| 1 | // SPDX-License-Identifier: GPL-2.0-only |
| 2 | /* |
| 3 | * zbud.c |
| 4 | * |
| 5 | * Copyright (C) 2013, Seth Jennings, IBM |
| 6 | * |
| 7 | * Concepts based on zcache internal zbud allocator by Dan Magenheimer. |
| 8 | * |
| 9 | * zbud is an special purpose allocator for storing compressed pages. Contrary |
| 10 | * to what its name may suggest, zbud is not a buddy allocator, but rather an |
| 11 | * allocator that "buddies" two compressed pages together in a single memory |
| 12 | * page. |
| 13 | * |
| 14 | * While this design limits storage density, it has simple and deterministic |
| 15 | * reclaim properties that make it preferable to a higher density approach when |
| 16 | * reclaim will be used. |
| 17 | * |
| 18 | * zbud works by storing compressed pages, or "zpages", together in pairs in a |
| 19 | * single memory page called a "zbud page". The first buddy is "left |
| 20 | * justified" at the beginning of the zbud page, and the last buddy is "right |
| 21 | * justified" at the end of the zbud page. The benefit is that if either |
| 22 | * buddy is freed, the freed buddy space, coalesced with whatever slack space |
| 23 | * that existed between the buddies, results in the largest possible free region |
| 24 | * within the zbud page. |
| 25 | * |
| 26 | * zbud also provides an attractive lower bound on density. The ratio of zpages |
| 27 | * to zbud pages can not be less than 1. This ensures that zbud can never "do |
| 28 | * harm" by using more pages to store zpages than the uncompressed zpages would |
| 29 | * have used on their own. |
| 30 | * |
| 31 | * zbud pages are divided into "chunks". The size of the chunks is fixed at |
| 32 | * compile time and determined by NCHUNKS_ORDER below. Dividing zbud pages |
| 33 | * into chunks allows organizing unbuddied zbud pages into a manageable number |
| 34 | * of unbuddied lists according to the number of free chunks available in the |
| 35 | * zbud page. |
| 36 | * |
| 37 | * The zbud API differs from that of conventional allocators in that the |
| 38 | * allocation function, zbud_alloc(), returns an opaque handle to the user, |
| 39 | * not a dereferenceable pointer. The user must map the handle using |
| 40 | * zbud_map() in order to get a usable pointer by which to access the |
| 41 | * allocation data and unmap the handle with zbud_unmap() when operations |
| 42 | * on the allocation data are complete. |
| 43 | */ |
| 44 | |
| 45 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| 46 | |
| 47 | #include <linux/atomic.h> |
| 48 | #include <linux/list.h> |
| 49 | #include <linux/mm.h> |
| 50 | #include <linux/module.h> |
| 51 | #include <linux/preempt.h> |
| 52 | #include <linux/slab.h> |
| 53 | #include <linux/spinlock.h> |
| 54 | #include <linux/zpool.h> |
| 55 | |
| 56 | /***************** |
| 57 | * Structures |
| 58 | *****************/ |
| 59 | /* |
| 60 | * NCHUNKS_ORDER determines the internal allocation granularity, effectively |
| 61 | * adjusting internal fragmentation. It also determines the number of |
| 62 | * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the |
| 63 | * allocation granularity will be in chunks of size PAGE_SIZE/64. As one chunk |
| 64 | * in allocated page is occupied by zbud header, NCHUNKS will be calculated to |
| 65 | * 63 which shows the max number of free chunks in zbud page, also there will be |
| 66 | * 63 freelists per pool. |
| 67 | */ |
