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 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 void kfree(const void *block)
 185 {
 186         bigblock_t *bb, **last = &bigblocks;
 187         unsigned long flags;
 188
 189         if (!block)
 190                 return;
 191
 192         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 193                 /* might be on the big block list */
 194                 spin_lock_irqsave(&block_lock, flags);
 195                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 196                         if (bb->pages == block) {
 197                                 *last = bb->next;
 198                                 spin_unlock_irqrestore(&block_lock, flags);
 199                                 free_pages((unsigned long)block, bb->order);
 200                                 slob_free(bb, sizeof(bigblock_t));
 201                                 return;
 202                         }
 203                 }
 204                 spin_unlock_irqrestore(&block_lock, flags);
 205         }
 206
 207         slob_free((slob_t *)block - 1, 0);
 208         return;
 209 }
 210
 211 EXPORT_SYMBOL(kfree);
 212
 213 unsigned int ksize(const void *block)
 214 {
 215         bigblock_t *bb;
 216         unsigned long flags;
 217
 218         if (!block)
 219                 return 0;
 220
 221         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 222                 spin_lock_irqsave(&block_lock, flags);
 223                 for (bb = bigblocks; bb; bb = bb->next)
 224                         if (bb->pages == block) {
 225                                 spin_unlock_irqrestore(&slob_lock, flags);
 226                                 return PAGE_SIZE << bb->order;
 227                         }
 228                 spin_unlock_irqrestore(&block_lock, flags);
 229         }
 230
 231         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 232 }
 233
 234 struct kmem_cache {
 235         unsigned int size, align;
 236         const char *name;
 237         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 238         void (*dtor)(void *, struct kmem_cache *, unsigned long);
 239 };
 240
 241 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 242         size_t align, unsigned long flags,
 243         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 244         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 245 {
 246         struct kmem_cache *c;
 247
 248         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 249
 250         if (c) {
 251                 c->name = name;
 252                 c->size = size;
 253                 c->ctor = ctor;
 254                 c->dtor = dtor;
 255                 /* ignore alignment unless it's forced */
 256                 c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 257                 if (c->align < align)
 258                         c->align = align;
 259         }
 260
 261         return c;
 262 }
 263 EXPORT_SYMBOL(kmem_cache_create);
 264
 265 void kmem_cache_destroy(struct kmem_cache *c)
 266 {
 267         slob_free(c, sizeof(struct kmem_cache));
 268 }
 269 EXPORT_SYMBOL(kmem_cache_destroy);
 270
 271 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 272 {
 273         void *b;
 274
 275         if (c->size < PAGE_SIZE)
 276                 b = slob_alloc(c->size, flags, c->align);
 277         else
 278                 b = (void *)__get_free_pages(flags, get_order(c->size));
 279
 280         if (c->ctor)
 281                 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
 282
 283         return b;
 284 }
 285 EXPORT_SYMBOL(kmem_cache_alloc);
 286
 287 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 288 {
 289         void *ret = kmem_cache_alloc(c, flags);
 290         if (ret)
 291                 memset(ret, 0, c->size);
 292
 293         return ret;
 294 }
 295 EXPORT_SYMBOL(kmem_cache_zalloc);
 296
 297 void kmem_cache_free(struct kmem_cache *c, void *b)
 298 {
 299         if (c->dtor)
 300                 c->dtor(b, c, 0);
 301
 302         if (c->size < PAGE_SIZE)
 303                 slob_free(b, c->size);
 304         else
 305                 free_pages((unsigned long)b, get_order(c->size));
 306 }
 307 EXPORT_SYMBOL(kmem_cache_free);
 308
 309 unsigned int kmem_cache_size(struct kmem_cache *c)
 310 {
 311         return c->size;
 312 }
 313 EXPORT_SYMBOL(kmem_cache_size);
 314
 315 const char *kmem_cache_name(struct kmem_cache *c)
 316 {
 317         return c->name;
 318 }
 319 EXPORT_SYMBOL(kmem_cache_name);
 320
 321 static struct timer_list slob_timer = TIMER_INITIALIZER(
 322         (void (*)(unsigned long))slob_timer_cbk, 0, 0);
 323
 324 int kmem_cache_shrink(struct kmem_cache *d)
 325 {
 326         return 0;
 327 }
 328 EXPORT_SYMBOL(kmem_cache_shrink);
 329
 330 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
 331 {
 332         return 0;
 333 }
 334
 335 void __init kmem_cache_init(void)
 336 {
 337         slob_timer_cbk();
 338 }
 339
 340 static void slob_timer_cbk(void)
 341 {
 342         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 343
 344         if (p)
 345                 free_page((unsigned long)p);
 346
 347         mod_timer(&slob_timer, jiffies + HZ);
 348 }