root/mm/kmalloc.c

/* */

DEFINITIONS

1. kmalloc_init
2. get_order
3. kmalloc
4. kfree_s

   1 /*
   2  *  linux/mm/kmalloc.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds & Roger Wolff.
   5  *
   6  *  Written by R.E. Wolff Sept/Oct '93.
   7  *
   8  */
   9 
  10 #include <linux/mm.h>
  11 #include <asm/system.h>
  12 #include <linux/delay.h>
  13 
  14 #define GFP_LEVEL_MASK 0xf
  15 
  16 /* I want this low enough for a while to catch errors.
  17    I want this number to be increased in the near future:
  18         loadable device drivers should use this function to get memory */
  19 
  20 #define MAX_KMALLOC_K 4
  21 
  22 
  23 /* This defines how many times we should try to allocate a free page before
  24    giving up. Normally this shouldn't happen at all. */
  25 #define MAX_GET_FREE_PAGE_TRIES 4
  26 
  27 
  28 /* Private flags. */
  29 
  30 #define MF_USED 0xffaa0055
  31 #define MF_FREE 0x0055ffaa
  32 
  33 
  34 /* 
  35  * Much care has gone into making these routines in this file reentrant.
  36  *
  37  * The fancy bookkeeping of nbytesmalloced and the like are only used to
  38  * report them to the user (oooohhhhh, aaaaahhhhh....) are not 
  39  * protected by cli(). (If that goes wrong. So what?)
  40  *
  41  * These routines restore the interrupt status to allow calling with ints
  42  * off. 
  43  */
  44 
  45 /* 
  46  * A block header. This is in front of every malloc-block, whether free or not.
  47  */
  48 struct block_header {
  49         unsigned long bh_flags;
  50         union {
  51                 unsigned long ubh_length;
  52                 struct block_header *fbh_next;
  53         } vp;
  54 };
  55 
  56 
  57 #define bh_length vp.ubh_length
  58 #define bh_next   vp.fbh_next
  59 #define BH(p) ((struct block_header *)(p))
  60 
  61 
  62 /* 
  63  * The page descriptor is at the front of every page that malloc has in use. 
  64  */
  65 struct page_descriptor {
  66         struct page_descriptor *next;
  67         struct block_header *firstfree;
  68         int order;
  69         int nfree;
  70 };
  71 
  72 
  73 #define PAGE_DESC(p) ((struct page_descriptor *)(((unsigned long)(p)) & PAGE_MASK))
  74 
  75 
  76 /*
  77  * A size descriptor describes a specific class of malloc sizes.
  78  * Each class of sizes has its own freelist.
  79  */
  80 struct size_descriptor {
  81         struct page_descriptor *firstfree;
  82         int size;
  83         int nblocks;
  84 
  85         int nmallocs;
  86         int nfrees;
  87         int nbytesmalloced;
  88         int npages;
  89 };
  90 
  91 
  92 struct size_descriptor sizes[] = { 
  93         { NULL,  32,127, 0,0,0,0 },
  94         { NULL,  64, 63, 0,0,0,0 },
  95         { NULL, 128, 31, 0,0,0,0 },
  96         { NULL, 252, 16, 0,0,0,0 },
  97         { NULL, 508,  8, 0,0,0,0 },
  98         { NULL,1020,  4, 0,0,0,0 },
  99         { NULL,2040,  2, 0,0,0,0 },
 100         { NULL,4080,  1, 0,0,0,0 },
 101         { NULL,   0,  0, 0,0,0,0 }
 102 };
 103 
 104 
 105 #define NBLOCKS(order)          (sizes[order].nblocks)
 106 #define BLOCKSIZE(order)        (sizes[order].size)
 107 
 108 
 109 
 110 long kmalloc_init (long start_mem,long end_mem)
     /*  */
 111 {
 112         int order;
 113 
 114 /* 
 115  * Check the static info array. Things will blow up terribly if it's
 116  * incorrect. This is a late "compile time" check.....
 117  */
 118 for (order = 0;BLOCKSIZE(order);order++)
 119     {
 120     if ((NBLOCKS (order)*BLOCKSIZE(order) + sizeof (struct page_descriptor)) >
 121         PAGE_SIZE) 
 122         {
 123         printk ("Cannot use %d bytes out of %d in order = %d block mallocs\n",
 124                 NBLOCKS (order) * BLOCKSIZE(order) + 
 125                         sizeof (struct page_descriptor),
