mm/z3fold.c

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

DEFINITIONS