| 68 | #define NCHUNKS_ORDER 6 |
| 69 | |
| 70 | #define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER) |
| 71 | #define CHUNK_SIZE (1 << CHUNK_SHIFT) |
| 72 | #define ZHDR_SIZE_ALIGNED CHUNK_SIZE |
| 73 | #define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT) |
| 74 | |
| 75 | struct zbud_pool; |
| 76 | |
| 77 | /** |
| 78 | * struct zbud_pool - stores metadata for each zbud pool |
| 79 | * @lock: protects all pool fields and first|last_chunk fields of any |
| 80 | * zbud page in the pool |
| 81 | * @unbuddied: array of lists tracking zbud pages that only contain one buddy; |
| 82 | * the lists each zbud page is added to depends on the size of |
| 83 | * its free region. |
| 84 | * @buddied: list tracking the zbud pages that contain two buddies; |
| 85 | * these zbud pages are full |
| 86 | * @pages_nr: number of zbud pages in the pool. |
| 87 | * |
| 88 | * This structure is allocated at pool creation time and maintains metadata |
| 89 | * pertaining to a particular zbud pool. |
| 90 | */ |
| 91 | struct zbud_pool { |
| 92 | spinlock_t lock; |
| 93 | union { |
| 94 | /* |
| 95 | * Reuse unbuddied[0] as buddied on the ground that |
| 96 | * unbuddied[0] is unused. |
| 97 | */ |
| 98 | struct list_head buddied; |
| 99 | struct list_head unbuddied[NCHUNKS]; |
| 100 | }; |
| 101 | u64 pages_nr; |
| 102 | }; |
| 103 | |
| 104 | /* |
| 105 | * struct zbud_header - zbud page metadata occupying the first chunk of each |
| 106 | * zbud page. |
| 107 | * @buddy: links the zbud page into the unbuddied/buddied lists in the pool |
| 108 | * @first_chunks: the size of the first buddy in chunks, 0 if free |
| 109 | * @last_chunks: the size of the last buddy in chunks, 0 if free |
| 110 | */ |
| 111 | struct zbud_header { |
| 112 | struct list_head buddy; |
| 113 | unsigned int first_chunks; |
| 114 | unsigned int last_chunks; |
| 115 | }; |
| 116 | |
| 117 | /***************** |
| 118 | * Helpers |
| 119 | *****************/ |
| 120 | /* Just to make the code easier to read */ |
| 121 | enum buddy { |
| 122 | FIRST, |
| 123 | LAST |
| 124 | }; |
| 125 | |
| 126 | /* Converts an allocation size in bytes to size in zbud chunks */ |
| 127 | static int size_to_chunks(size_t size) |
| 128 | { |
| 129 | return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT; |
| 130 | } |
| 131 | |
| 132 | #define for_each_unbuddied_list(_iter, _begin) \ |
| 133 | for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++) |
| 134 | |
| 135 | /* Initializes the zbud header of a newly allocated zbud page */ |
| 136 | static struct zbud_header *init_zbud_page(struct page *page) |
| 137 | { |
| 138 | struct zbud_header *zhdr = page_address(page); |
| 139 | zhdr->first_chunks = 0; |
| 140 | zhdr->last_chunks = 0; |
| 141 | INIT_LIST_HEAD(&zhdr->buddy); |
| 142 | return zhdr; |
| 143 | } |
| 144 | |
| 145 | /* Resets the struct page fields and frees the page */ |
| 146 | static void free_zbud_page(struct zbud_header *zhdr) |
| 147 | { |
| 148 | __free_page(virt_to_page(zhdr)); |
| 149 | } |
| 150 | |
| 151 | /* |
| 152 | * Encodes the handle of a particular buddy within a zbud page |
| 153 | * Pool lock should be held as this function accesses first|last_chunks |
| 154 | */ |
| 155 | static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud) |
| 156 | { |
| 157 | unsigned long handle; |
| 158 | |
| 159 | /* |
| 160 | * For now, the encoded handle is actually just the pointer to the data |
