of the last buddy in chunks, 0 if free
  66  * @first_num:          the starting number (for the first handle)
  67  */
  68 struct z3fold_header {
  69         struct list_head buddy;
  70         spinlock_t page_lock;
  71         struct kref refcount;
  72         struct work_struct work;
  73         struct z3fold_pool *pool;
  74         short cpu;
  75         unsigned short first_chunks;
  76         unsigned short middle_chunks;
  77         unsigned short last_chunks;
  78         unsigned short start_middle;
  79         unsigned short first_num:2;
  80 };
  81
  82 /*
  83  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
  84  * adjusting internal fragmentation.  It also determines the number of
  85  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
  86  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
  87  * in the beginning of an allocated page are occupied by z3fold header, so
  88  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
  89  * which shows the max number of free chunks in z3fold page, also there will
  90  * be 63, or 62, respectively, freelists per pool.
  91  */
  92 #define NCHUNKS_ORDER   6
  93
  94 #define CHUNK_SHIFT     (PAGE_SHIFT - NCHUNKS_ORDER)
  95 #define CHUNK_SIZE      (1 << CHUNK_SHIFT)
  96 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
  97 #define ZHDR_CHUNKS     (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
  98 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
  99 #define NCHUNKS         ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
 100
 101 #define BUDDY_MASK      (0x3)
 102 #define BUDDY_SHIFT     2
 103
 104 /**
 105  * struct z3fold_pool - stores metadata for each z3fold pool
 106  * @name:       pool name
 107  * @lock:       protects pool unbuddied/lru lists
 108  * @stale_lock: protects pool stale page list
 109  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
 110  *              buddies; the list each z3fold page is added to depends on
 111  *              the size of its free region.
 112  * @lru:        list tracking the z3fold pages in LRU order by most recently
 113  *              added buddy.
 114  * @stale:      list of pages marked for freeing
 115  * @pages_nr:   number of z3fold pages in the pool.
 116  * @ops:        pointer to a structure of user defined operations specified at
 117  *              pool creation time.
 118  * @compact_wq: workqueue for page layout background optimization
 119  * @release_wq: workqueue for safe page release
 120  * @work:       work_struct for safe page release
 121  *
 122  * This structure is allocated at pool creation time and maintains metadata
 123  * pertaining to a particular z3fold pool.
 124  */
 125 struct z3fold_pool {
 126         const char *name;
 127         spinlock_t lock;
 128         spinlock_t stale_lock;
 129         struct list_head *unbuddied;
 130         struct list_head lru;
 131         struct list_head stale;
 132         atomic64_t pages_nr;
 133         const struct z3fold_ops *ops;
 134         struct zpool *zpool;
 135         const struct zpool_ops *zpool_ops;
 136         struct workqueue_struct *compact_wq;
 137         struct workqueue_struct *release_wq;
 138         struct work_struct work;
 139 };
 140
 141 /*
 142  * Internal z3fold page flags
 143  */
 144 enum z3fold_page_flags {
 145         PAGE_HEADLESS = 0,
 146         MIDDLE_CHUNK_MAPPED,
 147         NEEDS_COMPACTING,
 148         PAGE_STALE,
 149         PAGE_CLAIMED, /* by either reclaim or free */
 150 };
 151
 152 /*****************
 153  * Helpers
 154 *****************/
 155
 156 /* Converts an allocation size in bytes to size in z3fold chunks */
 157 static int size_to_chunks(size_t size)
 158 {
 159         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 160 }
 161
 162 #define for_each_unbuddied_list(_iter, _begin) \
 163         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 164
 165 static void compact_page_work(struct work_struct *w);
 166
 167 /* Initializes the z3fold header of a newly allocated z3fold page */
 168 static struct z3fold_header *init_z3fold_page(struct page *page,
 169                                         struct z3fold_pool *pool)
 170 {
 171         struct z3fold_header *zhdr = page_address(page);
 172
 173         INIT_LIST_HEAD(&page->lru);
 174         clear_bit(PAGE_HEADLESS, &page->private);
 175         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 176         clear_bit(NEEDS_COMPACTING, &page->private);
 177         clear_bit(PAGE_STALE, &page->private);
 178         clear_bit(PAGE_CLAIMED, &page->private);
 179
 180         spin_lock_init(&zhdr->page_lock);
 181         kref_init(&zhdr->refcount);
 182         zhdr->first_chunks = 0;
 183         zhdr->middle_chunks = 0;
 184         zhdr->last_chunks = 0;
 185         zhdr->first_num = 0;
 186         zhdr->start_middle = 0;
 187         zhdr->cpu = -1;
 188         zhdr->pool = pool;
 189         INIT_LIST_HEAD(&zhdr->buddy);
