linux/mm/slob.c
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   1/*
   2 * SLOB Allocator: Simple List Of Blocks
   3 *
   4 * Matt Mackall <mpm@selenic.com> 12/30/03
   5 *
   6 * NUMA support by Paul Mundt, 2007.
   7 *
   8 * How SLOB works:
   9 *
  10 * The core of SLOB is a traditional K&R style heap allocator, with
  11 * support for returning aligned objects. The granularity of this
  12 * allocator is as little as 2 bytes, however typically most architectures
  13 * will require 4 bytes on 32-bit and 8 bytes on 64-bit.
  14 *
  15 * The slob heap is a set of linked list of pages from alloc_pages(),
  16 * and within each page, there is a singly-linked list of free blocks
  17 * (slob_t). The heap is grown on demand. To reduce fragmentation,
  18 * heap pages are segregated into three lists, with objects less than
  19 * 256 bytes, objects less than 1024 bytes, and all other objects.
  20 *
  21 * Allocation from heap involves first searching for a page with
  22 * sufficient free blocks (using a next-fit-like approach) followed by
  23 * a first-fit scan of the page. Deallocation inserts objects back
  24 * into the free list in address order, so this is effectively an
  25 * address-ordered first fit.
  26 *
  27 * Above this is an implementation of kmalloc/kfree. Blocks returned
  28 * from kmalloc are prepended with a 4-byte header with the kmalloc size.
  29 * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
  30 * alloc_pages() directly, allocating compound pages so the page order
  31 * does not have to be separately tracked, and also stores the exact
  32 * allocation size in page->private so that it can be used to accurately
  33 * provide ksize(). These objects are detected in kfree() because slob_page()
  34 * is false for them.
  35 *
  36 * SLAB is emulated on top of SLOB by simply calling constructors and
  37 * destructors for every SLAB allocation. Objects are returned with the
  38 * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
  39 * case the low-level allocator will fragment blocks to create the proper
  40 * alignment. Again, objects of page-size or greater are allocated by
  41 * calling alloc_pages(). As SLAB objects know their size, no separate
  42 * size bookkeeping is necessary and there is essentially no allocation
  43 * space overhead, and compound pages aren't needed for multi-page
  44 * allocations.
  45 *
  46 * NUMA support in SLOB is fairly simplistic, pushing most of the real
  47 * logic down to the page allocator, and simply doing the node accounting
  48 * on the upper levels. In the event that a node id is explicitly
  49 * provided, alloc_pages_exact_node() with the specified node id is used
  50 * instead. The common case (or when the node id isn't explicitly provided)
  51 * will default to the current node, as per numa_node_id().
  52 *
  53 * Node aware pages are still inserted in to the global freelist, and
  54 * these are scanned for by matching against the node id encoded in the
  55 * page flags. As a result, block allocations that can be satisfied from
  56 * the freelist will only be done so on pages residing on the same node,
  57 * in order to prevent random node placement.
  58 */
  59
  60#include <linux/kernel.h>
  61#include <linux/slab.h>
  62#include "slab.h"
  63
  64#include <linux/mm.h>
  65#include <linux/swap.h> /* struct reclaim_state */
  66#include <linux/cache.h>
  67#include <linux/init.h>
  68#include <linux/export.h>
  69#include <linux/rcupdate.h>
  70#include <linux/list.h>
  71#include <linux/kmemleak.h>
  72
  73#include <trace/events/kmem.h>
  74
  75#include <linux/atomic.h>
  76
  77/*
  78 * slob_block has a field 'units', which indicates size of block if +ve,
  79 * or offset of next block if -ve (in SLOB_UNITs).
  80 *
  81 * Free blocks of size 1 unit simply contain the offset of the next block.
  82 * Those with larger size contain their size in the first SLOB_UNIT of
  83 * memory, and the offset of the next free block in the second SLOB_UNIT.
  84 */
  85#if PAGE_SIZE <= (32767 * 2)
  86typedef s16 slobidx_t;
  87#else
  88typedef s32 slobidx_t;
  89#endif
  90
  91struct slob_block {
  92        slobidx_t units;
  93};
  94typedef struct slob_block slob_t;
  95
  96/*
  97 * All partially free slob pages go on these lists.
