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 #include <linux/rcupdate.h>
  39
  40 struct slob_block {
  41         int units;
  42         struct slob_block *next;
  43 };
  44 typedef struct slob_block slob_t;
  45
  46 #define SLOB_UNIT sizeof(slob_t)
  47 #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
  48 #define SLOB_ALIGN L1_CACHE_BYTES
  49
  50 struct bigblock {
  51         int order;
  52         void *pages;
  53         struct bigblock *next;
  54 };
  55 typedef struct bigblock bigblock_t;
  56
  57 /*
  58  * struct slob_rcu is inserted at the tail of allocated slob blocks, which
  59  * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
  60  * the block using call_rcu.
  61  */
  62 struct slob_rcu {
  63         struct rcu_head head;
  64         int size;
  65 };
  66
  67 static slob_t arena = { .next = &arena, .units = 1 };
  68 static slob_t *slobfree = &arena;
  69 static bigblock_t *bigblocks;
  70 static DEFINE_SPINLOCK(slob_lock);
  71 static DEFINE_SPINLOCK(block_lock);
  72
  73 static void slob_free(void *b, int size);
  74 static void slob_timer_cbk(void);
  75
  76
  77 static void *slob_alloc(size_t size, gfp_t gfp, int align)
  78 {
  79         slob_t *prev, *cur, *aligned = 0;
  80         int delta = 0, units = SLOB_UNITS(size);
  81         unsigned long flags;
  82
  83         spin_lock_irqsave(&slob_lock, flags);
  84         prev = slobfree;
  85         for (cur = prev->next; ; prev = cur, cur = cur->next) {
  86                 if (align) {
  87                         aligned = (slob_t *)ALIGN((unsigned long)cur, align);
  88                         delta = aligned - cur;
  89                 }
  90                 if (cur->units >= units + delta) { /* room enough? */
  91                         if (delta) { /* need to fragment head to align? */
  92                                 aligned->units = cur->units - delta;
  93                                 aligned->next = cur->next;
  94                                 cur->next = aligned;
  95                                 cur->units = delta;
  96                                 prev = cur;
  97                                 cur = aligned;
  98                         }
  99
 100                         if (cur->units == units) /* exact fit? */
 101                                 prev->next = cur->next; /* unlink */
 102                         else { /* fragment */
 103                                 prev->next = cur + units;
 104                                 prev->next->units = cur->units - units;
 105                                 prev->next->next = cur->next;
 106                                 cur->units = units;
 107                         }
 108
 109                         slobfree = prev;
 110                         spin_unlock_irqrestore(&slob_lock, flags);
 111                         return cur;
 112                 }
 113                 if (cur == slobfree) {
 114                         spin_unlock_irqrestore(&slob_lock, flags);
 115
 116                         if (size == PAGE_SIZE) /* trying to shrink arena? */
 117                                 return 0;
 118
 119                         cur = (slob_t *)__get_free_page(gfp);
 120                         if (!cur)
 121                                 return 0;
 122
 123                         slob_free(cur, PAGE_SIZE);
 124                         spin_lock_irqsave(&slob_lock, flags);
 125                         cur = slobfree;
 126                 }
 127         }
 128 }
 129
 130 static void slob_free(void *block, int size)
 131 {
 132         slob_t *cur, *b = (slob_t *)block;
 133         unsigned long flags;
 134
 135         if (!block)
 136                 return;
 137
 138         if (size)
 139                 b->units = SLOB_UNITS(size);
 140
 141         /* Find reinsertion point */
 142         spin_lock_irqsave(&slob_lock, flags);
 143         for (cur = slobfree; !(b > cur && b < cur->next); cur = cur->next)
 144                 if (cur >= cur->next && (b > cur || b < cur->next))
 145                         break;
 146
 147         if (b + b->units == cur->next) {
 148                 b->units += cur->next->units;
 149                 b->next = cur->next->next;
 150         } else