 190         INIT_WORK(&zhdr->work, compact_page_work);
 191         return zhdr;
 192 }
 193
 194 /* Resets the struct page fields and frees the page */
 195 static void free_z3fold_page(struct page *page)
 196 {
 197         __free_page(page);
 198 }
 199
 200 /* Lock a z3fold page */
 201 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 202 {
 203         spin_lock(&zhdr->page_lock);
 204 }
 205
 206 /* Try to lock a z3fold page */
 207 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 208 {
 209         return spin_trylock(&zhdr->page_lock);
 210 }
 211
 212 /* Unlock a z3fold page */
 213 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 214 {
 215         spin_unlock(&zhdr->page_lock);
 216 }
 217
 218 /*
 219  * Encodes the handle of a particular buddy within a z3fold page
 220  * Pool lock should be held as this function accesses first_num
 221  */
 222 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 223 {
 224         unsigned long handle;
 225
 226         handle = (unsigned long)zhdr;
 227         if (bud != HEADLESS) {
 228                 handle |= (bud + zhdr->first_num) & BUDDY_MASK;
 229                 if (bud == LAST)
 230                         handle |= (zhdr->last_chunks << BUDDY_SHIFT);
 231         }
 232         return handle;
 233 }
 234
 235 /* Returns the z3fold page where a given handle is stored */
 236 static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
 237 {
 238         return (struct z3fold_header *)(handle & PAGE_MASK);
 239 }
 240
 241 /* only for LAST bud, returns zero otherwise */
 242 static unsigned short handle_to_chunks(unsigned long handle)
 243 {
 244         return (handle & ~PAGE_MASK) >> BUDDY_SHIFT;
 245 }
 246
 247 /*
 248  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
 249  *  but that doesn't matter. because the masking will result in the
 250  *  correct buddy number.
 251  */
 252 static enum buddy handle_to_buddy(unsigned long handle)
 253 {
 254         struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
 255         return (handle - zhdr->first_num) & BUDDY_MASK;
 256 }
 257
 258 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 259 {
 260         struct page *page = virt_to_page(zhdr);
 261         struct z3fold_pool *pool = zhdr->pool;
 262
 263         WARN_ON(!list_empty(&zhdr->buddy));
 264         set_bit(PAGE_STALE, &page->private);
 265         clear_bit(NEEDS_COMPACTING, &page->private);
 266         spin_lock(&pool->lock);
 267         if (!list_empty(&page->lru))
 268                 list_del(&page->lru);
 269         spin_unlock(&pool->lock);
 270         if (locked)
 271                 z3fold_page_unlock(zhdr);
 272         spin_lock(&pool->stale_lock);
 273         list_add(&zhdr->buddy, &pool->stale);
 274         queue_work(pool->release_wq, &pool->work);
 275         spin_unlock(&pool->stale_lock);
 276 }
 277
 278 static void __attribute__((__unused__))
 279                         release_z3fold_page(struct kref *ref)
 280 {
 281         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 282                                                 refcount);
 283         __release_z3fold_page(zhdr, false);
 284 }
 285
 286 static void release_z3fold_page_locked(struct kref *ref)
 287 {
 288         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 289                                                 refcount);
 290         WARN_ON(z3fold_page_trylock(zhdr));
 291         __release_z3fold_page(zhdr, true);
 292 }
 293
 294 static void release_z3fold_page_locked_list(struct kref *ref)
 295 {
 296         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 297                                                refcount);
 298         spin_lock(&zhdr->pool->lock);
 299         list_del_init(&zhdr->buddy);
 300         spin_unlock(&zhdr->pool->lock);
 301
 302         WARN_ON(z3fold_page_trylock(zhdr));
 303         __release_z3fold_page(zhdr, true);
 304 }
 305
 306 static void free_pages_work(struct work_struct *w)
 307 {
 308         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 309
 310         spin_lock(&pool->stale_lock);
 311         while (!list_empty(&pool->stale)) {
 312                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
 313                                                 struct z3fold_header, buddy);
 314                 struct page *page = virt_to_page(zhdr);
 315
 316                 list_del(&zhdr->buddy);
 317                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
 318                         continue;
 319                 spin_unlock(&pool->stale_lock);
 320                 cancel_work_sync(&zhdr->work);
 321                 free_z3fold_page(page);
 322                 cond_resched();
 323                 spin_lock(&pool->stale_lock);
 324         }
 325         spin_unlock(&pool->stale_lock);
 326 }
 327
 328 /*
 329  * Returns the number of free chunks in a z3fold page.
 330  * NB: can't be used with HEADLESS pages.
