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 <linux/mm.h>
  63#include <linux/swap.h> /* struct reclaim_state */
  64#include <linux/cache.h>
  65#include <linux/init.h>
  66#include <linux/module.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/*
  76 * slob_block has a field 'units', which indicates size of block if +ve,
  77 * or offset of next block if -ve (in SLOB_UNITs).
  78 *
  79 * Free blocks of size 1 unit simply contain the offset of the next block.
  80 * Those with larger size contain their size in the first SLOB_UNIT of
  81 * memory, and the offset of the next free block in the second SLOB_UNIT.
  82 */
  83#if PAGE_SIZE <= (32767 * 2)
  84typedef s16 slobidx_t;
  85#else
  86typedef s32 slobidx_t;
  87#endif
  88
  89struct slob_block {
  90        slobidx_t units;
  91};
  92typedef struct slob_block slob_t;
  93
  94/*
  95 * We use struct page fields to manage some slob allocation aspects,
  96 * however to avoid the horrible mess in include/linux/mm_types.h, we'll
  97 * just define our own struct page type variant here.
  98 */
  99struct slob_page {
 100        union {
 101                struct {
 102                        unsigned long flags;    /* mandatory */
 103                        atomic_t _count;        /* mandatory */
 104                        slobidx_t units;        /* free units left in page */
 105                        unsigned long pad[2];
 106                        slob_t *free;           /* first free slob_t in page */
 107                        struct list_head list;  /* linked list of free pages */
 108                };
 109                struct page page;
 110        };
 111};
 112static inline void struct_slob_page_wrong_size(void)
 113{ BUILD_BUG_ON(sizeof(struct slob_page) != sizeof(struct page)); }
 114
 115/*
 116 * free_slob_page: call before a slob_page is returned to the page allocator.
 117 */
 118static inline void free_slob_page(struct slob_page *sp)
 119{
 120        reset_page_mapcount(&sp->page);
 121        sp->page.mapping = NULL;
 122}
 123
 124/*
 125 * All partially free slob pages go on these lists.
 126 */
 127#define SLOB_BREAK1 256
 128#define SLOB_BREAK2 1024
 129static LIST_HEAD(free_slob_small);
 130static LIST_HEAD(free_slob_medium);
 131static LIST_HEAD(free_slob_large);
 132
 133/*
 134 * is_slob_page: True for all slob pages (false for bigblock pages)
 135 */
 136static inline int is_slob_page(struct slob_page *sp)
 137{
 138        return PageSlab((struct page *)sp);
 139}
 140
 141static inline void set_slob_page(struct slob_page *sp)
 142{
 143        __SetPageSlab((struct page *)sp);
 144}
 145
 146static inline void clear_slob_page(struct slob_page *sp)
 147{
 148        __ClearPageSlab((struct page *)sp);
 149}
 150
 151static inline struct slob_page *slob_page(const void *addr)
 152{
 153        return (struct slob_page *)virt_to_page(addr);
 154}
 155
 156/*
 157 * slob_page_free: true for pages on free_slob_pages list.
 158 */
 159static inline int slob_page_free(struct slob_page *sp)
 160{
 161        return PageSlobFree((struct page *)sp);
 162}
 163
 164static void set_slob_page_free(struct slob_page *sp, struct list_head *list)
 165{
 166        list_add(&sp->list, list);
 167        __SetPageSlobFree((struct page *)sp);
 168}
 169
 170static inline void clear_slob_page_free(struct slob_page *sp)
 171{
 172        list_del(&sp->list);
 173        __ClearPageSlobFree((struct page *)sp);
 174}
 175
 176#define SLOB_UNIT sizeof(slob_t)
 177#define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
 178#define SLOB_ALIGN L1_CACHE_BYTES
 179
 180/*
 181 * struct slob_rcu is inserted at the tail of allocated slob blocks, which
 182 * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
 183 * the block using call_rcu.
 184 */
 185struct slob_rcu {
 186        struct rcu_head head;
 187        int size;
 188};
 189
 190/*
 191 * slob_lock protects all slob allocator structures.