  98 */
  99#define SLOB_BREAK1 256
 100#define SLOB_BREAK2 1024
 101static LIST_HEAD(free_slob_small);
 102static LIST_HEAD(free_slob_medium);
 103static LIST_HEAD(free_slob_large);
 104
 105/*
 106 * slob_page_free: true for pages on free_slob_pages list.
 107 */
 108static inline int slob_page_free(struct page *sp)
 109{
 110        return PageSlobFree(sp);
 111}
 112
 113static void set_slob_page_free(struct page *sp, struct list_head *list)
 114{
 115        list_add(&sp->list, list);
 116        __SetPageSlobFree(sp);
 117}
 118
 119static inline void clear_slob_page_free(struct page *sp)
 120{
 121        list_del(&sp->list);
 122        __ClearPageSlobFree(sp);
 123}
 124
 125#define SLOB_UNIT sizeof(slob_t)
 126#define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
 127#define SLOB_ALIGN L1_CACHE_BYTES
 128
 129/*
 130 * struct slob_rcu is inserted at the tail of allocated slob blocks, which
 131 * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
 132 * the block using call_rcu.
 133 */
 134struct slob_rcu {
 135        struct rcu_head head;
 136        int size;
 137};
 138
 139/*
 140 * slob_lock protects all slob allocator structures.
 141 */
 142static DEFINE_SPINLOCK(slob_lock);
 143
 144/*
 145 * Encode the given size and next info into a free slob block s.
 146 */
 147static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
 148{
 149        slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
 150        slobidx_t offset = next - base;
 151
 152        if (size > 1) {
 153                s[0].units = size;
 154                s[1].units = offset;
 155        } else
 156                s[0].units = -offset;
 157}
 158
 159/*
 160 * Return the size of a slob block.
 161 */
 162static slobidx_t slob_units(slob_t *s)
 163{
 164        if (s->units > 0)
 165                return s->units;
 166        return 1;
 167}
 168
 169/*
 170 * Return the next free slob block pointer after this one.
 171 */
 172static slob_t *slob_next(slob_t *s)
 173{
 174        slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
 175        slobidx_t next;
 176
 177        if (s[0].units < 0)
 178                next = -s[0].units;
 179        else
 180                next = s[1].units;
 181        return base+next;
 182}
 183
 184/*
 185 * Returns true if s is the last free block in its page.
 186 */
 187static int slob_last(slob_t *s)
 188{
 189        return !((unsigned long)slob_next(s) & ~PAGE_MASK);
 190}
 191
 192static void *slob_new_pages(gfp_t gfp, int order, int node)
 193{
 194        void *page;
 195
 196#ifdef CONFIG_NUMA
 197        if (node != -1)
 198                page = alloc_pages_exact_node(node, gfp, order);
 199        else
 200#endif
 201                page = alloc_pages(gfp, order);
 202
 203        if (!page)
 204                return NULL;
 205
 206        return page_address(page);
 207}
 208
 209static void slob_free_pages(void *b, int order)
 210{
 211        if (current->reclaim_state)
 212                current->reclaim_state->reclaimed_slab += 1 << order;
 213        free_pages((unsigned long)b, order);
 214}
 215
 216/*
 217 * Allocate a slob block within a given slob_page sp.
 218 */
 219static void *slob_page_alloc(struct page *sp, size_t size, int align)
 220{
 221        slob_t *prev, *cur, *aligned = NULL;
 222        int delta = 0, units = SLOB_UNITS(size);
 223
 224        for (prev = NULL, cur = sp->freelist; ; prev = cur, cur = slob_next(cur)) {
 225                slobidx_t avail = slob_units(cur);
 226
 227                if (align) {
 228                        aligned = (slob_t *)ALIGN((unsigned long)cur, align);
 229                        delta = aligned - cur;
 230                }
 231                if (avail >= units + delta) { /* room enough? */
 232                        slob_t *next;
 233
 234                        if (delta) { /* need to fragment head to align? */
 235                                next = slob_next(cur);
 236                                set_slob(aligned, avail - delta, next);
 237                                set_slob(cur, delta, aligned);
 238                                prev = cur;
 239                                cur = aligned;
 240                                avail = slob_units(cur);
 241                        }
 242
 243                        next = slob_next(cur);
 244                        if (avail == units) { /* exact fit? unlink. */
 245                                if (prev)
 246                                        set_slob(prev, slob_units(prev), next);
 247                                else
 248                                        sp->freelist = next;
 249                        } else { /* fragment */
 250                                if (prev)
 251                                        set_slob(prev, slob_units(prev), cur + units);
 252                                else
 253                                        sp->freelist = cur + units;
 254                                set_slob(cur + units, avail - units, next);
 255                        }
 256
 257                        sp->units -= units;
 258                        if (!sp->units)
 259                                clear_slob_page_free(sp);
 260                        return cur;
 261                }
 262                if (slob_last(cur))
 263                        return NULL;
 264        }
 265}
 266
 267/*
 268 * slob_alloc: entry point into the slob allocator.