 331  */
 332 static int num_free_chunks(struct z3fold_header *zhdr)
 333 {
 334         int nfree;
 335         /*
 336          * If there is a middle object, pick up the bigger free space
 337          * either before or after it. Otherwise just subtract the number
 338          * of chunks occupied by the first and the last objects.
 339          */
 340         if (zhdr->middle_chunks != 0) {
 341                 int nfree_before = zhdr->first_chunks ?
 342                         0 : zhdr->start_middle - ZHDR_CHUNKS;
 343                 int nfree_after = zhdr->last_chunks ?
 344                         0 : TOTAL_CHUNKS -
 345                                 (zhdr->start_middle + zhdr->middle_chunks);
 346                 nfree = max(nfree_before, nfree_after);
 347         } else
 348                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
 349         return nfree;
 350 }
 351
 352 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 353                                 unsigned short dst_chunk)
 354 {
 355         void *beg = zhdr;
 356         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
 357                        beg + (zhdr->start_middle << CHUNK_SHIFT),
 358                        zhdr->middle_chunks << CHUNK_SHIFT);
 359 }
 360
 361 #define BIG_CHUNK_GAP   3
 362 /* Has to be called with lock held */
 363 static int z3fold_compact_page(struct z3fold_header *zhdr)
 364 {
 365         struct page *page = virt_to_page(zhdr);
 366
 367         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 368                 return 0; /* can't move middle chunk, it's used */
 369
 370         if (zhdr->middle_chunks == 0)
 371                 return 0; /* nothing to compact */
 372
 373         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
 374                 /* move to the beginning */
 375                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
 376                 zhdr->first_chunks = zhdr->middle_chunks;
 377                 zhdr->middle_chunks = 0;
 378                 zhdr->start_middle = 0;
 379                 zhdr->first_num++;
 380                 return 1;
 381         }
 382
 383         /*
 384          * moving data is expensive, so let's only do that if
 385          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
 386          */
 387         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
 388             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
 389                         BIG_CHUNK_GAP) {
 390                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
 391                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 392                 return 1;
 393         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
 394                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
 395                                         + zhdr->middle_chunks) >=
 396                         BIG_CHUNK_GAP) {
 397                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
 398                         zhdr->middle_chunks;
 399                 mchunk_memmove(zhdr, new_start);
 400                 zhdr->start_middle = new_start;
 401                 return 1;
 402         }
 403
 404         return 0;
 405 }
 406
 407 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 408 {
 409         struct z3fold_pool *pool = zhdr->pool;
 410         struct page *page;
 411         struct list_head *unbuddied;
 412         int fchunks;
 413
 414         page = virt_to_page(zhdr);
 415         if (locked)
 416                 WARN_ON(z3fold_page_trylock(zhdr));
 417         else
 418                 z3fold_page_lock(zhdr);
 419         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
 420                 z3fold_page_unlock(zhdr);
 421                 return;
 422         }
 423         spin_lock(&pool->lock);
 424         list_del_init(&zhdr->buddy);
 425         spin_unlock(&pool->lock);
 426
 427         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
 428                 atomic64_dec(&pool->pages_nr);
 429                 return;
 430         }
 431
 432         z3fold_compact_page(zhdr);
 433         unbuddied = get_cpu_ptr(pool->unbuddied);
 434         fchunks = num_free_chunks(zhdr);
 435         if (fchunks < NCHUNKS &&
 436             (!zhdr->first_chunks || !zhdr->middle_chunks ||
 437                         !zhdr->last_chunks)) {
 438                 /* the page's not completely free and it's unbuddied */
 439                 spin_lock(&pool->lock);
 440                 list_add(&zhdr->buddy, &unbuddied[fchunks]);
 441                 spin_unlock(&pool->lock);
 442                 zhdr->cpu = smp_processor_id();
 443         }
 444         put_cpu_ptr(pool->unbuddied);
 445         z3fold_page_unlock(zhdr);
 446 }
 447
 448 static void compact_page_work(struct work_struct *w)
 449 {
 450         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
 451                                                 work);
 452
 453         do_compact_page(zhdr, false);
 454 }
 455
 456
 457 /*
 458  * API Functions
 459  */
 460
 461 /**
 462  * z3fold_create_pool() - create a new z3fold pool
 463  * @name:       pool name
 464  * @gfp:        gfp flags when allocating the z3fold pool structure
 465  * @ops:        user-defined operations for the z3fold pool
 466  *
 467  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
 468  * failed.
