docs/mm: bootmem: add kernel-doc description of 'struct bootmem_data'

extern unsigned long long max_possible_pfn;

#ifndef CONFIG_NO_BOOTMEM

/*

 * node_bootmem_map is a map pointer - the bits represent all physical 

/**

 * struct bootmem_data - per-node information used by the bootmem allocator

 * @node_min_pfn: the starting physical address of the node's memory

 * @node_low_pfn: the end physical address of the directly addressable memory

 * @node_bootmem_map: is a bitmap pointer - the bits represent all physical

 *		      memory pages (including holes) on the node.

 * @last_end_off: the offset within the page of the end of the last allocation;

 *                if 0, the page used is full

 * @hint_idx: the PFN of the page used with the last allocation;

 *            together with using this with the @last_end_offset field,

 *            a test can be made to see if allocations can be merged

 *            with the page used for the last allocation rather than

 *            using up a full new page.

 * @list: list entry in the linked list ordered by the memory addresses

 */

typedef struct bootmem_data {

	unsigned long node_min_pfn;