 126                 (int) PAGE_SIZE,
 127                 BLOCKSIZE (order));
 128         panic ("This only happens if someone messes with kmalloc");
 129         }
 130     }
 131 return start_mem;
 132 }
 133 
 134 
 135 
 136 int get_order (int size)
     /*  */
 137 {
 138         int order;
 139 
 140         /* Add the size of the header */
 141         size += sizeof (struct block_header); 
 142         for (order = 0;BLOCKSIZE(order);order++)
 143                 if (size <= BLOCKSIZE (order))
 144                         return order; 
 145         return -1;
 146 }
 147 
 148 void * kmalloc (size_t size, int priority)
     /*  */
 149 {
 150         unsigned long flags;
 151         int order,tries,i,sz;
 152         struct block_header *p;
 153         struct page_descriptor *page;
 154 
 155 /* Sanity check... */
 156         if (intr_count && priority != GFP_ATOMIC) {
 157                 static int count = 0;
 158                 if (++count < 5) {
 159                         printk("kmalloc called nonatomically from interrupt %08lx\n",
 160                                 ((unsigned long *)&size)[-1]);
 161                         priority = GFP_ATOMIC;
 162                 }
 163         }
 164 if (size > MAX_KMALLOC_K * 1024) 
 165      {
 166      printk ("kmalloc: I refuse to allocate %d bytes (for now max = %d).\n",
 167                 size,MAX_KMALLOC_K*1024);
 168      return (NULL);
 169      }
 170 
 171 order = get_order (size);
 172 if (order < 0)
 173     {
 174     printk ("kmalloc of too large a block (%d bytes).\n",size);
 175     return (NULL);
 176     }
 177 
 178 save_flags(flags);
 179 
 180 /* It seems VERY unlikely to me that it would be possible that this 
 181    loop will get executed more than once. */
 182 tries = MAX_GET_FREE_PAGE_TRIES; 
 183 while (tries --)
 184     {
 185     /* Try to allocate a "recently" freed memory block */
 186     cli ();
 187     if ((page = sizes[order].firstfree) &&
 188         (p    =  page->firstfree))
 189         {
 190         if (p->bh_flags == MF_FREE)
 191             {
 192             page->firstfree = p->bh_next;
 193             page->nfree--;
 194             if (!page->nfree)
 195                 {
 196                 sizes[order].firstfree = page->next;
 197                 page->next = NULL;
 198                 }
 199             restore_flags(flags);
 200 
 201             sizes [order].nmallocs++;
 202             sizes [order].nbytesmalloced += size;
 203             p->bh_flags =  MF_USED; /* As of now this block is officially in use */
 204             p->bh_length = size;
 205             return p+1; /* Pointer arithmetic: increments past header */
 206             }
 207         printk ("Problem: block on freelist at %08lx isn't free.\n",(long)p);
 208         return (NULL);
 209         }
 210     restore_flags(flags);
 211 
 212 
 213     /* Now we're in trouble: We need to get a new free page..... */
 214 
 215     sz = BLOCKSIZE(order); /* sz is the size of the blocks we're dealing with */
 216 
 217     /* This can be done with ints on: This is private to this invocation */
 218     page = (struct page_descriptor *) __get_free_page (priority & GFP_LEVEL_MASK);
 219     if (!page) {
 220         static unsigned long last = 0;
 221         if (last + 10*HZ < jiffies) {
 222                 last = jiffies;
 223                 printk ("Couldn't get a free page.....\n");
 224         }
 225         return NULL;
 226     }
 227 #if 0
 228     printk ("Got page %08x to use for %d byte mallocs....",(long)page,sz);
 229 #endif
 230     sizes[order].npages++;
 231 
 232     /* Loop for all but last block: */
 233     for (i=NBLOCKS(order),p=BH (page+1);i > 1;i--,p=p->bh_next) 
 234         {
 235         p->bh_flags = MF_FREE;
