mm/mempolicy: rewrite alloc_pages_vma documentation

/**

 * alloc_pages_vma - Allocate a page for a VMA.

 *

 * 	@gfp:

 *      %GFP_USER    user allocation.

 *      %GFP_KERNEL  kernel allocations,

 *      %GFP_HIGHMEM highmem/user allocations,

 *      %GFP_FS      allocation should not call back into a file system.

 *      %GFP_ATOMIC  don't sleep.

 *

 * @gfp: GFP flags.

 * @order: Order of the GFP allocation.

 * @vma: Pointer to VMA or NULL if not available.

 *	@addr: Virtual Address of the allocation. Must be inside the VMA.

 * @addr: Virtual address of the allocation.  Must be inside @vma.

 * @node: Which node to prefer for allocation (modulo policy).

 *	@hugepage: for hugepages try only the preferred node if possible

 * @hugepage: For hugepages try only the preferred node if possible.

 *

 * 	This function allocates a page from the kernel page pool and applies

 *	a NUMA policy associated with the VMA or the current process.

 *	When VMA is not NULL caller must read-lock the mmap_lock of the

 *	mm_struct of the VMA to prevent it from going away. Should be used for

 *	all allocations for pages that will be mapped into user space. Returns

 *	NULL when no page can be allocated.

 */

struct page *

alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,

 * Allocate a page for a specific address in @vma, using the appropriate

 * NUMA policy.  When @vma is not NULL the caller must hold the mmap_lock

 * of the mm_struct of the VMA to prevent it from going away.  Should be

 * used for all allocations for pages that will be mapped into user space.

 *

 * Return: The page on success or NULL if allocation fails.

 */

struct page *alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,

		unsigned long addr, int node, bool hugepage)

{

	struct mempolicy *pol;