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
  64 static void *slob_alloc(size_t size, gfp_t gfp, int align)
  65 {
  66         slob_t *prev, *cur, *aligned = 0;
  67         int delta = 0, units = SLOB_UNITS(size);
  68         unsigned long flags;
  69
  70         spin_lock_irqsave(&slob_lock, flags);
  71         prev = slobfree;
  72         for (cur = prev->next; ; prev = cur, cur = cur->next) {
  73                 if (align) {
  74                         aligned = (slob_t *)ALIGN((unsigned long)cur, align);
  75                         delta = aligned - cur;
  76                 }
  77                 if (cur->units >= units + delta) { /* room enough? */
  78                         if (delta) { /* need to fragment head to align? */
  79                                 aligned->units = cur->units - delta;
  80                                 aligned->next = cur->next;
  81                                 cur->next = aligned;
  82                                 cur->units = delta;
  83                                 prev = cur;
  84                                 cur = aligned;
  85                         }
  86
  87                         if (cur->units == units) /* exact fit? */
  88                                 prev->next = cur->next; /* unlink */
  89                         else { /* fragment */
  90                                 prev->next = cur + units;
  91                                 prev->next->units = cur->units - units;
  92                                 prev->next->next = cur->next;
  93                                 cur->units = units;
  94                         }
  95
  96                         slobfree = prev;
  97                         spin_unlock_irqrestore(&slob_lock, flags);
  98                         return cur;
  99                 }
 100                 if (cur == slobfree) {
 101                         spin_unlock_irqrestore(&slob_lock, flags);
 102
 103                         if (size == PAGE_SIZE) /* trying to shrink arena? */
 104                                 return 0;
 105
 106                         cur = (slob_t *)__get_free_page(gfp);
 107                         if (!cur)
 108                                 return 0;
 109
 110                         slob_free(cur, PAGE_SIZE);
 111                         spin_lock_irqsave(&slob_lock, flags);
 112                         cur = slobfree;
 113                 }
 114         }
 115 }
 116
 117 static void slob_free(void *block, int size)
 118 {
 119         slob_t *cur, *b = (slob_t *)block;
 120         unsigned long flags;
 121
 122         if (!block)
 123                 return;
 124
 125         if (size)
 126                 b->units = SLOB_UNITS(size);
 127
 128         /* Find reinsertion point */
 129         spin_lock_irqsave(&slob_lock, flags);
 130         for (cur = slobfree; !(b > cur && b < cur->next); cur = cur->next)
 131                 if (cur >= cur->next && (b > cur || b < cur->next))
 132                         break;
 133
 134         if (b + b->units == cur->next) {
 135                 b->units += cur->next->units;
 136                 b->next = cur->next->next;
 137         } else
 138                 b->next = cur->next;
 139
 140         if (cur + cur->units == b) {
 141                 cur->units += b->units;
 142                 cur->next = b->next;
 143         } else
 144                 cur->next = b;
 145
 146         slobfree = cur;
 147
 148         spin_unlock_irqrestore(&slob_lock, flags);
 149 }
 150
 151 static int FASTCALL(find_order(int size));
 152 static int fastcall find_order(int size)
 153 {
 154         int order = 0;
 155         for ( ; size > 4096 ; size >>=1)
 156                 order++;
 157         return order;
 158 }
 159
 160 void *kmalloc(size_t size, gfp_t gfp)
 161 {
 162         slob_t *m;
 163         bigblock_t *bb;
 164         unsigned long flags;
 165
 166         if (size < PAGE_SIZE - SLOB_UNIT) {
 167                 m = slob_alloc(size + SLOB_UNIT, gfp, 0);
 168                 return m ? (void *)(m + 1) : 0;
 169         }
 170
 171         bb = slob_alloc(sizeof(bigblock_t), gfp, 0);
 172         if (!bb)
 173                 return 0;
 174
 175         bb->order = find_order(size);
 176         bb->pages = (void *)__get_free_pages(gfp, bb->order);
 177
 178         if (bb->pages) {
 179                 spin_lock_irqsave(&block_lock, flags);
 180                 bb->next = bigblocks;
 181                 bigblocks = bb;
 182                 spin_unlock_irqrestore(&block_lock, flags);
 183                 return bb->pages;
 184         }
 185
 186         slob_free(bb, sizeof(bigblock_t));
 187         return 0;
 188 }
 189
 190 EXPORT_SYMBOL(kmalloc);
 191
 192 void kfree(const void *block)
 193 {
 194         bigblock_t *bb, **last = &bigblocks;
