mempolicy: document {set|get}_policy() vm_ops APIs

	 * writable, if an error is returned it will cause a SIGBUS */

	int (*page_mkwrite)(struct vm_area_struct *vma, struct page *page);

#ifdef CONFIG_NUMA

	/*

	 * set_policy() op must add a reference to any non-NULL @new mempolicy

	 * to hold the policy upon return.  Caller should pass NULL @new to

	 * remove a policy and fall back to surrounding context--i.e. do not

	 * install a MPOL_DEFAULT policy, nor the task or system default

	 * mempolicy.

	 */

	int (*set_policy)(struct vm_area_struct *vma, struct mempolicy *new);

	/*

	 * get_policy() op must add reference [mpol_get()] to any policy at

	 * (vma,addr) marked as MPOL_SHARED.  The shared policy infrastructure

	 * in mm/mempolicy.c will do this automatically.

	 * get_policy() must NOT add a ref if the policy at (vma,addr) is not

	 * marked as MPOL_SHARED. vma policies are protected by the mmap_sem.

	 * If no [shared/vma] mempolicy exists at the addr, get_policy() op

	 * must return NULL--i.e., do not "fallback" to task or system default

	 * policy.

	 */

	struct mempolicy *(*get_policy)(struct vm_area_struct *vma,

					unsigned long addr);

	int (*migrate)(struct vm_area_struct *vma, const nodemask_t *from,