unlink_chunk( av , victim )

/* Take a chunk off a bin list.  */
static void
unlink_chunk (mstate av, mchunkptr p)
{
  if (chunksize (p) != prev_size (next_chunk (p)))
    malloc_printerr ("corrupted size vs. prev_size");

  mchunkptr fd = p->fd;
  mchunkptr bk = p->bk;

  if (__builtin_expect (fd->bk != p || bk->fd != p, 0))
    malloc_printerr ("corrupted double-linked list");

  fd->bk = bk;
  bk->fd = fd;
  if (!in_smallbin_range (chunksize_nomask (p)) && p->fd_nextsize != NULL)
    {
      if (p->fd_nextsize->bk_nextsize != p
	  || p->bk_nextsize->fd_nextsize != p)
	malloc_printerr ("corrupted double-linked list (not small)");

      if (fd->fd_nextsize == NULL)
	{
	  if (p->fd_nextsize == p)
	    fd->fd_nextsize = fd->bk_nextsize = fd;
	  else
	    {
	      fd->fd_nextsize = p->fd_nextsize;
	      fd->bk_nextsize = p->bk_nextsize;
	      p->fd_nextsize->bk_nextsize = fd;
	      p->bk_nextsize->fd_nextsize = fd;
	    }
	}
      else
	{
	  p->fd_nextsize->bk_nextsize = p->bk_nextsize;
	  p->bk_nextsize->fd_nextsize = p->fd_nextsize;
	}
    }
}

large bin处理流程

/* skip scan if empty or largest chunk is too small */
          if ((victim = first (bin)) != bin
	      && (unsigned long) chunksize_nomask (victim)
	        >= (unsigned long) (nb))
            {
              victim = victim->bk_nextsize;
              while (((unsigned long) (size = chunksize (victim)) <
                      (unsigned long) (nb)))
                victim = victim->bk_nextsize;

              /* Avoid removing the first entry for a size so that the skip
                 list does not have to be rerouted.  */
              if (victim != last (bin)
		  && chunksize_nomask (victim)
		    == chunksize_nomask (victim->fd))
                victim = victim->fd;

              remainder_size = size - nb;
              unlink_chunk (av, victim);

              /* Exhaust */
              if (remainder_size < MINSIZE)
                {
                  set_inuse_bit_at_offset (victim, size);
                  if (av != &main_arena)
		    set_non_main_arena (victim);
                }
              /* Split */
              else
                {
                  remainder = chunk_at_offset (victim, nb);
                  /* We cannot assume the unsorted list is empty and therefore
                     have to perform a complete insert here.  */
                  bck = unsorted_chunks (av);
                  fwd = bck->fd;
		  if (__glibc_unlikely (fwd->bk != bck))
		    malloc_printerr ("malloc(): corrupted unsorted chunks");
                  remainder->bk = bck;
                  remainder->fd = fwd;
                  bck->fd = remainder;
                  fwd->bk = remainder;
                  if (!in_smallbin_range (remainder_size))
                    {
                      remainder->fd_nextsize = NULL;
                      remainder->bk_nextsize = NULL;
                    }
                  set_head (victim, nb | PREV_INUSE |
                            (av != &main_arena ? NON_MAIN_ARENA : 0));
                  set_head (remainder, remainder_size | PREV_INUSE);
                  set_foot (remainder, remainder_size);
                }
              check_malloced_chunk (av, victim, nb);
              void *p = chunk2mem (victim);
              alloc_perturb (p, bytes);
              return p;
            }