 192 */
 193static DEFINE_SPINLOCK(slob_lock);
 194
 195/*
 196 * Encode the given size and next info into a free slob block s.
 197 */
 198static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
 199{
 200        slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
 201        slobidx_t offset = next - base;
 202
 203        if (size > 1) {
 204                s[0].units = size;
 205                s[1].units = offset;
 206        } else
 207                s[0].units = -offset;
 208}
 209
 210/*
 211 * Return the size of a slob block.
 212 */
 213static slobidx_t slob_units(slob_t *s)
 214{
 215        if (s->units > 0)
 216                return s->units;
 217        return 1;
 218}
 219
 220/*
 221 * Return the next free slob block pointer after this one.
 222 */
 223static slob_t *slob_next(slob_t *s)
 224{
 225        slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
 226        slobidx_t next;
 227
 228        if (s[0].units < 0)
 229                next = -s[0].units;
 230        else
 231                next = s[1].units;
 232        return base+next;
 233}
 234
 235/*
 236 * Returns true if s is the last free block in its page.
 237 */
 238static int slob_last(slob_t *s)
 239{
 240        return !((unsigned long)slob_next(s) & ~PAGE_MASK);
 241}
 242
 243static void *slob_new_pages(gfp_t gfp, int order, int node)
 244{
 245        void *page;
 246
 247#ifdef CONFIG_NUMA
 248        if (node != -1)
 249                page = alloc_pages_exact_node(node, gfp, order);
 250        else
 251#endif
 252                page = alloc_pages(gfp, order);
 253
 254        if (!page)
 255                return NULL;
 256
 257        return page_address(page);
 258}
 259
 260static void slob_free_pages(void *b, int order)
 261{
 262        if (current->reclaim_state)
 263                current->reclaim_state->reclaimed_slab += 1 << order;
 264        free_pages((unsigned long)b, order);
 265}
 266
 267/*
 268 * Allocate a slob block within a given slob_page sp.
 269 */
 270static void *slob_page_alloc(struct slob_page *sp, size_t size, int align)
 271{
 272        slob_t *prev, *cur, *aligned = NULL;
 273        int delta = 0, units = SLOB_UNITS(size);
 274
 275        for (prev = NULL, cur = sp->free; ; prev = cur, cur = slob_next(cur)) {
 276                slobidx_t avail = slob_units(cur);
 277
 278                if (align) {
 279                        aligned = (slob_t *)ALIGN((unsigned long)cur, align);
 280                        delta = aligned - cur;
 281                }
 282                if (avail >= units + delta) { /* room enough? */
 283                        slob_t *next;
 284
 285                        if (delta) { /* need to fragment head to align? */
 286                                next = slob_next(cur);
 287                                set_slob(aligned, avail - delta, next);
 288                                set_slob(cur, delta, aligned);
 289                                prev = cur;
 290                                cur = aligned;
 291                                avail = slob_units(cur);
 292                        }
 293
 294                        next = slob_next(cur);
 295                        if (avail == units) { /* exact fit? unlink. */
 296                                if (prev)
 297                                        set_slob(prev, slob_units(prev), next);
 298                                else
 299                                        sp->free = next;
 300                        } else { /* fragment */
 301                                if (prev)
 302                                        set_slob(prev, slob_units(prev), cur + units);
 303                                else
 304                                        sp->free = cur + units;
 305                                set_slob(cur + units, avail - units, next);
 306                        }
 307
 308                        sp->units -= units;
 309                        if (!sp->units)
 310                                clear_slob_page_free(sp);
 311                        return cur;
 312                }
 313                if (slob_last(cur))
 314                        return NULL;
 315        }
 316}
 317
 318/*
 319 * slob_alloc: entry point into the slob allocator.