 269 */
 270static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
 271{
 272        struct page *sp;
 273        struct list_head *prev;
 274        struct list_head *slob_list;
 275        slob_t *b = NULL;
 276        unsigned long flags;
 277
 278        if (size < SLOB_BREAK1)
 279                slob_list = &free_slob_small;
 280        else if (size < SLOB_BREAK2)
 281                slob_list = &free_slob_medium;
 282        else
 283                slob_list = &free_slob_large;
 284
 285        spin_lock_irqsave(&slob_lock, flags);
 286        /* Iterate through each partially free page, try to find room */
 287        list_for_each_entry(sp, slob_list, list) {
 288#ifdef CONFIG_NUMA
 289                /*
 290                 * If there's a node specification, search for a partial
 291                 * page with a matching node id in the freelist.
 292                 */
 293                if (node != -1 && page_to_nid(sp) != node)
 294                        continue;
 295#endif
 296                /* Enough room on this page? */
 297                if (sp->units < SLOB_UNITS(size))
 298                        continue;
 299
 300                /* Attempt to alloc */
 301                prev = sp->list.prev;
 302                b = slob_page_alloc(sp, size, align);
 303                if (!b)
 304                        continue;
 305
 306                /* Improve fragment distribution and reduce our average
 307                 * search time by starting our next search here. (see
 308                 * Knuth vol 1, sec 2.5, pg 449) */
 309                if (prev != slob_list->prev &&
 310                                slob_list->next != prev->next)
 311                        list_move_tail(slob_list, prev->next);
 312                break;
 313        }
 314        spin_unlock_irqrestore(&slob_lock, flags);
 315
 316        /* Not enough space: must allocate a new page */
 317        if (!b) {
 318                b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
 319                if (!b)
 320                        return NULL;
 321                sp = virt_to_page(b);
 322                __SetPageSlab(sp);
 323
 324                spin_lock_irqsave(&slob_lock, flags);
 325                sp->units = SLOB_UNITS(PAGE_SIZE);
 326                sp->freelist = b;
 327                INIT_LIST_HEAD(&sp->list);
 328                set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
 329                set_slob_page_free(sp, slob_list);
 330                b = slob_page_alloc(sp, size, align);
 331                BUG_ON(!b);
 332                spin_unlock_irqrestore(&slob_lock, flags);
 333        }
 334        if (unlikely((gfp & __GFP_ZERO) && b))
 335                memset(b, 0, size);
 336        return b;
 337}
 338
 339/*
 340 * slob_free: entry point into the slob allocator.