 469  */
 470 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
 471                 const struct z3fold_ops *ops)
 472 {
 473         struct z3fold_pool *pool = NULL;
 474         int i, cpu;
 475
 476         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
 477         if (!pool)
 478                 goto out;
 479         spin_lock_init(&pool->lock);
 480         spin_lock_init(&pool->stale_lock);
 481         pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
 482         if (!pool->unbuddied)
 483                 goto out_pool;
 484         for_each_possible_cpu(cpu) {
 485                 struct list_head *unbuddied =
 486                                 per_cpu_ptr(pool->unbuddied, cpu);
 487                 for_each_unbuddied_list(i, 0)
 488                         INIT_LIST_HEAD(&unbuddied[i]);
 489         }
 490         INIT_LIST_HEAD(&pool->lru);
 491         INIT_LIST_HEAD(&pool->stale);
 492         atomic64_set(&pool->pages_nr, 0);
 493         pool->name = name;
 494         pool->compact_wq = create_singlethread_workqueue(pool->name);
 495         if (!pool->compact_wq)
 496                 goto out_unbuddied;
 497         pool->release_wq = create_singlethread_workqueue(pool->name);
 498         if (!pool->release_wq)
 499                 goto out_wq;
 500         INIT_WORK(&pool->work, free_pages_work);
 501         pool->ops = ops;
 502         return pool;
 503
 504 out_wq:
 505         destroy_workqueue(pool->compact_wq);
 506 out_unbuddied:
 507         free_percpu(pool->unbuddied);
 508 out_pool:
 509         kfree(pool);
 510 out:
 511         return NULL;
 512 }
 513
 514 /**
 515  * z3fold_destroy_pool() - destroys an existing z3fold pool
 516  * @pool:       the z3fold pool to be destroyed
 517  *
 518  * The pool should be emptied before this function is called.
 519  */
 520 static void z3fold_destroy_pool(struct z3fold_pool *pool)
 521 {
 522         destroy_workqueue(pool->release_wq);
 523         destroy_workqueue(pool->compact_wq);
 524         kfree(pool);
 525 }
 526
 527 /**
 528  * z3fold_alloc() - allocates a region of a given size
 529  * @pool:       z3fold pool from which to allocate
 530  * @size:       size in bytes of the desired allocation
 531  * @gfp:        gfp flags used if the pool needs to grow
 532  * @handle:     handle of the new allocation
 533  *
 534  * This function will attempt to find a free region in the pool large enough to
 535  * satisfy the allocation request.  A search of the unbuddied lists is
 536  * performed first. If no suitable free region is found, then a new page is
 537  * allocated and added to the pool to satisfy the request.
 538  *
 539  * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
 540  * as z3fold pool pages.
 541  *
 542  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
 543  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
 544  * a new page.
 545  */
 546 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 547                         unsigned long *handle)
 548 {
 549         int chunks = 0, i, freechunks;
 550         struct z3fold_header *zhdr = NULL;
 551         struct page *page = NULL;
 552         enum buddy bud;
 553         bool can_sleep = (gfp & __GFP_RECLAIM) == __GFP_RECLAIM;
 554
 555         if (!size || (gfp & __GFP_HIGHMEM))
 556                 return -EINVAL;
 557
 558         if (size > PAGE_SIZE)
 559                 return -ENOSPC;
 560
 561         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
 562                 bud = HEADLESS;
 563         else {
 564                 struct list_head *unbuddied;
 565                 chunks = size_to_chunks(size);
 566
 567 lookup:
 568                 /* First, try to find an unbuddied z3fold page. */
 569                 unbuddied = get_cpu_ptr(pool->unbuddied);
 570                 for_each_unbuddied_list(i, chunks) {
 571                         struct list_head *l = &unbuddied[i];
 572
 573                         zhdr = list_first_entry_or_null(READ_ONCE(l),
 574                                                 struct z3fold_header, buddy);
 575
 576                         if (!zhdr)
 577                                 continue;
 578
 579                         /* Re-check under lock. */
 580                         spin_lock(&pool->lock);
 581                         l = &unbuddied[i];
 582                         if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
 583                                         struct z3fold_header, buddy)) ||
 584                             !z3fold_page_trylock(zhdr)) {
 585                                 spin_unlock(&pool->lock);
 586                                 put_cpu_ptr(pool->unbuddied);
 587                                 goto lookup;
 588                         }
 589                         list_del_init(&zhdr->buddy);
 590                         zhdr->cpu = -1;
 591                         spin_unlock(&pool->lock);
 592
 593                         page = virt_to_page(zhdr);
 594                         if (test_bit(NEEDS_COMPACTING, &page->private)) {
 595                                 z3fold_page_unlock(zhdr);
 596                                 zhdr = NULL;
 597                                 put_cpu_ptr(pool->unbuddied);
 598                                 if (can_sleep)
 599                                         cond_resched();
 600                                 goto lookup;
 601                         }
 602
