mm/page_alloc: insert memory barriers to allow async update of pcp batch and high

#endif

}

/*

 * 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.

 *

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

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

 *

 * mutex_is_locked(&pcp_batch_high_lock) required when calling this function

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

 * exist).

 */

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;

}

/* a companion to setup_pagelist_highmark() */

static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)

{

	struct per_cpu_pages *pcp = &p->pcp;

	pcp->high = 6 * batch;

	pcp->batch = max(1UL, 1 * batch);

	pageset_update(&p->pcp, 6 * batch, max(1UL, 1 * batch));

}

static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)

static void setup_pagelist_highmark(struct per_cpu_pageset *p,

				unsigned long high)

{

	struct per_cpu_pages *pcp;

	pcp = &p->pcp;

	pcp->high = high;

	pcp->batch = max(1UL, high/4);

	unsigned long batch = max(1UL, high / 4);

	if ((high / 4) > (PAGE_SHIFT * 8))

		pcp->batch = PAGE_SHIFT * 8;

		batch = PAGE_SHIFT * 8;

	pageset_update(&p->pcp, high, batch);

}

static void __meminit setup_zone_pageset(struct zone *zone)