malloc.c

   1 #include <stdlib.h>
   2 #include <sys/mman.h>
   3
   4 #define MSET_SIZE               (1 << 15)
   5 #define MMAP_MIN                (1 << 12)
   6
   7 struct mset {
   8         int refs;
   9         int size;
  10 };
  11
  12 struct mem {
  13         int size;
  14         struct mset *mset;
  15 };
  16
  17 static struct mset *pool;
  18
  19 static void mk_pool(void)
  20 {
  21         if (pool && !pool->refs) {
  22                 pool->size = sizeof(*pool);
  23                 return;
  24         }
  25         pool = mmap(NULL, MSET_SIZE, PROT_READ | PROT_WRITE,
  26                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  27         if (pool == MAP_FAILED) {
  28                 pool = NULL;
  29                 return;
  30         }
  31         pool->size = sizeof(*pool);
  32         pool->refs = 0;
  33 }
  34
  35 void *malloc(int n)
  36 {
  37         struct mem *mem;
  38         n += sizeof(*mem);
  39         if (n >= MMAP_MIN) {
  40                 mem = mmap(NULL, n, PROT_READ | PROT_WRITE,
  41                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  42                 if (mem == MAP_FAILED)
  43                         return NULL;
  44                 mem->size = n;
  45                 mem->mset = NULL;
  46                 return (void *) mem + sizeof(*mem);
  47         }
  48         if (!pool || MSET_SIZE - pool->size < n)
  49                 mk_pool();
  50         if (!pool)
  51                 return NULL;
  52         mem = (void *) pool + pool->size;
  53         mem->mset = pool;
  54         mem->size = n;
  55         pool->refs++;
  56         pool->size += (n + 7) & ~7;
  57         return (void *) mem + sizeof(*mem);
  58 }
  59
  60 void free(void *v)
  61 {
  62         struct mem *mem = v - sizeof(struct mem);
  63         if (mem->mset) {
  64                 struct mset *mset = mem->mset;
  65                 mset->refs--;
  66                 if (!mset->refs && mset != pool)
  67                         munmap(mset, mset->size);
  68         } else {
  69                 munmap(mem, mem->size);
  70         }
  71 }