 195         unsigned long flags;
 196
 197         if (!block)
 198                 return;
 199
 200         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 201                 /* might be on the big block list */
 202                 spin_lock_irqsave(&block_lock, flags);
 203                 for (bb = bigblocks; bb; last = &bb->next, bb = bb->next) {
 204                         if (bb->pages == block) {
 205                                 *last = bb->next;
 206                                 spin_unlock_irqrestore(&block_lock, flags);
 207                                 free_pages((unsigned long)block, bb->order);
 208                                 slob_free(bb, sizeof(bigblock_t));
 209                                 return;
 210                         }
 211                 }
 212                 spin_unlock_irqrestore(&block_lock, flags);
 213         }
 214
 215         slob_free((slob_t *)block - 1, 0);
 216         return;
 217 }
 218
 219 EXPORT_SYMBOL(kfree);
 220
 221 unsigned int ksize(const void *block)
 222 {
 223         bigblock_t *bb;
 224         unsigned long flags;
 225
 226         if (!block)
 227                 return 0;
 228
 229         if (!((unsigned long)block & (PAGE_SIZE-1))) {
 230                 spin_lock_irqsave(&block_lock, flags);
 231                 for (bb = bigblocks; bb; bb = bb->next)
 232                         if (bb->pages == block) {
 233                                 spin_unlock_irqrestore(&slob_lock, flags);
 234                                 return PAGE_SIZE << bb->order;
 235                         }
 236                 spin_unlock_irqrestore(&block_lock, flags);
 237         }
 238
 239         return ((slob_t *)block - 1)->units * SLOB_UNIT;
 240 }
 241
 242 struct kmem_cache {
 243         unsigned int size, align;
 244         const char *name;
 245         void (*ctor)(void *, struct kmem_cache *, unsigned long);
 246         void (*dtor)(void *, struct kmem_cache *, unsigned long);
 247 };
 248
 249 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 250         size_t align, unsigned long flags,
 251         void (*ctor)(void*, struct kmem_cache *, unsigned long),
 252         void (*dtor)(void*, struct kmem_cache *, unsigned long))
 253 {
 254         struct kmem_cache *c;
 255
 256         c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
 257
 258         if (c) {
 259                 c->name = name;
 260                 c->size = size;
 261                 c->ctor = ctor;
 262                 c->dtor = dtor;
 263                 /* ignore alignment unless it's forced */
 264                 c->align = (flags & SLAB_MUST_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
 265                 if (c->align < align)
 266                         c->align = align;
 267         }
 268
 269         return c;
 270 }
 271 EXPORT_SYMBOL(kmem_cache_create);
 272
 273 void kmem_cache_destroy(struct kmem_cache *c)
 274 {
 275         slob_free(c, sizeof(struct kmem_cache));
 276 }
 277 EXPORT_SYMBOL(kmem_cache_destroy);
 278
 279 void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
 280 {
 281         void *b;
 282
 283         if (c->size < PAGE_SIZE)
 284                 b = slob_alloc(c->size, flags, c->align);
 285         else
 286                 b = (void *)__get_free_pages(flags, find_order(c->size));
 287
 288         if (c->ctor)
 289                 c->ctor(b, c, SLAB_CTOR_CONSTRUCTOR);
 290
 291         return b;
 292 }
 293 EXPORT_SYMBOL(kmem_cache_alloc);
 294
 295 void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
 296 {
 297         void *ret = kmem_cache_alloc(c, flags);
 298         if (ret)
 299                 memset(ret, 0, c->size);
 300
 301         return ret;
 302 }
 303 EXPORT_SYMBOL(kmem_cache_zalloc);
 304
 305 void kmem_cache_free(struct kmem_cache *c, void *b)
 306 {
 307         if (c->dtor)
 308                 c->dtor(b, c, 0);
 309
 310         if (c->size < PAGE_SIZE)
 311                 slob_free(b, c->size);
 312         else
 313                 free_pages((unsigned long)b, find_order(c->size));
 314 }
 315 EXPORT_SYMBOL(kmem_cache_free);
 316
 317 unsigned int kmem_cache_size(struct kmem_cache *c)
 318 {
 319         return c->size;
 320 }
 321 EXPORT_SYMBOL(kmem_cache_size);
 322
 323 const char *kmem_cache_name(struct kmem_cache *c)
 324 {
 325         return c->name;
 326 }
 327 EXPORT_SYMBOL(kmem_cache_name);
 328
 329 static struct timer_list slob_timer = TIMER_INITIALIZER(
 330         (void (*)(unsigned long))kmem_cache_init, 0, 0);
 331
 332 void kmem_cache_init(void)
 333 {
 334         void *p = slob_alloc(PAGE_SIZE, 0, PAGE_SIZE-1);
 335
 336         if (p)
 337                 free_page((unsigned long)p);
 338
 339         mod_timer(&slob_timer, jiffies + HZ);
 340 }