| 161 | * but this might not always be the case. A little information hiding. |
| 162 | * Add CHUNK_SIZE to the handle if it is the first allocation to jump |
| 163 | * over the zbud header in the first chunk. |
| 164 | */ |
| 165 | handle = (unsigned long)zhdr; |
| 166 | if (bud == FIRST) |
| 167 | /* skip over zbud header */ |
| 168 | handle += ZHDR_SIZE_ALIGNED; |
| 169 | else /* bud == LAST */ |
| 170 | handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT); |
| 171 | return handle; |
| 172 | } |
| 173 | |
| 174 | /* Returns the zbud page where a given handle is stored */ |
| 175 | static struct zbud_header *handle_to_zbud_header(unsigned long handle) |
| 176 | { |
| 177 | return (struct zbud_header *)(handle & PAGE_MASK); |
| 178 | } |
| 179 | |
| 180 | /* Returns the number of free chunks in a zbud page */ |
| 181 | static int num_free_chunks(struct zbud_header *zhdr) |
| 182 | { |
| 183 | /* |
| 184 | * Rather than branch for different situations, just use the fact that |
| 185 | * free buddies have a length of zero to simplify everything. |
| 186 | */ |
| 187 | return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks; |
| 188 | } |
| 189 | |
| 190 | /***************** |
| 191 | * API Functions |
| 192 | *****************/ |
| 193 | /** |
| 194 | * zbud_create_pool() - create a new zbud pool |
| 195 | * @gfp: gfp flags when allocating the zbud pool structure |
| 196 | * |
| 197 | * Return: pointer to the new zbud pool or NULL if the metadata allocation |
| 198 | * failed. |
| 199 | */ |
| 200 | static struct zbud_pool *zbud_create_pool(gfp_t gfp) |
| 201 | { |
| 202 | struct zbud_pool *pool; |
| 203 | int i; |
| 204 | |
| 205 | pool = kzalloc(sizeof(struct zbud_pool), gfp); |
| 206 | if (!pool) |
| 207 | return NULL; |
| 208 | spin_lock_init(&pool->lock); |
| 209 | for_each_unbuddied_list(i, 0) |
| 210 | INIT_LIST_HEAD(&pool->unbuddied[i]); |
| 211 | INIT_LIST_HEAD(&pool->buddied); |
| 212 | pool->pages_nr = 0; |
| 213 | return pool; |
| 214 | } |
| 215 | |
| 216 | /** |
| 217 | * zbud_destroy_pool() - destroys an existing zbud pool |
| 218 | * @pool: the zbud pool to be destroyed |
| 219 | * |
| 220 | * The pool should be emptied before this function is called. |
| 221 | */ |
| 222 | static void zbud_destroy_pool(struct zbud_pool *pool) |
| 223 | { |
| 224 | kfree(pool); |
| 225 | } |
| 226 | |
| 227 | /** |
| 228 | * zbud_alloc() - allocates a region of a given size |
| 229 | * @pool: zbud pool from which to allocate |
| 230 | * @size: size in bytes of the desired allocation |
| 231 | * @gfp: gfp flags used if the pool needs to grow |
| 232 | * @handle: handle of the new allocation |
| 233 | * |
| 234 | * This function will attempt to find a free region in the pool large enough to |
| 235 | * satisfy the allocation request. A search of the unbuddied lists is |
| 236 | * performed first. If no suitable free region is found, then a new page is |
| 237 | * allocated and added to the pool to satisfy the request. |
| 238 | * |
| 239 | * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used |
| 240 | * as zbud pool pages. |
| 241 | * |
| 242 | * Return: 0 if success and handle is set, otherwise -EINVAL if the size or |
| 243 | * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate |
| 244 | * a new page. |
| 245 | */ |
| 246 | static int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp, |
| 247 | unsigned long *handle) |
| 248 | { |
| 249 | int chunks, i, freechunks; |