 603                         /*
 604                          * this page could not be removed from its unbuddied
 605                          * list while pool lock was held, and then we've taken
 606                          * page lock so kref_put could not be called before
 607                          * we got here, so it's safe to just call kref_get()
 608                          */
 609                         kref_get(&zhdr->refcount);
 610                         break;
 611                 }
 612                 put_cpu_ptr(pool->unbuddied);
 613
 614                 if (zhdr) {
 615                         if (zhdr->first_chunks == 0) {
 616                                 if (zhdr->middle_chunks != 0 &&
 617                                     chunks >= zhdr->start_middle)
 618                                         bud = LAST;
 619                                 else
 620                                         bud = FIRST;
 621                         } else if (zhdr->last_chunks == 0)
 622                                 bud = LAST;
 623                         else if (zhdr->middle_chunks == 0)
 624                                 bud = MIDDLE;
 625                         else {
 626                                 if (kref_put(&zhdr->refcount,
 627                                              release_z3fold_page_locked))
 628                                         atomic64_dec(&pool->pages_nr);
 629                                 else
 630                                         z3fold_page_unlock(zhdr);
 631                                 pr_err("No free chunks in unbuddied\n");
 632                                 WARN_ON(1);
 633                                 goto lookup;
 634                         }
 635                         goto found;
 636                 }
 637                 bud = FIRST;
 638         }
 639
 640         spin_lock(&pool->stale_lock);
 641         zhdr = list_first_entry_or_null(&pool->stale,
 642                                         struct z3fold_header, buddy);
 643         /*
 644          * Before allocating a page, let's see if we can take one from the
 645          * stale pages list. cancel_work_sync() can sleep so we must make
 646          * sure it won't be called in case we're in atomic context.
 647          */
 648         if (zhdr && (can_sleep || !work_pending(&zhdr->work))) {
 649                 list_del(&zhdr->buddy);
 650                 spin_unlock(&pool->stale_lock);
 651                 if (can_sleep)
 652                         cancel_work_sync(&zhdr->work);
 653                 page = virt_to_page(zhdr);
 654         } else {
 655                 spin_unlock(&pool->stale_lock);
 656                 page = alloc_page(gfp);
 657         }
 658
 659         if (!page)
 660                 return -ENOMEM;
 661
 662         atomic64_inc(&pool->pages_nr);
 663         zhdr = init_z3fold_page(page, pool);
 664
 665         if (bud == HEADLESS) {
 666                 set_bit(PAGE_HEADLESS, &page->private);
 667                 goto headless;
 668         }
 669         z3fold_page_lock(zhdr);
 670
 671 found:
 672         if (bud == FIRST)
 673                 zhdr->first_chunks = chunks;
 674         else if (bud == LAST)
 675                 zhdr->last_chunks = chunks;
 676         else {
 677                 zhdr->middle_chunks = chunks;
 678                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
 679         }
 680
 681         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 682                         zhdr->middle_chunks == 0) {
 683                 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
 684
 685                 /* Add to unbuddied list */
 686                 freechunks = num_free_chunks(zhdr);
 687                 spin_lock(&pool->lock);
 688                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
 689                 spin_unlock(&pool->lock);
 690                 zhdr->cpu = smp_processor_id();
 691                 put_cpu_ptr(pool->unbuddied);
 692         }
 693
 694 headless:
 695         spin_lock(&pool->lock);
 696         /* Add/move z3fold page to beginning of LRU */
 697         if (!list_empty(&page->lru))
 698                 list_del(&page->lru);
 699
 700         list_add(&page->lru, &pool->lru);
 701
 702         *handle = encode_handle(zhdr, bud);
 703         spin_unlock(&pool->lock);
 704         if (bud != HEADLESS)
 705                 z3fold_page_unlock(zhdr);
 706
 707         return 0;
 708 }
 709
 710 /**
 711  * z3fold_free() - frees the allocation associated with the given handle
 712  * @pool:       pool in which the allocation resided
 713  * @handle:     handle associated with the allocation returned by z3fold_alloc()
 714  *
 715  * In the case that the z3fold page in which the allocation resides is under
 716  * reclaim, as indicated by the PG_reclaim flag being set, this function
 717  * only sets the first|last_chunks to 0.  The page is actually freed
 718  * once both buddies are evicted (see z3fold_reclaim_page() below).
 719  */
 720 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 721 {
 722         struct z3fold_header *zhdr;
 723         struct page *page;
 724         enum buddy bud;
 725
 726         zhdr = handle_to_z3fold_header(handle);
 727         page = virt_to_page(zhdr);
 728
 729         if (test_bit(PAGE_HEADLESS, &page->private)) {
 730                 /* if a headless page is under reclaim, just leave.
