page_alloc.c

	 * we are interested in).  This will put all the pages in
	 * range back to page allocator as MIGRATE_ISOLATE.
	 *
	 * When this is done, we take the pages in range from page
	 * allocator removing them from the buddy system.  This way
	 * page allocator will never consider using them.
	 *
	 * This lets us mark the pageblocks back as
	 * MIGRATE_CMA/MIGRATE_MOVABLE so that free pages in the
	 * aligned range but not in the unaligned, original range are
	 * put back to page allocator so that buddy can use them.
	 */

	ret = start_isolate_page_range(pfn_max_align_down(start),
				       pfn_max_align_up(end), migratetype,
				       false);
	if (ret)
		return ret;

	/*
	 * In case of -EBUSY, we'd like to know which page causes problem.
	 * So, just fall through. We will check it in test_pages_isolated().
	 */
	ret = __alloc_contig_migrate_range(&cc, start, end);
	if (ret && ret != -EBUSY)
		goto done;

	/*
	 * Pages from [start, end) are within a MAX_ORDER_NR_PAGES
	 * aligned blocks that are marked as MIGRATE_ISOLATE.  What's
	 * more, all pages in [start, end) are free in page allocator.
	 * What we are going to do is to allocate all pages from
	 * [start, end) (that is remove them from page allocator).
	 *
	 * The only problem is that pages at the beginning and at the
	 * end of interesting range may be not aligned with pages that
	 * page allocator holds, ie. they can be part of higher order
	 * pages.  Because of this, we reserve the bigger range and
	 * once this is done free the pages we are not interested in.
	 *
	 * We don't have to hold zone->lock here because the pages are
	 * isolated thus they won't get removed from buddy.
	 */

	lru_add_drain_all();
	drain_all_pages(cc.zone);

	order = 0;
	outer_start = start;
	while (!PageBuddy(pfn_to_page(outer_start))) {
		if (++order >= MAX_ORDER) {
			outer_start = start;
			break;
		}
		outer_start &= ~0UL << order;
	}

	if (outer_start != start) {
		order = page_order(pfn_to_page(outer_start));

		/*
		 * outer_start page could be small order buddy page and
		 * it doesn't include start page. Adjust outer_start
		 * in this case to report failed page properly
		 * on tracepoint in test_pages_isolated()
		 */
		if (outer_start + (1UL << order) <= start)
			outer_start = start;
	}

	/* Make sure the range is really isolated. */
	if (test_pages_isolated(outer_start, end, false)) {
		pr_info("%s: [%lx, %lx) PFNs busy\n",
			__func__, outer_start, end);
		ret = -EBUSY;
		goto done;
	}

	/* Grab isolated pages from freelists. */
	outer_end = isolate_freepages_range(&cc, outer_start, end);
	if (!outer_end) {
		ret = -EBUSY;
		goto done;
	}

	/* Free head and tail (if any) */
	if (start != outer_start)
		free_contig_range(outer_start, start - outer_start);
	if (end != outer_end)
		free_contig_range(end, outer_end - end);

done:
	undo_isolate_page_range(pfn_max_align_down(start),
				pfn_max_align_up(end), migratetype);
	return ret;
}

void free_contig_range(unsigned long pfn, unsigned nr_pages)
{
	unsigned int count = 0;

	for (; nr_pages--; pfn++) {
		struct page *page = pfn_to_page(pfn);

		count += page_count(page) != 1;
		__free_page(page);
	}
	WARN(count != 0, "%d pages are still in use!\n", count);
}
#endif

#ifdef CONFIG_MEMORY_HOTPLUG
/*
 * The zone indicated has a new number of managed_pages; batch sizes and percpu
 * page high values need to be recalulated.
 */
void __meminit zone_pcp_update(struct zone *zone)
{
	unsigned cpu;
	mutex_lock(&pcp_batch_high_lock);
	for_each_possible_cpu(cpu)
		pageset_set_high_and_batch(zone,
				per_cpu_ptr(zone->pageset, cpu));
	mutex_unlock(&pcp_batch_high_lock);
}
#endif

void zone_pcp_reset(struct zone *zone)
{
	unsigned long flags;
	int cpu;
	struct per_cpu_pageset *pset;

	/* avoid races with drain_pages()  */
	local_irq_save(flags);
	if (zone->pageset != &boot_pageset) {
		for_each_online_cpu(cpu) {
			pset = per_cpu_ptr(zone->pageset, cpu);
			drain_zonestat(zone, pset);
		}
		free_percpu(zone->pageset);
		zone->pageset = &boot_pageset;
	}
	local_irq_restore(flags);
}

#ifdef CONFIG_MEMORY_HOTREMOVE
/*
 * All pages in the range must be isolated before calling this.
 */
void
__offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
{
	struct page *page;
	struct zone *zone;
	unsigned int order, i;
	unsigned long pfn;
	unsigned long flags;
	/* find the first valid pfn */
	for (pfn = start_pfn; pfn < end_pfn; pfn++)
		if (pfn_valid(pfn))
			break;
	if (pfn == end_pfn)
		return;
	zone = page_zone(pfn_to_page(pfn));
	spin_lock_irqsave(&zone->lock, flags);
	pfn = start_pfn;
	while (pfn < end_pfn) {
		if (!pfn_valid(pfn)) {
			pfn++;
			continue;
		}
		page = pfn_to_page(pfn);
		/*
		 * The HWPoisoned page may be not in buddy system, and
		 * page_count() is not 0.
		 */
		if (unlikely(!PageBuddy(page) && PageHWPoison(page))) {
			pfn++;
			SetPageReserved(page);
			continue;
		}

		BUG_ON(page_count(page));
		BUG_ON(!PageBuddy(page));
		order = page_order(page);
#ifdef CONFIG_DEBUG_VM
		printk(KERN_INFO "remove from free list %lx %d %lx\n",
		       pfn, 1 << order, end_pfn);
#endif
		list_del(&page->lru);
		rmv_page_order(page);
		zone->free_area[order].nr_free--;
		for (i = 0; i < (1 << order); i++)
			SetPageReserved((page+i));
		pfn += (1 << order);
	}
	spin_unlock_irqrestore(&zone->lock, flags);
}
#endif

bool is_free_buddy_page(struct page *page)
{
	struct zone *zone = page_zone(page);
	unsigned long pfn = page_to_pfn(page);
	unsigned long flags;
	unsigned int order;

	spin_lock_irqsave(&zone->lock, flags);
	for (order = 0; order < MAX_ORDER; order++) {
		struct page *page_head = page - (pfn & ((1 << order) - 1));

		if (PageBuddy(page_head) && page_order(page_head) >= order)
			break;
	}
	spin_unlock_irqrestore(&zone->lock, flags);

	return order < MAX_ORDER;
}