 341 */
 342static void slob_free(void *block, int size)
 343{
 344        struct page *sp;
 345        slob_t *prev, *next, *b = (slob_t *)block;
 346        slobidx_t units;
 347        unsigned long flags;
 348        struct list_head *slob_list;
 349
 350        if (unlikely(ZERO_OR_NULL_PTR(block)))
 351                return;
 352        BUG_ON(!size);
 353
 354        sp = virt_to_page(block);
 355        units = SLOB_UNITS(size);
 356
 357        spin_lock_irqsave(&slob_lock, flags);
 358
 359        if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
 360                /* Go directly to page allocator. Do not pass slob allocator */
 361                if (slob_page_free(sp))
 362                        clear_slob_page_free(sp);
 363                spin_unlock_irqrestore(&slob_lock, flags);
 364                __ClearPageSlab(sp);
 365                reset_page_mapcount(sp);
 366                slob_free_pages(b, 0);
 367                return;
 368        }
 369
 370        if (!slob_page_free(sp)) {
 371                /* This slob page is about to become partially free. Easy! */
 372                sp->units = units;
 373                sp->freelist = b;
 374                set_slob(b, units,
 375                        (void *)((unsigned long)(b +
 376                                        SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
 377                if (size < SLOB_BREAK1)
 378                        slob_list = &free_slob_small;
 379                else if (size < SLOB_BREAK2)
 380                        slob_list = &free_slob_medium;
 381                else
 382                        slob_list = &free_slob_large;
 383                set_slob_page_free(sp, slob_list);
 384                goto out;
 385        }
 386
 387        /*
 388         * Otherwise the page is already partially free, so find reinsertion
 389         * point.
 390         */
 391        sp->units += units;
 392
 393        if (b < (slob_t *)sp->freelist) {
 394                if (b + units == sp->freelist) {
 395                        units += slob_units(sp->freelist);
 396                        sp->freelist = slob_next(sp->freelist);
 397                }
 398                set_slob(b, units, sp->freelist);
 399                sp->freelist = b;
 400        } else {
 401                prev = sp->freelist;
 402                next = slob_next(prev);
 403                while (b > next) {
 404                        prev = next;
 405                        next = slob_next(prev);
 406                }
 407
 408                if (!slob_last(prev) && b + units == next) {
 409                        units += slob_units(next);
 410                        set_slob(b, units, slob_next(next));
 411                } else
 412                        set_slob(b, units, next);
 413
 414                if (prev + slob_units(prev) == b) {
 415                        units = slob_units(b) + slob_units(prev);
 416                        set_slob(prev, units, slob_next(b));
 417                } else
 418                        set_slob(prev, slob_units(prev), b);
 419        }
 420out:
 421        spin_unlock_irqrestore(&slob_lock, flags);
 422}
 423
 424/*
 425 * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
 426 */
 427
 428void *__kmalloc_node(size_t size, gfp_t gfp, int node)
 429{
 430        unsigned int *m;
 431        int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 432        void *ret;
 433
 434        gfp &= gfp_allowed_mask;
 435
 436        lockdep_trace_alloc(gfp);
 437
 438        if (size < PAGE_SIZE - align) {
 439                if (!size)
 440                        return ZERO_SIZE_PTR;
 441
 442                m = slob_alloc(size + align, gfp, align, node);
 443
 444                if (!m)
 445                        return NULL;
 446                *m = size;
 447                ret = (void *)m + align;
 448
 449                trace_kmalloc_node(_RET_IP_, ret,
 450                                   size, size + align, gfp, node);
 451        } else {
 452                unsigned int order = get_order(size);
 453
 454                if (likely(order))
 455                        gfp |= __GFP_COMP;
 456                ret = slob_new_pages(gfp, order, node);
 457                if (ret) {
 458                        struct page *page;
 459                        page = virt_to_page(ret);
 460                        page->private = size;
 461                }
 462
 463                trace_kmalloc_node(_RET_IP_, ret,
 464                                   size, PAGE_SIZE << order, gfp, node);
 465        }
 466
 467        kmemleak_alloc(ret, size, 1, gfp);
 468        return ret;
 469}
 470EXPORT_SYMBOL(__kmalloc_node);
 471
 472void kfree(const void *block)
 473{
 474        struct page *sp;
 475
 476        trace_kfree(_RET_IP_, block);
 477
 478        if (unlikely(ZERO_OR_NULL_PTR(block)))
 479                return;
 480        kmemleak_free(block);
 481
 482        sp = virt_to_page(block);