| 250 | struct zbud_header *zhdr = NULL; |
| 251 | enum buddy bud; |
| 252 | struct page *page; |
| 253 | |
| 254 | if (!size || (gfp & __GFP_HIGHMEM)) |
| 255 | return -EINVAL; |
| 256 | if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE) |
| 257 | return -ENOSPC; |
| 258 | chunks = size_to_chunks(size); |
| 259 | spin_lock(&pool->lock); |
| 260 | |
| 261 | /* First, try to find an unbuddied zbud page. */ |
| 262 | for_each_unbuddied_list(i, chunks) { |
| 263 | if (!list_empty(&pool->unbuddied[i])) { |
| 264 | zhdr = list_first_entry(&pool->unbuddied[i], |
| 265 | struct zbud_header, buddy); |
| 266 | list_del(&zhdr->buddy); |
| 267 | if (zhdr->first_chunks == 0) |
| 268 | bud = FIRST; |
| 269 | else |
| 270 | bud = LAST; |
| 271 | goto found; |
| 272 | } |
| 273 | } |
| 274 | |
| 275 | /* Couldn't find unbuddied zbud page, create new one */ |
| 276 | spin_unlock(&pool->lock); |
| 277 | page = alloc_page(gfp); |
| 278 | if (!page) |
| 279 | return -ENOMEM; |
| 280 | spin_lock(&pool->lock); |
| 281 | pool->pages_nr++; |
| 282 | zhdr = init_zbud_page(page); |
| 283 | bud = FIRST; |
| 284 | |
| 285 | found: |
| 286 | if (bud == FIRST) |
| 287 | zhdr->first_chunks = chunks; |
| 288 | else |
| 289 | zhdr->last_chunks = chunks; |
| 290 | |
| 291 | if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) { |
| 292 | /* Add to unbuddied list */ |
| 293 | freechunks = num_free_chunks(zhdr); |
| 294 | list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); |
| 295 | } else { |
| 296 | /* Add to buddied list */ |
| 297 | list_add(&zhdr->buddy, &pool->buddied); |
| 298 | } |
| 299 | |
| 300 | *handle = encode_handle(zhdr, bud); |
| 301 | spin_unlock(&pool->lock); |
| 302 | |
| 303 | return 0; |
| 304 | } |
| 305 | |
| 306 | /** |
| 307 | * zbud_free() - frees the allocation associated with the given handle |
| 308 | * @pool: pool in which the allocation resided |
| 309 | * @handle: handle associated with the allocation returned by zbud_alloc() |
| 310 | */ |
| 311 | static void zbud_free(struct zbud_pool *pool, unsigned long handle) |
| 312 | { |
| 313 | struct zbud_header *zhdr; |
| 314 | int freechunks; |
| 315 | |
| 316 | spin_lock(&pool->lock); |
| 317 | zhdr = handle_to_zbud_header(handle); |
| 318 | |
| 319 | /* If first buddy, handle will be page aligned */ |
| 320 | if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK) |
| 321 | zhdr->last_chunks = 0; |
| 322 | else |
| 323 | zhdr->first_chunks = 0; |
| 324 | |
| 325 | /* Remove from existing buddy list */ |
| 326 | list_del(&zhdr->buddy); |
| 327 | |
| 328 | if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { |
| 329 | /* zbud page is empty, free */ |
| 330 | free_zbud_page(zhdr); |
| 331 | pool->pages_nr--; |
| 332 | } else { |
| 333 | /* Add to unbuddied list */ |
| 334 | freechunks = num_free_chunks(zhdr); |
| 335 | list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); |
| 336 | } |
| 337 | |
| 338 | spin_unlock(&pool->lock); |
| 339 | } |
| 340 | |
| 341 | /** |
| 342 | * zbud_map() - maps the allocation associated with the given handle |
| 343 | * @pool: pool in which the allocation resides |
| 344 | * @handle: handle associated with the allocation to be mapped |
| 345 | * |
| 346 | * While trivial for zbud, the mapping functions for others allocators |
| 347 | * implementing this allocation API could have more complex information encoded |
| 348 | * in the handle and could create temporary mappings to make the data |