 731                  * NB: we use test_and_set_bit for a reason: if the bit
 732                  * has not been set before, we release this page
 733                  * immediately so we don't care about its value any more.
 734                  */
 735                 if (!test_and_set_bit(PAGE_CLAIMED, &page->private)) {
 736                         spin_lock(&pool->lock);
 737                         list_del(&page->lru);
 738                         spin_unlock(&pool->lock);
 739                         free_z3fold_page(page);
 740                         atomic64_dec(&pool->pages_nr);
 741                 }
 742                 return;
 743         }
 744
 745         /* Non-headless case */
 746         z3fold_page_lock(zhdr);
 747         bud = handle_to_buddy(handle);
 748
 749         switch (bud) {
 750         case FIRST:
 751                 zhdr->first_chunks = 0;
 752                 break;
 753         case MIDDLE:
 754                 zhdr->middle_chunks = 0;
 755                 break;
 756         case LAST:
 757                 zhdr->last_chunks = 0;
 758                 break;
 759         default:
 760                 pr_err("%s: unknown bud %d\n", __func__, bud);
 761                 WARN_ON(1);
 762                 z3fold_page_unlock(zhdr);
 763                 return;
 764         }
 765
 766         if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 767                 atomic64_dec(&pool->pages_nr);
 768                 return;
 769         }
 770         if (test_bit(PAGE_CLAIMED, &page->private)) {
 771                 z3fold_page_unlock(zhdr);
 772                 return;
 773         }
 774         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
 775                 z3fold_page_unlock(zhdr);
 776                 return;
 777         }
 778         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
 779                 spin_lock(&pool->lock);
 780                 list_del_init(&zhdr->buddy);
 781                 spin_unlock(&pool->lock);
 782                 zhdr->cpu = -1;
 783                 kref_get(&zhdr->refcount);
 784                 do_compact_page(zhdr, true);
 785                 return;
 786         }
 787         kref_get(&zhdr->refcount);
 788         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
 789         z3fold_page_unlock(zhdr);
 790 }
 791
 792 /**
 793  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
 794  * @pool:       pool from which a page will attempt to be evicted
 795  * @retires:    number of pages on the LRU list for which eviction will
 796  *              be attempted before failing
 797  *
 798  * z3fold reclaim is different from normal system reclaim in that it is done
 799  * from the bottom, up. This is because only the bottom layer, z3fold, has
 800  * information on how the allocations are organized within each z3fold page.
 801  * This has the potential to create interesting locking situations between
 802  * z3fold and the user, however.
 803  *
 804  * To avoid these, this is how z3fold_reclaim_page() should be called:
 805
 806  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
 807  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
 808  * call the user-defined eviction handler with the pool and handle as
 809  * arguments.
 810  *
 811  * If the handle can not be evicted, the eviction handler should return
 812  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
 813  * appropriate list and try the next z3fold page on the LRU up to
 814  * a user defined number of retries.
 815  *
 816  * If the handle is successfully evicted, the eviction handler should
 817  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
 818  * contains logic to delay freeing the page if the page is under reclaim,
 819  * as indicated by the setting of the PG_reclaim flag on the underlying page.
 820  *
 821  * If all buddies in the z3fold page are successfully evicted, then the
 822  * z3fold page can be freed.
 823  *
 824  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
 825  * no pages to evict or an eviction handler is not registered, -EAGAIN if
 826  * the retry limit was hit.
 827  */
 828 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 829 {
 830         int i, ret = 0;
 831         struct z3fold_header *zhdr = NULL;
 832         struct page *page = NULL;
 833         struct list_head *pos;
 834         unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
 835
 836         spin_lock(&pool->lock);
 837         if (!pool->ops || !pool->ops->evict || retries == 0) {
 838                 spin_unlock(&pool->lock);
 839                 return -EINVAL;
 840         }
 841         for (i = 0; i < retries; i++) {
 842                 if (list_empty(&pool->lru)) {
 843                         spin_unlock(&pool->lock);
 844                         return -EINVAL;
 845                 }
 846                 list_for_each_prev(pos, &pool->lru) {
 847                         page = list_entry(pos, struct page, lru);
 848
 849                         /* this bit could have been set by free, in which case
 850                          * we pass over to the next page in the pool.
