memory unplug: page offline

Logic.
 - set all pages in  [start,end)  as isolated migration-type.
   by this, all free pages in the range will be not-for-use.
 - Migrate all LRU pages in the range.
 - Test all pages in the range's refcnt is zero or not.

Todo:
 - allocate migration destination page from better area.
 - confirm page_count(page)== 0 && PageReserved(page) page is safe to be freed..
 (I don't like this kind of page but..
 - Find out pages which cannot be migrated.
 - more running tests.
 - Use reclaim for unplugging other memory type area.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a44715e82058..d315e1127dc9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4477,3 +4477,50 @@ void unset_migratetype_isolate(struct page *page)
 out:
 	spin_unlock_irqrestore(&zone->lock, 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;
+	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);
+		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--;
+		__mod_zone_page_state(zone, NR_FREE_PAGES,
+				      - (1UL << order));
+		for (i = 0; i < (1 << order); i++)
+			SetPageReserved((page+i));
+		pfn += (1 << order);
+	}
+	spin_unlock_irqrestore(&zone->lock, flags);
+}
+#endif