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