 851                          */
 852                         if (test_and_set_bit(PAGE_CLAIMED, &page->private))
 853                                 continue;
 854
 855                         zhdr = page_address(page);
 856                         if (test_bit(PAGE_HEADLESS, &page->private))
 857                                 break;
 858
 859                         if (!z3fold_page_trylock(zhdr)) {
 860                                 zhdr = NULL;
 861                                 continue; /* can't evict at this point */
 862                         }
 863                         kref_get(&zhdr->refcount);
 864                         list_del_init(&zhdr->buddy);
 865                         zhdr->cpu = -1;
 866                         break;
 867                 }
 868
 869                 if (!zhdr)
 870                         break;
 871
 872                 list_del_init(&page->lru);
 873                 spin_unlock(&pool->lock);
 874
 875                 if (!test_bit(PAGE_HEADLESS, &page->private)) {
 876                         /*
 877                          * We need encode the handles before unlocking, since
 878                          * we can race with free that will set
 879                          * (first|last)_chunks to 0
 880                          */
 881                         first_handle = 0;
 882                         last_handle = 0;
 883                         middle_handle = 0;
 884                         if (zhdr->first_chunks)
 885                                 first_handle = encode_handle(zhdr, FIRST);
 886                         if (zhdr->middle_chunks)
 887                                 middle_handle = encode_handle(zhdr, MIDDLE);
 888                         if (zhdr->last_chunks)
 889                                 last_handle = encode_handle(zhdr, LAST);
 890                         /*
 891                          * it's safe to unlock here because we hold a
 892                          * reference to this page
 893                          */
 894                         z3fold_page_unlock(zhdr);
 895                 } else {
 896                         first_handle = encode_handle(zhdr, HEADLESS);
 897                         last_handle = middle_handle = 0;
 898                 }
 899
 900                 /* Issue the eviction callback(s) */
 901                 if (middle_handle) {
 902                         ret = pool->ops->evict(pool, middle_handle);
 903                         if (ret)
 904                                 goto next;
 905                 }
 906                 if (first_handle) {
 907                         ret = pool->ops->evict(pool, first_handle);
 908                         if (ret)
 909                                 goto next;
 910                 }
 911                 if (last_handle) {
 912                         ret = pool->ops->evict(pool, last_handle);
 913                         if (ret)
 914                                 goto next;
 915                 }
 916 next:
 917                 if (test_bit(PAGE_HEADLESS, &page->private)) {
 918                         if (ret == 0) {
 919                                 free_z3fold_page(page);
 920                                 atomic64_dec(&pool->pages_nr);
 921                                 return 0;
 922                         }
 923                         spin_lock(&pool->lock);
 924                         list_add(&page->lru, &pool->lru);
 925                         spin_unlock(&pool->lock);
 926                 } else {
 927                         z3fold_page_lock(zhdr);
 928                         clear_bit(PAGE_CLAIMED, &page->private);
 929                         if (kref_put(&zhdr->refcount,
 930                                         release_z3fold_page_locked)) {
 931                                 atomic64_dec(&pool->pages_nr);
 932                                 return 0;
 933                         }
 934                         /*
 935                          * if we are here, the page is still not completely
 936                          * free. Take the global pool lock then to be able
 937                          * to add it back to the lru list
 938                          */
 939                         spin_lock(&pool->lock);
 940                         list_add(&page->lru, &pool->lru);
 941                         spin_unlock(&pool->lock);
 942                         z3fold_page_unlock(zhdr);
 943                 }
 944
 945                 /* We started off locked to we need to lock the pool back */
 946                 spin_lock(&pool->lock);
 947         }
 948         spin_unlock(&pool->lock);
 949         return -EAGAIN;
 950 }
 951
 952 /**
 953  * z3fold_map() - maps the allocation associated with the given handle
 954  * @pool:       pool in which the allocation resides
 955  * @handle:     handle associated with the allocation to be mapped
 956  *
 957  * Extracts the buddy number from handle and constructs the pointer to the
 958  * correct starting chunk within the page.