 320 */
 321static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
 322{
 323        struct slob_page *sp;
 324        struct list_head *prev;
 325        struct list_head *slob_list;
 326        slob_t *b = NULL;
 327        unsigned long flags;
 328
 329        if (size < SLOB_BREAK1)
 330                slob_list = &free_slob_small;
 331        else if (size < SLOB_BREAK2)
 332                slob_list = &free_slob_medium;
 333        else
 334                slob_list = &free_slob_large;
 335
 336        spin_lock_irqsave(&slob_lock, flags);
 337        /* Iterate through each partially free page, try to find room */
 338        list_for_each_entry(sp, slob_list, list) {
 339#ifdef CONFIG_NUMA
 340                /*
 341                 * If there's a node specification, search for a partial
 342                 * page with a matching node id in the freelist.
 343                 */
 344                if (node != -1 && page_to_nid(&sp->page) != node)
 345                        continue;
 346#endif
 347                /* Enough room on this page? */
 348                if (sp->units < SLOB_UNITS(size))
 349                        continue;
 350
 351                /* Attempt to alloc */
 352                prev = sp->list.prev;
 353                b = slob_page_alloc(sp, size, align);
 354                if (!b)
 355                        continue;
 356
 357                /* Improve fragment distribution and reduce our average
 358                 * search time by starting our next search here. (see
 359                 * Knuth vol 1, sec 2.5, pg 449) */
 360                if (prev != slob_list->prev &&
 361                                slob_list->next != prev->next)
 362                        list_move_tail(slob_list, prev->next);
 363                break;
 364        }
 365        spin_unlock_irqrestore(&slob_lock, flags);
 366
 367        /* Not enough space: must allocate a new page */
 368        if (!b) {
 369                b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
 370                if (!b)
 371                        return NULL;
 372                sp = slob_page(b);
 373                set_slob_page(sp);
 374
 375                spin_lock_irqsave(&slob_lock, flags);
 376                sp->units = SLOB_UNITS(PAGE_SIZE);
 377                sp->free = b;
 378                INIT_LIST_HEAD(&sp->list);
 379                set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
 380                set_slob_page_free(sp, slob_list);
 381                b = slob_page_alloc(sp, size, align);
 382                BUG_ON(!b);
 383                spin_unlock_irqrestore(&slob_lock, flags);
 384        }
 385        if (unlikely((gfp & __GFP_ZERO) && b))
 386                memset(b, 0, size);
 387        return b;
 388}
 389
 390/*
 391 * slob_free: entry point into the slob allocator.
 392 */
 393static void slob_free(void *block, int size)
 394{
 395        struct slob_page *sp;
 396        slob_t *prev, *next, *b = (slob_t *)block;
 397        slobidx_t units;
 398        unsigned long flags;
 399        struct list_head *slob_list;
 400
 401        if (unlikely(ZERO_OR_NULL_PTR(block)))
 402                return;
 403        BUG_ON(!size);
 404
 405        sp = slob_page(block);
 406        units = SLOB_UNITS(size);
 407
 408        spin_lock_irqsave(&slob_lock, flags);
 409
 410        if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
 411                /* Go directly to page allocator. Do not pass slob allocator */
 412                if (slob_page_free(sp))
 413                        clear_slob_page_free(sp);
 414                spin_unlock_irqrestore(&slob_lock, flags);
 415                clear_slob_page(sp);
 416                free_slob_page(sp);
 417                slob_free_pages(b, 0);
 418                return;
 419        }
 420
 421        if (!slob_page_free(sp)) {
 422                /* This slob page is about to become partially free. Easy! */
 423                sp->units = units;
 424                sp->free = b;
 425                set_slob(b, units,
 426                        (void *)((unsigned long)(b +
 427                                        SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
 428                if (size < SLOB_BREAK1)
 429                        slob_list = &free_slob_small;
 430                else if (size < SLOB_BREAK2)
 431                        slob_list = &free_slob_medium;
 432                else
 433                        slob_list = &free_slob_large;
 434                set_slob_page_free(sp, slob_list);
 435                goto out;
 436        }
 437
 438        /*
 439         * Otherwise the page is already partially free, so find reinsertion
 440         * point.
