mm/slob.c

   1 /*
   2  * SLOB Allocator: Simple List Of Blocks
   3  *
   4  * Matt Mackall <mpm@selenic.com> 12/30/03
   5  *
   6  * How SLOB works:
   7  *
   8  * The core of SLOB is a traditional K&R style heap allocator, with
   9  * support for returning aligned objects. The granularity of this
  10  * allocator is 8 bytes on x86, though it's perhaps possible to reduce
  11  * this to 4 if it's deemed worth the effort. The slob heap is a
  12  * singly-linked list of pages from __get_free_page, grown on demand
  13  * and allocation from the heap is currently first-fit.
  14  *
  15  * Above this is an implementation of kmalloc/kfree. Blocks returned
  16  * from kmalloc are 8-byte aligned and prepended with a 8-byte header.
  17  * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
  18  * __get_free_pages directly so that it can return page-aligned blocks
  19  * and keeps a linked list of such pages and their orders. These
  20  * objects are detected in kfree() by their page alignment.
  21  *
  22  * SLAB is emulated on top of SLOB by simply calling constructors and
  23  * destructors for every SLAB allocation. Objects are returned with
  24  * the 8-byte alignment unless the SLAB_MUST_HWCACHE_ALIGN flag is
  25  * set, in which case the low-level allocator will fragment blocks to
  26  * create the proper alignment. Again, objects of page-size or greater
  27  * are allocated by calling __get_free_pages. As SLAB objects know
  28  * their size, no separate size bookkeeping is necessary and there is
  29  * essentially no allocation space overhead.
  30  */
  31
  32 #include <linux/slab.h>
  33 #include <linux/mm.h>
  34 #include <linux/cache.h>
  35 #include <linux/init.h>
  36 #include <linux/module.h>
  37 #include <linux/timer.h>
  38
  39 struct slob_block {
  40         int units;
  41         struct slob_block *next;
  42 };
  43 typedef struct slob_block slob_t;
  44
  45 #define SLOB_UNIT sizeof(slob_t)
  46 #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
  47 #define SLOB_ALIGN L1_CACHE_BYTES
  48
  49 struct bigblock {
  50         int order;
  51         void *pages;
  52         struct bigblock *next;
  53 };
  54 typedef struct bigblock bigblock_t;
  55
  56 static slob_t arena = { .next = &arena, .units = 1 };
  57 static slob_t *slobfree = &arena;
  58 static bigblock_t *bigblocks;
  59 static DEFINE_SPINLOCK(slob_lock);
  60 static DEFINE_SPINLOCK(block_lock);
  61
  62 static void slob_free(void *b, int size);
  63 static void slob_timer_cbk(void);
  64
  65
  66 static void *slob_alloc(size_t size, gfp_t gfp, int align)
  67 {
  68         slob_t *prev, *cur, *aligned = 0;
  69         int delta = 0, units = SLOB_UNITS(size);
  70         unsigned long flags;
  71
  72         spin_lock_irqsave(&slob_lock, flags);
  73         prev = slobfree;
  74         for (cur = prev->next; ; prev = cur, cur = cur->next) {
  75                 if (align) {
  76                         aligned = (slob_t *)ALIGN((unsigned long)cur, align);
  77                         delta = aligned - cur;
  78                 }
  79                 if (cur->units >= units + delta) { /* room enough? */
  80                         if (delta) { /* need to fragment head to align? */
  81                                 aligned->units = cur->units - delta;
  82                                 aligned->next = cur->next;
  83                                 cur->next = aligned;
  84                                 cur->units = delta;
  85                                 prev = cur;
  86                                 cur = aligned;
  87                         }
  88
  89                         if (cur->units == units) /* exact fit? */
  90                                 prev->next = cur->next; /* unlink */
  91                         else { /* fragment */
  92                                 prev->next = cur + units;