 151                 b->next = cur->next;
 152
 153         if (cur + cur->units == b) {
 154                 cur->units += b->units;
 155                 cur->next = b->next;
 156         } else
 157                 cur->next = b;
 158
 159         slobfree = cur;
 160
 161         spin_unlock_irqrestore(&slob_lock, flags);
 162 }
 163
 164 void *__kmalloc(size_t size, gfp_t gfp)
 165 {
 166         slob_t *m;
 167         bigblock_t *bb;
 168         unsigned long flags;
 169
 170         if (size < PAGE_SIZE - SLOB_UNIT) {
 171                 m = slob_alloc(size + SLOB_UNIT, gfp, 0);
 172                 return m ? (void *)(m + 1) : 0;
 173         }
 174
 175         bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
 176         if (!bb)
 177                 return 0;
 178
 179         bb->order = get_order(size);
 180         bb->pages = (void *)__get_free_pages(gfp, bb->order);
 181
 182         if (bb->pages) {
 183                 spin_lock_irqsave(&block_lock, flags);
 184                 bb->next = bigblocks;
 185                 bigblocks = bb;
 186                 spin_unlock_irqrestore(&block_lock, flags);
 187                 return bb->pages;
 188         }
 189
 190         slob_free(bb, sizeof(bigblock_t));
 191         return 0;
 192 }
 193 EXPORT_SYMBOL(__kmalloc);
 194
 195 /**
 196  * krealloc - reallocate memory. The contents will remain unchanged.
 197  *
 198  * @p: object to reallocate memory for.
 199  * @new_size: how many bytes of memory are required.
 200  * @flags: the type of memory to allocate.
 201  *
 202  * The contents of the object pointed to are preserved up to the
 203  * lesser of the new and old sizes.  If @p is %NULL, krealloc()
 204  * behaves exactly like kmalloc().  If @size is 0 and @p is not a
 205  * %NULL pointer, the object pointed to is freed.
 206  */
 207 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 208 {
 209         void *ret;
 210
 211         if (unlikely(!p))
 212                 return kmalloc_track_caller(new_size, flags);
 213
 214         if (unlikely(!new_size)) {
 215                 kfree(p);
 216                 return NULL;
 217         }
 218
 219         ret = kmalloc_track_caller(new_size, flags);
 220         if (ret) {
 221                 memcpy(ret, p, min(new_size, ksize(p)));
 222                 kfree(p);
 223         }
 224         return ret;
 225 }
 226 EXPORT_SYMBOL(krealloc);
 227
 228 void kfree(const void *block)
 229 {
 230         bigblock_t *bb, **last = &bigblocks;
 231         unsigned long flags;
 232
 233         if (!block)
 234                 return;
 235
 236         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 237                 /* might be on the big block list */
 238                 spin_lock_irqsave(&block_lock, flags);
 239                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 240                         if (bb->pages == block) {
 241                                 *last = bb->next;
 242                                 spin_unlock_irqrestore(&block_lock, flags);
 243                                 free_pages((unsigned long)block, bb->order);
 244                                 slob_free(bb, sizeof(bigblock_t));
 245                                 return;
 246                         }
 247                 }
 248                 spin_unlock_irqrestore(&block_lock, flags);
 249         }
 250
 251         slob_free((slob_t *)block - 1, 0);
 252         return;
 253 }
 254
 255 EXPORT_SYMBOL(kfree);
 256
 257 size_t ksize(const void *block)
 258 {
 259         bigblock_t *bb;
 260         unsigned long flags;
 261
 262         if (!block)
 263                 return 0;
 264
 265         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 266                 spin_lock_irqsave(&block_lock, flags);
 267                 for (bb = bigblocks; bb; bb = bb->next)
 268                         if (bb->pages == block) {
 269                                 spin_unlock_irqrestore(&slob_lock, flags);
 270                                 return PAGE_SIZE << bb->order;
 271                         }
 272                 spin_unlock_irqrestore(&block_lock, flags);
 273         }
 274
 275         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 276 }
 277