 959  *
 960  * Returns: a pointer to the mapped allocation
 961  */
 962 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
 963 {
 964         struct z3fold_header *zhdr;
 965         struct page *page;
 966         void *addr;
 967         enum buddy buddy;
 968
 969         zhdr = handle_to_z3fold_header(handle);
 970         addr = zhdr;
 971         page = virt_to_page(zhdr);
 972
 973         if (test_bit(PAGE_HEADLESS, &page->private))
 974                 goto out;
 975
 976         z3fold_page_lock(zhdr);
 977         buddy = handle_to_buddy(handle);
 978         switch (buddy) {
 979         case FIRST:
 980                 addr += ZHDR_SIZE_ALIGNED;
 981                 break;
 982         case MIDDLE:
 983                 addr += zhdr->start_middle << CHUNK_SHIFT;
 984                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 985                 break;
 986         case LAST:
 987                 addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT);
 988                 break;
 989         default:
 990                 pr_err("unknown buddy id %d\n", buddy);
 991                 WARN_ON(1);
 992                 addr = NULL;
 993                 break;
 994         }
 995
 996         z3fold_page_unlock(zhdr);
 997 out:
 998         return addr;
 999 }
1000
1001 /**
1002  * z3fold_unmap() - unmaps the allocation associated with the given handle
1003  * @pool:       pool in which the allocation resides
1004  * @handle:     handle associated with the allocation to be unmapped
1005  */
1006 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
1007 {
1008         struct z3fold_header *zhdr;
1009         struct page *page;
1010         enum buddy buddy;
1011
1012         zhdr = handle_to_z3fold_header(handle);
1013         page = virt_to_page(zhdr);
1014
1015         if (test_bit(PAGE_HEADLESS, &page->private))
1016                 return;
1017
1018         z3fold_page_lock(zhdr);
1019         buddy = handle_to_buddy(handle);
1020         if (buddy == MIDDLE)
1021                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1022         z3fold_page_unlock(zhdr);
1023 }
1024
1025 /**
1026  * z3fold_get_pool_size() - gets the z3fold pool size in pages
1027  * @pool:       pool whose size is being queried
1028  *
1029  * Returns: size in pages of the given pool.
1030  */
1031 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
1032 {
1033         return atomic64_read(&pool->pages_nr);
1034 }
1035
1036 /*****************
1037  * zpool
1038  ****************/
1039
1040 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
1041 {
1042         if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
1043                 return pool->zpool_ops->evict(pool->zpool, handle);
1044         else
1045                 return -ENOENT;
1046 }
1047
1048 static const struct z3fold_ops z3fold_zpool_ops = {
1049         .evict =        z3fold_zpool_evict
1050 };
1051
1052 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
1053                                const struct zpool_ops *zpool_ops,
1054                                struct zpool *zpool)
1055 {
1056         struct z3fold_pool *pool;
1057
1058         pool = z3fold_create_pool(name, gfp,
1059                                 zpool_ops ? &z3fold_zpool_ops : NULL);
1060         if (pool) {
1061                 pool->zpool = zpool;
1062                 pool->zpool_ops = zpool_ops;
1063         }
1064         return pool;
1065 }
1066
1067 static void z3fold_zpool_destroy(void *pool)
1068 {
1069         z3fold_destroy_pool(pool);
1070 }
1071
1072 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1073                         unsigned long *handle)
1074 {
1075         return z3fold_alloc(pool, size, gfp, handle);
1076 }
1077 static void z3fold_zpool_free(void *pool, unsigned long handle)
1078 {
1079         z3fold_free(pool, handle);
1080 }
1081
1082 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
1083                         unsigned int *reclaimed)
1084 {
1085         unsigned int total = 0;
1086         int ret = -EINVAL;
1087
1088         while (total < pages) {
1089                 ret = z3fold_reclaim_page(pool, 8);
1090                 if (ret < 0)
1091                         break;
1092                 total++;
1093         }
1094
1095         if (reclaimed)
1096                 *reclaimed = total;
1097
1098         return ret;
1099 }
1100
1101 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1102                         enum zpool_mapmode mm)
1103 {
1104         return z3fold_map(pool, handle);
1105 }
1106 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1107 {
1108         z3fold_unmap(pool, handle);
1109 }
1110
1111 static u64 z3fold_zpool_total_size(void *pool)
1112 {
1113         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1114 }
1115
1116 static struct zpool_driver z3fold_zpool_driver = {
1117         .type =         "z3fold",
1118         .owner =        THIS_MODULE,
1119         .create =       z3fold_zpool_create,
1120         .destroy =      z3fold_zpool_destroy,
1121         .malloc =       z3fold_zpool_malloc,
1122         .free =         z3fold_zpool_free,
1123         .shrink =       z3fold_zpool_shrink,
1124         .map =          z3fold_zpool_map,
1125         .unmap =        z3fold_zpool_unmap,
1126         .total_size =   z3fold_zpool_total_size,
1127 };
1128
1129 MODULE_ALIAS("zpool-z3fold");
1130
1131 static int __init init_z3fold(void)
1132 {
1133         /* Make sure the z3fold header is not larger than the page size */
1134         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
1135         zpool_register_driver(&z3fold_zpool_driver);
1136
1137         return 0;
1138 }
1139
1140 static void __exit exit_z3fold(void)
1141 {
1142         zpool_unregister_driver(&z3fold_zpool_driver);
1143 }
1144
1145 module_init(init_z3fold);
1146 module_exit(exit_z3fold);
1147
1148 MODULE_LICENSE("GPL");
1149 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1150 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");