  93                                 prev->next->units = cur->units - units;
  94                                 prev->next->next = cur->next;
  95                                 cur->units = units;
  96                         }
  97
  98                         slobfree = prev;
  99                         spin_unlock_irqrestore(&slob_lock, flags);
 100                         return cur;
 101                 }
 102                 if (cur == slobfree) {
 103                         spin_unlock_irqrestore(&slob_lock, flags);
 104
 105                         if (size == PAGE_SIZE) /* trying to shrink arena? */
 106                                 return 0;
 107
 108                         cur = (slob_t *)__get_free_page(gfp);
 109                         if (!cur)
 110                                 return 0;
 111
 112                         slob_free(cur, PAGE_SIZE);
 113                         spin_lock_irqsave(&slob_lock, flags);
 114                         cur = slobfree;
 115                 }
 116         }
 117 }
 118
 119 static void slob_free(void *block, int size)
 120 {
 121         slob_t *cur, *b = (slob_t *)block;
 122         unsigned long flags;
 123
 124         if (!block)
 125                 return;
 126
 127         if (size)
 128                 b->units = SLOB_UNITS(size);
 129
 130         /* Find reinsertion point */
 131         spin_lock_irqsave(&slob_lock, flags);
 132         for (cur = slobfree; !(b > cur && b < cur->next); cur = cur->next)
 133                 if (cur >= cur->next && (b > cur || b < cur->next))
 134                         break;
 135
 136         if (b + b->units == cur->next) {
 137                 b->units += cur->next->units;
 138                 b->next = cur->next->next;
 139         } else
 140                 b->next = cur->next;
 141
 142         if (cur + cur->units == b) {
 143                 cur->units += b->units;
 144                 cur->next = b->next;
 145         } else
 146                 cur->next = b;
 147
 148         slobfree = cur;
 149
 150         spin_unlock_irqrestore(&slob_lock, flags);
 151 }
 152
 153 static int FASTCALL(find_order(int size));
 154 static int fastcall find_order(int size)
 155 {
 156         int order = 0;
 157         for ( ; size > 4096 ; size >>=1)
 158                 order++;
 159         return order;
 160 }
 161
 162 void *__kmalloc(size_t size, gfp_t gfp)
 163 {
 164         slob_t *m;
 165         bigblock_t *bb;
 166         unsigned long flags;
 167
 168         if (size < PAGE_SIZE - SLOB_UNIT) {
 169                 m = slob_alloc(size + SLOB_UNIT, gfp, 0);
 170                 return m ? (void *)(m + 1) : 0;
 171         }
 172
 173         bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
 174         if (!bb)
 175                 return 0;
 176
 177         bb->order = find_order(size);
 178         bb->pages = (void *)__get_free_pages(gfp, bb->order);
 179
 180         if (bb->pages) {
 181                 spin_lock_irqsave(&block_lock, flags);
 182                 bb->next = bigblocks;
 183                 bigblocks = bb;
 184                 spin_unlock_irqrestore(&block_lock, flags);
 185                 return bb->pages;
 186         }
 187
 188         slob_free(bb, sizeof(bigblock_t));
 189         return 0;
 190 }
 191 EXPORT_SYMBOL(__kmalloc);
 192
 193 /**
 194  * krealloc - reallocate memory. The contents will remain unchanged.
 195  *
 196  * @p: object to reallocate memory for.
 197  * @new_size: how many bytes of memory are required.
 198  * @flags: the type of memory to allocate.
 199  *
 200  * The contents of the object pointed to are preserved up to the
 201  * lesser of the new and old sizes.  If @p is %NULL, krealloc()
 202  * behaves exactly like kmalloc().  If @size is 0 and @p is not a
 203  * %NULL pointer, the object pointed to is freed.
