mm, page_alloc: simplify pageset_update()

{

	int migratetype = 0;

	int batch_free = 0;

	int prefetch_nr = 0;

	int prefetch_nr = READ_ONCE(pcp->batch);

	bool isolated_pageblocks;

	struct page *page, *tmp;

	LIST_HEAD(head);

			 * avoid excessive prefetching due to large count, only

			 * prefetch buddy for the first pcp->batch nr of pages.

			 */

			if (prefetch_nr++ < pcp->batch)

			if (prefetch_nr) {

				prefetch_buddy(page);

				prefetch_nr--;

			}

		} while (--count && --batch_free && !list_empty(list));

	}

	pcp = &this_cpu_ptr(zone->pageset)->pcp;

	list_add(&page->lru, &pcp->lists[migratetype]);

	pcp->count++;

	if (pcp->count >= pcp->high) {

		unsigned long batch = READ_ONCE(pcp->batch);

		free_pcppages_bulk(zone, batch, pcp);

	}

	if (pcp->count >= READ_ONCE(pcp->high))

		free_pcppages_bulk(zone, READ_ONCE(pcp->batch), pcp);

}

/*

	do {

		if (list_empty(list)) {

			pcp->count += rmqueue_bulk(zone, 0,

					pcp->batch, list,

					READ_ONCE(pcp->batch), list,

					migratetype, alloc_flags);

			if (unlikely(list_empty(list)))

				return NULL;

}

/*

 * pcp->high and pcp->batch values are related and dependent on one another:

 * ->batch must never be higher then ->high.

 * The following function updates them in a safe manner without read side

 * locking.

 * pcp->high and pcp->batch values are related and generally batch is lower

 * than high. They are also related to pcp->count such that count is lower

 * than high, and as soon as it reaches high, the pcplist is flushed.

 *

 * Any new users of pcp->batch and pcp->high should ensure they can cope with

 * those fields changing asynchronously (acording to the above rule).

 * However, guaranteeing these relations at all times would require e.g. write

 * barriers here but also careful usage of read barriers at the read side, and

 * thus be prone to error and bad for performance. Thus the update only prevents

 * store tearing. Any new users of pcp->batch and pcp->high should ensure they

 * can cope with those fields changing asynchronously, and fully trust only the

 * pcp->count field on the local CPU with interrupts disabled.

 *

 * mutex_is_locked(&pcp_batch_high_lock) required when calling this function

 * outside of boot time (or some other assurance that no concurrent updaters

static void pageset_update(struct per_cpu_pages *pcp, unsigned long high,

		unsigned long batch)

{

       /* start with a fail safe value for batch */

	pcp->batch = 1;

	smp_wmb();

       /* Update high, then batch, in order */

	pcp->high = high;

	smp_wmb();

	pcp->batch = batch;

	WRITE_ONCE(pcp->batch, batch);

	WRITE_ONCE(pcp->high, high);

}

static void pageset_init(struct per_cpu_pageset *p)