 483        if (PageSlab(sp)) {
 484                int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 485                unsigned int *m = (unsigned int *)(block - align);
 486                slob_free(m, *m + align);
 487        } else
 488                put_page(sp);
 489}
 490EXPORT_SYMBOL(kfree);
 491
 492/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
 493size_t ksize(const void *block)
 494{
 495        struct page *sp;
 496
 497        BUG_ON(!block);
 498        if (unlikely(block == ZERO_SIZE_PTR))
 499                return 0;
 500
 501        sp = virt_to_page(block);
 502        if (PageSlab(sp)) {
 503                int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 504                unsigned int *m = (unsigned int *)(block - align);
 505                return SLOB_UNITS(*m) * SLOB_UNIT;
 506        } else
 507                return sp->private;
 508}
 509EXPORT_SYMBOL(ksize);
 510
 511struct kmem_cache *__kmem_cache_create(const char *name, size_t size,
 512        size_t align, unsigned long flags, void (*ctor)(void *))
 513{
 514        struct kmem_cache *c;
 515
 516        c = slob_alloc(sizeof(struct kmem_cache),
 517                GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
 518
 519        if (c) {
 520                c->name = name;
 521                c->size = size;
 522                if (flags & SLAB_DESTROY_BY_RCU) {
 523                        /* leave room for rcu footer at the end of object */
 524                        c->size += sizeof(struct slob_rcu);
 525                }
 526                c->flags = flags;
 527                c->ctor = ctor;
 528                /* ignore alignment unless it's forced */
 529                c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 530                if (c->align < ARCH_SLAB_MINALIGN)
 531                        c->align = ARCH_SLAB_MINALIGN;
 532                if (c->align < align)
 533                        c->align = align;
 534
 535                kmemleak_alloc(c, sizeof(struct kmem_cache), 1, GFP_KERNEL);
 536                c->refcount = 1;
 537        }
 538        return c;
 539}
 540
 541void kmem_cache_destroy(struct kmem_cache *c)
 542{
 543        kmemleak_free(c);
 544        if (c->flags & SLAB_DESTROY_BY_RCU)
 545                rcu_barrier();
 546        slob_free(c, sizeof(struct kmem_cache));
 547}
 548EXPORT_SYMBOL(kmem_cache_destroy);
 549
 550void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
 551{
 552        void *b;
 553
 554        flags &= gfp_allowed_mask;
 555
 556        lockdep_trace_alloc(flags);
 557
 558        if (c->size < PAGE_SIZE) {
 559                b = slob_alloc(c->size, flags, c->align, node);
 560                trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
 561                                            SLOB_UNITS(c->size) * SLOB_UNIT,
 562                                            flags, node);
 563        } else {
 564                b = slob_new_pages(flags, get_order(c->size), node);
 565                trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
 566                                            PAGE_SIZE << get_order(c->size),
 567                                            flags, node);
 568        }
 569
 570        if (c->ctor)
 571                c->ctor(b);
 572
 573        kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
 574        return b;
 575}
 576EXPORT_SYMBOL(kmem_cache_alloc_node);
 577
 578static void __kmem_cache_free(void *b, int size)
 579{
 580        if (size < PAGE_SIZE)
 581                slob_free(b, size);
 582        else
 583                slob_free_pages(b, get_order(size));
 584}
 585
 586static void kmem_rcu_free(struct rcu_head *head)
 587{
 588        struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
 589        void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
 590
 591        __kmem_cache_free(b, slob_rcu->size);
 592}
 593
 594void kmem_cache_free(struct kmem_cache *c, void *b)
 595{
 596        kmemleak_free_recursive(b, c->flags);
 597        if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
 598                struct slob_rcu *slob_rcu;
 599                slob_rcu = b + (c->size - sizeof(struct slob_rcu));
 600                slob_rcu->size = c->size;
 601                call_rcu(&slob_rcu->head, kmem_rcu_free);
 602        } else {
 603                __kmem_cache_free(b, c->size);
 604        }
 605
 606        trace_kmem_cache_free(_RET_IP_, b);
 607}
 608EXPORT_SYMBOL(kmem_cache_free);
 609
 610unsigned int kmem_cache_size(struct kmem_cache *c)
 611{
 612        return c->size;
 613}
 614EXPORT_SYMBOL(kmem_cache_size);
 615
 616int kmem_cache_shrink(struct kmem_cache *d)
 617{
 618        return 0;
 619}
 620EXPORT_SYMBOL(kmem_cache_shrink);
 621
 622void __init kmem_cache_init(void)
 623{
 624        slab_state = UP;
 625}
 626
 627void __init kmem_cache_init_late(void)
 628{
 629        slab_state = FULL;
 630}
 631
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