 204  */
 205 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 206 {
 207         void *ret;
 208
 209         if (unlikely(!p))
 210                 return kmalloc_track_caller(new_size, flags);
 211
 212         if (unlikely(!new_size)) {
 213                 kfree(p);
 214                 return NULL;
 215         }
 216
 217         ret = kmalloc_track_caller(new_size, flags);
 218         if (ret) {
 219                 memcpy(ret, p, min(new_size, ksize(p)));
 220                 kfree(p);
 221         }
 222         return ret;
 223 }
 224 EXPORT_SYMBOL(krealloc);
 225
 226 void kfree(const void *block)
 227 {
 228         bigblock_t *bb, **last = &bigblocks;
 229         unsigned long flags;
 230
 231         if (!block)
 232                 return;
 233
 234         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 235                 /* might be on the big block list */
 236                 spin_lock_irqsave(&block_lock, flags);
 237                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 238                         if (bb->pages == block) {
 239                                 *last = bb->next;
 240                                 spin_unlock_irqrestore(&block_lock, flags);
 241                                 free_pages((unsigned long)block, bb->order);
 242                                 slob_free(bb, sizeof(bigblock_t));
 243                                 return;
 244                         }
 245                 }
 246                 spin_unlock_irqrestore(&block_lock, flags);
 247         }
 248
 249         slob_free((slob_t *)block - 1, 0);
 250         return;
 251 }
 252
 253 EXPORT_SYMBOL(kfree);
 254
 255 size_t ksize(const void *block)
 256 {
 257         bigblock_t *bb;
 258         unsigned long flags;
 259
 260         if (!block)
 261                 return 0;
 262
 263         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 264                 spin_lock_irqsave(&block_lock, flags);
 265                 for (bb = bigblocks; bb; bb = bb->next)
 266                         if (bb->pages == block) {
 267                                 spin_unlock_irqrestore(&slob_lock, flags);
 268                                 return PAGE_SIZE << bb->order;
 269                         }
 270                 spin_unlock_irqrestore(&block_lock, flags);
 271         }
 272
 273         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 274 }
 275
 276 struct kmem_cache {
 277         unsigned int size, align;
 278         const char *name;
 279         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 280         void (*dtor)(void *, struct kmem_cache *, unsigned long);
 281 };
 282
 283 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 284         size_t align, unsigned long flags,
 285         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 286         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 287 {
 288         struct kmem_cache *c;
 289
 290         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 291
 292         if (c) {
 293                 c->name = name;
 294                 c->size = size;
 295                 c->ctor = ctor;
 296                 c->dtor = dtor;
 297                 /* ignore alignment unless it's forced */
 298                 c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 299                 if (c->align < align)
 300                         c->align = align;
 301         }
 302
 303         return c;
 304 }
 305 EXPORT_SYMBOL(kmem_cache_create);
 306
 307 void kmem_cache_destroy(struct kmem_cache *c)
 308 {
 309         slob_free(c, sizeof(struct kmem_cache));
 310 }
 311 EXPORT_SYMBOL(kmem_cache_destroy);
 312
 313 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 314 {
 315         void *b;
 316
 317         if (c->size < PAGE_SIZE)
 318                 b = slob_alloc(c->size, flags, c->align);
 319         else
 320                 b = (void *)__get_free_pages(flags, find_order(c->size));
 321
 322         if (c->ctor)
 323                 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
 324
 325         return b;
 326 }
 327 EXPORT_SYMBOL(kmem_cache_alloc);
 328
 329 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 330 {
 331         void *ret = kmem_cache_alloc(c, flags);
 332         if (ret)
 333                 memset(ret, 0, c->size);
 334
 335         return ret;
 336 }
 337 EXPORT_SYMBOL(kmem_cache_zalloc);
 338
 339 void kmem_cache_free(struct kmem_cache *c, void *b)
 340 {
 341         if (c->dtor)
 342                 c->dtor(b, c, 0);
 343
 344         if (c->size < PAGE_SIZE)
 345                 slob_free(b, c->size);
 346         else
 347                 free_pages((unsigned long)b, find_order(c->size));
 348 }
 349 EXPORT_SYMBOL(kmem_cache_free);
 350
 351 unsigned int kmem_cache_size(struct kmem_cache *c)
 352 {
 353         return c->size;
 354 }
 355 EXPORT_SYMBOL(kmem_cache_size);
 356
 357 const char *kmem_cache_name(struct kmem_cache *c)
 358 {
 359         return c->name;
 360 }
 361 EXPORT_SYMBOL(kmem_cache_name);
 362
 363 static struct timer_list slob_timer = TIMER_INITIALIZER(
 364         (void (*)(unsigned long))slob_timer_cbk, 0, 0);
 365
 366 int kmem_cache_shrink(struct kmem_cache *d)
 367 {
 368         return 0;
 369 }
 370 EXPORT_SYMBOL(kmem_cache_shrink);
 371
 372 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
 373 {
 374         return 0;
 375 }
 376
 377 void __init kmem_cache_init(void)
 378 {
 379         slob_timer_cbk();
 380 }
 381
 382 static void slob_timer_cbk(void)
 383 {
 384         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 385
 386         if (p)
 387                 free_page((unsigned long)p);
 388
 389         mod_timer(&slob_timer, jiffies + HZ);
 390 }