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 void kfree(const void *block)
 194 {
 195         bigblock_t *bb, **last = &bigblocks;
 196         unsigned long flags;
 197
 198         if (!block)
 199                 return;
 200
 201         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 202                 /* might be on the big block list */
 203                 spin_lock_irqsave(&block_lock, flags);
 204                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 205                         if (bb->pages == block) {
 206                                 *last = bb->next;
 207                                 spin_unlock_irqrestore(&block_lock, flags);
 208                                 free_pages((unsigned long)block, bb->order);
 209                                 slob_free(bb, sizeof(bigblock_t));
 210                                 return;
 211                         }
 212                 }
 213                 spin_unlock_irqrestore(&block_lock, flags);
 214         }
 215
 216         slob_free((slob_t *)block - 1, 0);
 217         return;
 218 }
 219
 220 EXPORT_SYMBOL(kfree);
 221
 222 unsigned int ksize(const void *block)
 223 {
 224         bigblock_t *bb;
 225         unsigned long flags;
 226
 227         if (!block)
 228                 return 0;
 229
 230         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 231                 spin_lock_irqsave(&block_lock, flags);
 232                 for (bb = bigblocks; bb; bb = bb->next)
 233                         if (bb->pages == block) {
 234                                 spin_unlock_irqrestore(&slob_lock, flags);
 235                                 return PAGE_SIZE << bb->order;
 236                         }
 237                 spin_unlock_irqrestore(&block_lock, flags);
 238         }
 239
 240         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 241 }
 242
 243 struct kmem_cache {
 244         unsigned int size, align;
 245         const char *name;
 246         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 247         void (*dtor)(void *, struct kmem_cache *, unsigned long);
 248 };
 249
 250 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 251         size_t align, unsigned long flags,
 252         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 253         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 254 {
 255         struct kmem_cache *c;
 256
 257         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 258
 259         if (c) {
 260                 c->name = name;
 261                 c->size = size;
 262                 c->ctor = ctor;
 263                 c->dtor = dtor;
 264                 /* ignore alignment unless it's forced */
 265                 c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 266                 if (c->align < align)
 267                         c->align = align;
 268         }
 269
 270         return c;
 271 }
 272 EXPORT_SYMBOL(kmem_cache_create);
 273
 274 void kmem_cache_destroy(struct kmem_cache *c)
 275 {
 276         slob_free(c, sizeof(struct kmem_cache));
 277 }
 278 EXPORT_SYMBOL(kmem_cache_destroy);
 279
 280 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 281 {
 282         void *b;
 283
 284         if (c->size < PAGE_SIZE)
 285                 b = slob_alloc(c->size, flags, c->align);
 286         else
 287                 b = (void *)__get_free_pages(flags, find_order(c->size));
 288
 289         if (c->ctor)
 290                 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
 291
 292         return b;
 293 }
 294 EXPORT_SYMBOL(kmem_cache_alloc);
 295
 296 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 297 {
 298         void *ret = kmem_cache_alloc(c, flags);
 299         if (ret)
 300                 memset(ret, 0, c->size);
 301
 302         return ret;
 303 }
 304 EXPORT_SYMBOL(kmem_cache_zalloc);
 305
 306 void kmem_cache_free(struct kmem_cache *c, void *b)
 307 {
 308         if (c->dtor)
 309                 c->dtor(b, c, 0);
 310
 311         if (c->size < PAGE_SIZE)
 312                 slob_free(b, c->size);
 313         else
 314                 free_pages((unsigned long)b, find_order(c->size));
 315 }
 316 EXPORT_SYMBOL(kmem_cache_free);
 317
 318 unsigned int kmem_cache_size(struct kmem_cache *c)
 319 {
 320         return c->size;
 321 }
 322 EXPORT_SYMBOL(kmem_cache_size);
 323
 324 const char *kmem_cache_name(struct kmem_cache *c)
 325 {
 326         return c->name;
 327 }
 328 EXPORT_SYMBOL(kmem_cache_name);
 329
 330 static struct timer_list slob_timer = TIMER_INITIALIZER(
 331         (void (*)(unsigned long))slob_timer_cbk, 0, 0);
 332
 333 int kmem_cache_shrink(struct kmem_cache *d)
 334 {
 335         return 0;
 336 }
 337 EXPORT_SYMBOL(kmem_cache_shrink);
 338
 339 int kmem_ptr_validate(struct kmem_cache *a, const void *b)
 340 {
 341         return 0;
 342 }
 343
 344 void __init kmem_cache_init(void)
 345 {
 346         slob_timer_cbk();
 347 }
 348
 349 static void slob_timer_cbk(void)
 350 {
 351         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 352
 353         if (p)
 354                 free_page((unsigned long)p);
 355
 356         mod_timer(&slob_timer, jiffies + HZ);
 357 }