 441         */
 442        sp->units += units;
 443
 444        if (b < sp->free) {
 445                if (b + units == sp->free) {
 446                        units += slob_units(sp->free);
 447                        sp->free = slob_next(sp->free);
 448                }
 449                set_slob(b, units, sp->free);
 450                sp->free = b;
 451        } else {
 452                prev = sp->free;
 453                next = slob_next(prev);
 454                while (b > next) {
 455                        prev = next;
 456                        next = slob_next(prev);
 457                }
 458
 459                if (!slob_last(prev) && b + units == next) {
 460                        units += slob_units(next);
 461                        set_slob(b, units, slob_next(next));
 462                } else
 463                        set_slob(b, units, next);
 464
 465                if (prev + slob_units(prev) == b) {
 466                        units = slob_units(b) + slob_units(prev);
 467                        set_slob(prev, units, slob_next(b));
 468                } else
 469                        set_slob(prev, slob_units(prev), b);
 470        }
 471out:
 472        spin_unlock_irqrestore(&slob_lock, flags);
 473}
 474
 475/*
 476 * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
 477 */
 478
 479void *__kmalloc_node(size_t size, gfp_t gfp, int node)
 480{
 481        unsigned int *m;
 482        int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 483        void *ret;
 484
 485        gfp &= gfp_allowed_mask;
 486
 487        lockdep_trace_alloc(gfp);
 488
 489        if (size < PAGE_SIZE - align) {
 490                if (!size)
 491                        return ZERO_SIZE_PTR;
 492
 493                m = slob_alloc(size + align, gfp, align, node);
 494
 495                if (!m)
 496                        return NULL;
 497                *m = size;
 498                ret = (void *)m + align;
 499
 500                trace_kmalloc_node(_RET_IP_, ret,
 501                                   size, size + align, gfp, node);
 502        } else {
 503                unsigned int order = get_order(size);
 504
 505                if (likely(order))
 506                        gfp |= __GFP_COMP;
 507                ret = slob_new_pages(gfp, order, node);
 508                if (ret) {
 509                        struct page *page;
 510                        page = virt_to_page(ret);
 511                        page->private = size;
 512                }
 513
 514                trace_kmalloc_node(_RET_IP_, ret,
 515                                   size, PAGE_SIZE << order, gfp, node);
 516        }
 517
 518        kmemleak_alloc(ret, size, 1, gfp);
 519        return ret;
 520}
 521EXPORT_SYMBOL(__kmalloc_node);
 522
 523void kfree(const void *block)
 524{
 525        struct slob_page *sp;
 526
 527        trace_kfree(_RET_IP_, block);
 528
 529        if (unlikely(ZERO_OR_NULL_PTR(block)))
 530                return;
 531        kmemleak_free(block);
 532
 533        sp = slob_page(block);
 534        if (is_slob_page(sp)) {
 535                int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 536                unsigned int *m = (unsigned int *)(block - align);
 537                slob_free(m, *m + align);
 538        } else
 539                put_page(&sp->page);
 540}
 541EXPORT_SYMBOL(kfree);
 542
 543/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
 544size_t ksize(const void *block)
 545{
 546        struct slob_page *sp;
 547
 548        BUG_ON(!block);
 549        if (unlikely(block == ZERO_SIZE_PTR))
 550                return 0;
 551
 552        sp = slob_page(block);
 553        if (is_slob_page(sp)) {
 554                int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 555                unsigned int *m = (unsigned int *)(block - align);
 556                return SLOB_UNITS(*m) * SLOB_UNIT;
 557        } else
 558                return sp->page.private;
 559}
 560EXPORT_SYMBOL(ksize);
 561
 562struct kmem_cache {
 563        unsigned int size, align;
 564        unsigned long flags;
 565        const char *name;
 566        void (*ctor)(void *);
 567};
 568
