Try to Study Rmap.

fork_anon_vma.c

/**
 * Rmap Study in Linux Kernel v5.1 
 * 
 * [kernel/fork.c -> rmap.c] rmap init routine.
 *
 * do_fork          		[kernel/fork.c]
 * - _do_fork       		[kernel/fork.c]
 * -- copy_process  		[kernel/fork.c]
 * --- copy_mm      		[kernel/fork.c]
 *
 * ---- static struct mm_struct *dup_mm(struct task_struct *tsk)	[kernel/fork.c]
 * 	
 * 	struct mm_struct *mm, *oldmm = current->mm;
	int err;

	mm = allocate_mm();
	
	// ...
	
 * 	if (!mm_init(mm, tsk, mm->user_ns))
		goto fail_nomem;
 * ...
 *
 * See Below source code.
 * 
 * ----- dup_mmap   		[kernel/fork.c]
 * tmp = vm_area_dup(mpnt); 
 * this make (struct vm_area_struct *vma) new VMA
 * 
 * then,
 *
 * Call anon_vma_prepare(new VMA) [mm/rmap.c]
 * OR
 * Call anon_vma_fork(new VMA, parent VMA) [mm/rmap.c]
 */

#ifdef CONFIG_MMU
static __latent_entropy int dup_mmap(struct mm_struct *mm,
					struct mm_struct *oldmm)

	// ...
	
	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
		
		// ...
		
		tmp = vm_area_dup(mpnt);
		if (!tmp)
			goto fail_nomem;
		retval = vma_dup_policy(mpnt, tmp);
		if (retval)
			goto fail_nomem_policy;
		tmp->vm_mm = mm;
		retval = dup_userfaultfd(tmp, &uf);
		if (retval)
			goto fail_nomem_anon_vma_fork;
		if (tmp->vm_flags & VM_WIPEONFORK) {
			/* VM_WIPEONFORK gets a clean slate in the child. */
			tmp->anon_vma = NULL;
			if (anon_vma_prepare(tmp))
				goto fail_nomem_anon_vma_fork;
		} else if (anon_vma_fork(tmp, mpnt))
			goto fail_nomem_anon_vma_fork;
		
		// ... file ...
	}	
// ...

fail_nomem_anon_vma_fork:
	mpol_put(vma_policy(tmp));

// ...

}