VMEM_SBRK_MINALLOC
if (vmem_sbrk_minalloc < VMEM_SBRK_MINALLOC)
vmem_sbrk_minalloc = VMEM_SBRK_MINALLOC;
size_t vmem_sbrk_minalloc = VMEM_SBRK_MINALLOC; /* minimum allocation */