 236         p->bh_next = BH ( ((long)p)+sz);
 237         }
 238     /* Last block: */
 239     p->bh_flags = MF_FREE;
 240     p->bh_next = NULL;
 241 
 242     page->order = order;
 243     page->nfree = NBLOCKS(order); 
 244     page->firstfree = BH(page+1);
 245 #if 0
 246     printk ("%d blocks per page\n",page->nfree);
 247 #endif
 248     /* Now we're going to muck with the "global" freelist for this size:
 249        this should be uniterruptible */
 250     cli ();
 251     /* 
 252      * sizes[order].firstfree used to be NULL, otherwise we wouldn't be
 253      * here, but you never know.... 
 254      */
 255     page->next = sizes[order].firstfree;
 256     sizes[order].firstfree = page;
 257     restore_flags(flags);
 258     }
 259 
 260 /* Pray that printk won't cause this to happen again :-) */
 261 
 262 printk ("Hey. This is very funny. I tried %d times to allocate a whole\n"
 263         "new page for an object only %d bytes long, but some other process\n"
 264         "beat me to actually allocating it. Also note that this 'error'\n"
 265         "message is soooo very long to catch your attention. I'd appreciate\n"
 266         "it if you'd be so kind as to report what conditions caused this to\n"
 267         "the author of this kmalloc: wolff@dutecai.et.tudelft.nl.\n"
 268         "(Executive summary: This can't happen)\n", 
 269                 MAX_GET_FREE_PAGE_TRIES,
 270                 size);
 271 return NULL;
 272 }
 273 
 274 
 275 void kfree_s (void *ptr,int size)
     /*  */
 276 {
 277 unsigned long flags;
 278 int order;
 279 register struct block_header *p=((struct block_header *)ptr) -1;
 280 struct page_descriptor *page,*pg2;
 281 
 282 page = PAGE_DESC (p);
 283 order = page->order;
 284 if ((order < 0) || 
 285     (order > sizeof (sizes)/sizeof (sizes[0])) ||
 286     (((long)(page->next)) & ~PAGE_MASK) ||
 287     (p->bh_flags != MF_USED))
 288     {
 289     printk ("kfree of non-kmalloced memory: %p, next= %p, order=%d\n",
 290                 p, page->next, page->order);
 291     return;
 292     }
 293 if (size &&
 294     size != p->bh_length)
 295     {
 296     printk ("Trying to free pointer at %p with wrong size: %d instead of %lu.\n",
 297         p,size,p->bh_length);
 298     return;
 299     }
 300 size = p->bh_length;
 301 p->bh_flags = MF_FREE; /* As of now this block is officially free */
 302 save_flags(flags);
 303 cli ();
 304 p->bh_next = page->firstfree;
 305 page->firstfree = p;
 306 page->nfree ++;
 307 
 308 if (page->nfree == 1)
 309    { /* Page went from full to one free block: put it on the freelist */
 310    if (page->next)
 311         {
 312         printk ("Page %p already on freelist dazed and confused....\n", page);
 313         }
 314    else
 315         {
 316         page->next = sizes[order].firstfree;
 317         sizes[order].firstfree = page;
 318         }
 319    }
 320 
 321 /* If page is completely free, free it */
 322 if (page->nfree == NBLOCKS (page->order))
 323     {
 324 #if 0
 325     printk ("Freeing page %08x.\n", (long)page);
 326 #endif
 327     if (sizes[order].firstfree == page)
 328         {
 329         sizes[order].firstfree = page->next;
 330         }
 331     else
 332         {
 333         for (pg2=sizes[order].firstfree;
 334                 (pg2 != NULL) && (pg2->next != page);
 335                         pg2=pg2->next)
 336             /* Nothing */;
 337         if (pg2 != NULL)
 338             pg2->next = page->next;
 339         else
 340             printk ("Ooops. page %p doesn't show on freelist.\n", page);
 341         }
 342     free_page ((long)page);
 343     }
 344 restore_flags(flags);
 345 
 346 sizes[order].nfrees++;      /* Noncritical (monitoring) admin stuff */
 347 sizes[order].nbytesmalloced -= size;
 348 }

/* */