| 349 | * accessible to the user. |
| 350 | * |
| 351 | * Returns: a pointer to the mapped allocation |
| 352 | */ |
| 353 | static void *zbud_map(struct zbud_pool *pool, unsigned long handle) |
| 354 | { |
| 355 | return (void *)(handle); |
| 356 | } |
| 357 | |
| 358 | /** |
| 359 | * zbud_unmap() - maps the allocation associated with the given handle |
| 360 | * @pool: pool in which the allocation resides |
| 361 | * @handle: handle associated with the allocation to be unmapped |
| 362 | */ |
| 363 | static void zbud_unmap(struct zbud_pool *pool, unsigned long handle) |
| 364 | { |
| 365 | } |
| 366 | |
| 367 | /** |
| 368 | * zbud_get_pool_pages() - gets the zbud pool size in pages |
| 369 | * @pool: pool whose size is being queried |
| 370 | * |
| 371 | * Returns: size in pages of the given pool. The pool lock need not be |
| 372 | * taken to access pages_nr. |
| 373 | */ |
| 374 | static u64 zbud_get_pool_pages(struct zbud_pool *pool) |
| 375 | { |
| 376 | return pool->pages_nr; |
| 377 | } |
| 378 | |
| 379 | /***************** |
| 380 | * zpool |
| 381 | ****************/ |
| 382 | |
| 383 | static void *zbud_zpool_create(const char *name, gfp_t gfp) |
| 384 | { |
| 385 | return zbud_create_pool(gfp); |
| 386 | } |
| 387 | |
| 388 | static void zbud_zpool_destroy(void *pool) |
| 389 | { |
| 390 | zbud_destroy_pool(pool); |
| 391 | } |
| 392 | |
| 393 | static int zbud_zpool_malloc(void *pool, size_t size, gfp_t gfp, |
| 394 | unsigned long *handle) |
| 395 | { |
| 396 | return zbud_alloc(pool, size, gfp, handle); |
| 397 | } |
| 398 | static void zbud_zpool_free(void *pool, unsigned long handle) |
| 399 | { |
| 400 | zbud_free(pool, handle); |
| 401 | } |
| 402 | |
| 403 | static void *zbud_zpool_map(void *pool, unsigned long handle, |
| 404 | enum zpool_mapmode mm) |
| 405 | { |
| 406 | return zbud_map(pool, handle); |
| 407 | } |
| 408 | static void zbud_zpool_unmap(void *pool, unsigned long handle) |
| 409 | { |
| 410 | zbud_unmap(pool, handle); |
| 411 | } |
| 412 | |
| 413 | static u64 zbud_zpool_total_pages(void *pool) |
| 414 | { |
| 415 | return zbud_get_pool_pages(pool); |
| 416 | } |
| 417 | |
| 418 | static struct zpool_driver zbud_zpool_driver = { |
| 419 | .type = "zbud", |
| 420 | .sleep_mapped = true, |
| 421 | .owner = THIS_MODULE, |
| 422 | .create = zbud_zpool_create, |
| 423 | .destroy = zbud_zpool_destroy, |
| 424 | .malloc = zbud_zpool_malloc, |
| 425 | .free = zbud_zpool_free, |
| 426 | .map = zbud_zpool_map, |
| 427 | .unmap = zbud_zpool_unmap, |
| 428 | .total_pages = zbud_zpool_total_pages, |
| 429 | }; |
| 430 | |
| 431 | MODULE_ALIAS("zpool-zbud"); |
| 432 | |
| 433 | static int __init init_zbud(void) |
| 434 | { |
| 435 | /* Make sure the zbud header will fit in one chunk */ |
| 436 | BUILD_BUG_ON(sizeof(struct zbud_header) > ZHDR_SIZE_ALIGNED); |
| 437 | pr_info("loaded\n"); |
| 438 | |
| 439 | zpool_register_driver(&zbud_zpool_driver); |
| 440 | |
| 441 | return 0; |
| 442 | } |
| 443 | |
| 444 | static void __exit exit_zbud(void) |
| 445 | { |
| 446 | zpool_unregister_driver(&zbud_zpool_driver); |
| 447 | pr_info("unloaded\n"); |
| 448 | } |
| 449 | |
| 450 | module_init(init_zbud); |
| 451 | module_exit(exit_zbud); |
| 452 | |
| 453 | MODULE_LICENSE("GPL"); |
| 454 | MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>"); |
| 455 | MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages"); |