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_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 void *__kmalloc(size_t size, gfp_t gfp)
 154 {
 155         slob_t *m;
 156         bigblock_t *bb;
 157         unsigned long flags;
 158
 159         if (size < PAGE_SIZE - SLOB_UNIT) {
 160                 m = slob_alloc(size + SLOB_UNIT, gfp, 0);
 161                 return m ? (void *)(m + 1) : 0;
 162         }
 163
 164         bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
 165         if (!bb)
 166                 return 0;
 167
 168         bb->order = get_order(size);
 169         bb->pages = (void *)__get_free_pages(gfp, bb->order);
 170
 171         if (bb->pages) {
 172                 spin_lock_irqsave(&block_lock, flags);
 173                 bb->next = bigblocks;
 174                 bigblocks = bb;
 175                 spin_unlock_irqrestore(&block_lock, flags);
 176                 return bb->pages;
 177         }
 178
 179         slob_free(bb, sizeof(bigblock_t));
 180         return 0;
 181 }
 182 EXPORT_SYMBOL(__kmalloc);
 183
 184 /**
 185  * krealloc - reallocate memory. The contents will remain unchanged.
 186  *
 187  * @p: object to reallocate memory for.
 188  * @new_size: how many bytes of memory are required.
 189  * @flags: the type of memory to allocate.
 190  *
 191  * The contents of the object pointed to are preserved up to the
 192  * lesser of the new and old sizes.  If @p is %NULL, krealloc()
 193  * behaves exactly like kmalloc().  If @size is 0 and @p is not a
 194  * %NULL pointer, the object pointed to is freed.
 195  */
 196 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 197 {
 198         void *ret;
 199
 200         if (unlikely(!p))
 201                 return kmalloc_track_caller(new_size, flags);
 202
 203         if (unlikely(!new_size)) {
 204                 kfree(p);
 205                 return NULL;
 206         }
 207
 208         ret = kmalloc_track_caller(new_size, flags);
 209         if (ret) {
 210                 memcpy(ret, p, min(new_size, ksize(p)));
 211                 kfree(p);
 212         }
 213         return ret;
 214 }
 215 EXPORT_SYMBOL(krealloc);
 216
 217 void kfree(const void *block)
 218 {
 219         bigblock_t *bb, **last = &bigblocks;
 220         unsigned long flags;
 221
 222         if (!block)
 223                 return;
 224
 225         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 226                 /* might be on the big block list */
 227                 spin_lock_irqsave(&block_lock, flags);
 228                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 229                         if (bb->pages == block) {
 230                                 *last = bb->next;
 231                                 spin_unlock_irqrestore(&block_lock, flags);
 232                                 free_pages((unsigned long)block, bb->order);
 233                                 slob_free(bb, sizeof(bigblock_t));
 234                                 return;
 235                         }
 236                 }
 237                 spin_unlock_irqrestore(&block_lock, flags);
 238         }
 239
 240         slob_free((slob_t *)block - 1, 0);
 241         return;
 242 }
 243
 244 EXPORT_SYMBOL(kfree);
 245
 246 size_t ksize(const void *block)
 247 {
 248         bigblock_t *bb;
 249         unsigned long flags;
 250
 251         if (!block)
 252                 return 0;
 253
 254         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 255                 spin_lock_irqsave(&block_lock, flags);
 256                 for (bb = bigblocks; bb; bb = bb->next)
 257                         if (bb->pages == block) {
 258                                 spin_unlock_irqrestore(&slob_lock, flags);
 259                                 return PAGE_SIZE << bb->order;
 260                         }
 261                 spin_unlock_irqrestore(&block_lock, flags);
 262         }
 263
 264         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 265 }
 266
 267 struct kmem_cache {
 268         unsigned int size, align;
 269         const char *name;
 270         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 271         void (*dtor)(void *, struct kmem_cache *, unsigned long);
 272 };
 273
 274 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 275         size_t align, unsigned long flags,
 276         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 277         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 278 {
 279         struct kmem_cache *c;
 280
 281         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 282
 283         if (c) {
 284                 c->name = name;
 285                 c->size = size;
 286                 c->ctor = ctor;
 287                 c->dtor = dtor;
 288                 /* ignore alignment unless it's forced */
 289                 c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 290                 if (c->align < align)
 291                         c->align = align;
 292         } else if (flags & SLAB_PANIC)
 293                 panic("Cannot create slab cache %s\n", name);
 294
 295         return c;
 296 }
 297 EXPORT_SYMBOL(kmem_cache_create);
 298
 299 void kmem_cache_destroy(struct kmem_cache *c)
 300 {
 301         slob_free(c, sizeof(struct kmem_cache));
 302 }
 303 EXPORT_SYMBOL(kmem_cache_destroy);
 304
 305 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 306 {
 307         void *b;
 308
 309         if (c->size < PAGE_SIZE)
 310                 b = slob_alloc(c->size, flags, c->align);
 311         else
 312                 b = (void *)__get_free_pages(flags, get_order(c->size));
 313
 314         if (c->ctor)
 315                 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
 316
 317         return b;
 318 }
 319 EXPORT_SYMBOL(kmem_cache_alloc);
 320
 321 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 322 {
 323         void *ret = kmem_cache_alloc(c, flags);
 324         if (ret)
 325                 memset(ret, 0, c->size);
 326
 327         return ret;
 328 }
 329 EXPORT_SYMBOL(kmem_cache_zalloc);
 330
 331 void kmem_cache_free(struct kmem_cache *c, void *b)
 332 {
 333         if (c->dtor)
 334                 c->dtor(b, c, 0);
 335
 336         if (c->size < PAGE_SIZE)
 337                 slob_free(b, c->size);
 338         else
 339                 free_pages((unsigned long)b, get_order(c->size));
 340 }
 341 EXPORT_SYMBOL(kmem_cache_free);
 342
 343 unsigned int kmem_cache_size(struct kmem_cache *c)
 344 {
 345         return c->size;
 346 }
 347 EXPORT_SYMBOL(kmem_cache_size);
 348
 349 const char *kmem_cache_name(struct kmem_cache *c)
 350 {
 351         return c->name;
 352 }
 353 EXPORT_SYMBOL(kmem_cache_name);
 354
 355 static struct timer_list slob_timer = TIMER_INITIALIZER(
 356         (void (*)(unsigned long))slob_timer_cbk, 0, 0);
 357
 358 int kmem_cache_shrink(struct kmem_cache *d)
 359 {
 360         return 0;
 361 }
 362 EXPORT_SYMBOL(kmem_cache_shrink);
 363
 364 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
 365 {
 366         return 0;
 367 }
 368
 369 void __init kmem_cache_init(void)
 370 {
 371         slob_timer_cbk();
 372 }
 373
 374 static void slob_timer_cbk(void)
 375 {
 376         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 377
 378         if (p)
 379                 free_page((unsigned long)p);
 380
 381         mod_timer(&slob_timer, jiffies + HZ);
 382 }