 278 struct kmem_cache {
 279         unsigned int size, align;
 280         unsigned long flags;
 281         const char *name;
 282         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 283 };
 284
 285 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 286         size_t align, unsigned long flags,
 287         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 288         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 289 {
 290         struct kmem_cache *c;
 291
 292         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 293
 294         if (c) {
 295                 c->name = name;
 296                 c->size = size;
 297                 if (flags & SLAB_DESTROY_BY_RCU) {
 298                         /* leave room for rcu footer at the end of object */
 299                         c->size += sizeof(struct slob_rcu);
 300                 }
 301                 c->flags = flags;
 302                 c->ctor = ctor;
 303                 /* ignore alignment unless it's forced */
 304                 c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 305                 if (c->align < align)
 306                         c->align = align;
 307         } else if (flags & SLAB_PANIC)
 308                 panic("Cannot create slab cache %s\n", name);
 309
 310         return c;
 311 }
 312 EXPORT_SYMBOL(kmem_cache_create);
 313
 314 void kmem_cache_destroy(struct kmem_cache *c)
 315 {
 316         slob_free(c, sizeof(struct kmem_cache));
 317 }
 318 EXPORT_SYMBOL(kmem_cache_destroy);
 319
 320 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 321 {
 322         void *b;
 323
 324         if (c->size < PAGE_SIZE)
 325                 b = slob_alloc(c->size, flags, c->align);
 326         else
 327                 b = (void *)__get_free_pages(flags, get_order(c->size));
 328
 329         if (c->ctor)
 330                 c->ctor(b, c, 0);
 331
 332         return b;
 333 }
 334 EXPORT_SYMBOL(kmem_cache_alloc);
 335
 336 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 337 {
 338         void *ret = kmem_cache_alloc(c, flags);
 339         if (ret)
 340                 memset(ret, 0, c->size);
 341
 342         return ret;
 343 }
 344 EXPORT_SYMBOL(kmem_cache_zalloc);
 345
 346 static void __kmem_cache_free(void *b, int size)
 347 {
 348         if (size < PAGE_SIZE)
 349                 slob_free(b, size);
 350         else
 351                 free_pages((unsigned long)b, get_order(size));
 352 }
 353
 354 static void kmem_rcu_free(struct rcu_head *head)
 355 {
 356         struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
 357         void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
 358
 359         __kmem_cache_free(b, slob_rcu->size);
 360 }
 361
 362 void kmem_cache_free(struct kmem_cache *c, void *b)
 363 {
 364         if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
 365                 struct slob_rcu *slob_rcu;
 366                 slob_rcu = b + (c->size - sizeof(struct slob_rcu));
 367                 INIT_RCU_HEAD(&slob_rcu->head);
 368                 slob_rcu->size = c->size;
 369                 call_rcu(&slob_rcu->head, kmem_rcu_free);
 370         } else {
 371                 __kmem_cache_free(b, c->size);
 372         }
 373 }
 374 EXPORT_SYMBOL(kmem_cache_free);
 375
 376 unsigned int kmem_cache_size(struct kmem_cache *c)
 377 {
 378         return c->size;
 379 }
 380 EXPORT_SYMBOL(kmem_cache_size);
 381
 382 const char *kmem_cache_name(struct kmem_cache *c)
 383 {
 384         return c->name;
 385 }
 386 EXPORT_SYMBOL(kmem_cache_name);
 387
 388 static struct timer_list slob_timer = TIMER_INITIALIZER(
 389         (void (*)(unsigned long))slob_timer_cbk, 0, 0);
 390
 391 int kmem_cache_shrink(struct kmem_cache *d)
 392 {
 393         return 0;
 394 }
 395 EXPORT_SYMBOL(kmem_cache_shrink);
 396
 397 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
 398 {
 399         return 0;
 400 }
 401
 402 void __init kmem_cache_init(void)
 403 {
 404         slob_timer_cbk();
 405 }
 406
 407 static void slob_timer_cbk(void)
 408 {
 409         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 410
 411         if (p)
 412                 free_page((unsigned long)p);
 413
 414         mod_timer(&slob_timer, jiffies + HZ);
 415 }