 569struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 570        size_t align, unsigned long flags, void (*ctor)(void *))
 571{
 572        struct kmem_cache *c;
 573
 574        c = slob_alloc(sizeof(struct kmem_cache),
 575                GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
 576
 577        if (c) {
 578                c->name = name;
 579                c->size = size;
 580                if (flags & SLAB_DESTROY_BY_RCU) {
 581                        /* leave room for rcu footer at the end of object */
 582                        c->size += sizeof(struct slob_rcu);
 583                }
 584                c->flags = flags;
 585                c->ctor = ctor;
 586                /* ignore alignment unless it's forced */
 587                c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 588                if (c->align < ARCH_SLAB_MINALIGN)
 589                        c->align = ARCH_SLAB_MINALIGN;
 590                if (c->align < align)
 591                        c->align = align;
 592        } else if (flags & SLAB_PANIC)
 593                panic("Cannot create slab cache %s\n", name);
 594
 595        kmemleak_alloc(c, sizeof(struct kmem_cache), 1, GFP_KERNEL);
 596        return c;
 597}
 598EXPORT_SYMBOL(kmem_cache_create);
 599
 600void kmem_cache_destroy(struct kmem_cache *c)
 601{
 602        kmemleak_free(c);
 603        if (c->flags & SLAB_DESTROY_BY_RCU)
 604                rcu_barrier();
 605        slob_free(c, sizeof(struct kmem_cache));
 606}
 607EXPORT_SYMBOL(kmem_cache_destroy);
 608
 609void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
 610{
 611        void *b;
 612
 613        flags &= gfp_allowed_mask;
 614
 615        lockdep_trace_alloc(flags);
 616
 617        if (c->size < PAGE_SIZE) {
 618                b = slob_alloc(c->size, flags, c->align, node);
 619                trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
 620                                            SLOB_UNITS(c->size) * SLOB_UNIT,
 621                                            flags, node);
 622        } else {
 623                b = slob_new_pages(flags, get_order(c->size), node);
 624                trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
 625                                            PAGE_SIZE << get_order(c->size),
 626                                            flags, node);
 627        }
 628
 629        if (c->ctor)
 630                c->ctor(b);
 631
 632        kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
 633        return b;
 634}
 635EXPORT_SYMBOL(kmem_cache_alloc_node);
 636
 637static void __kmem_cache_free(void *b, int size)
 638{
 639        if (size < PAGE_SIZE)
 640                slob_free(b, size);
 641        else
 642                slob_free_pages(b, get_order(size));
 643}
 644
 645static void kmem_rcu_free(struct rcu_head *head)
 646{
 647        struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
 648        void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
 649
 650        __kmem_cache_free(b, slob_rcu->size);
 651}
 652
 653void kmem_cache_free(struct kmem_cache *c, void *b)
 654{
 655        kmemleak_free_recursive(b, c->flags);
 656        if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
 657                struct slob_rcu *slob_rcu;
 658                slob_rcu = b + (c->size - sizeof(struct slob_rcu));
 659                slob_rcu->size = c->size;
 660                call_rcu(&slob_rcu->head, kmem_rcu_free);
 661        } else {
 662                __kmem_cache_free(b, c->size);
 663        }
 664
 665        trace_kmem_cache_free(_RET_IP_, b);
 666}
 667EXPORT_SYMBOL(kmem_cache_free);
 668
 669unsigned int kmem_cache_size(struct kmem_cache *c)
 670{
 671        return c->size;
 672}
 673EXPORT_SYMBOL(kmem_cache_size);
 674
 675int kmem_cache_shrink(struct kmem_cache *d)
 676{
 677        return 0;
 678}
 679EXPORT_SYMBOL(kmem_cache_shrink);
 680
 681static unsigned int slob_ready __read_mostly;
 682
 683int slab_is_available(void)
 684{
 685        return slob_ready;
 686}
 687
 688void __init kmem_cache_init(void)
 689{
 690        slob_ready = 1;
 691}
 692
 693void __init kmem_cache_init_late(void)
 694{
 695        /* Nothing to do */
 696}
 697
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