memory_hotplug: handle empty zone when online_movable/online_kernel

Make online_movable/online_kernel can empty a zone or can move memory to a
empty zone.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -219,8 +219,17 @@ static void resize_zone(struct zone *zone, unsigned long start_pfn,
 {
 	zone_span_writelock(zone);
 
-	zone->zone_start_pfn = start_pfn;
-	zone->spanned_pages = end_pfn - start_pfn;
+	if (end_pfn - start_pfn) {
+		zone->zone_start_pfn = start_pfn;
+		zone->spanned_pages = end_pfn - start_pfn;
+	} else {
+		/*
+		 * make it consist as free_area_init_core(),
+		 * if spanned_pages = 0, then keep start_pfn = 0
+		 */
+		zone->zone_start_pfn = 0;
+		zone->spanned_pages = 0;
+	}
 
 	zone_span_writeunlock(zone);
 }
@@ -236,10 +245,19 @@ static void fix_zone_id(struct zone *zone, unsigned long start_pfn,
 		set_page_links(pfn_to_page(pfn), zid, nid, pfn);
 }
 
-static int move_pfn_range_left(struct zone *z1, struct zone *z2,
+static int __meminit move_pfn_range_left(struct zone *z1, struct zone *z2,
 		unsigned long start_pfn, unsigned long end_pfn)
 {
+	int ret;
 	unsigned long flags;
+	unsigned long z1_start_pfn;
+
+	if (!z1->wait_table) {
+		ret = init_currently_empty_zone(z1, start_pfn,
+			end_pfn - start_pfn, MEMMAP_HOTPLUG);
+		if (ret)
+			return ret;
+	}
 
 	pgdat_resize_lock(z1->zone_pgdat, &flags);
 
@@ -253,7 +271,13 @@ static int move_pfn_range_left(struct zone *z1, struct zone *z2,
 	if (end_pfn <= z2->zone_start_pfn)
 		goto out_fail;
 
-	resize_zone(z1, z1->zone_start_pfn, end_pfn);
+	/* use start_pfn for z1's start_pfn if z1 is empty */
+	if (z1->spanned_pages)
+		z1_start_pfn = z1->zone_start_pfn;
+	else
+		z1_start_pfn = start_pfn;
+
+	resize_zone(z1, z1_start_pfn, end_pfn);
 	resize_zone(z2, end_pfn, z2->zone_start_pfn + z2->spanned_pages);
 
 	pgdat_resize_unlock(z1->zone_pgdat, &flags);
@@ -266,10 +290,19 @@ out_fail:
 	return -1;
 }
 
-static int move_pfn_range_right(struct zone *z1, struct zone *z2,
+static int __meminit move_pfn_range_right(struct zone *z1, struct zone *z2,
 		unsigned long start_pfn, unsigned long end_pfn)
 {
+	int ret;
 	unsigned long flags;
+	unsigned long z2_end_pfn;
+
+	if (!z2->wait_table) {
+		ret = init_currently_empty_zone(z2, start_pfn,
+			end_pfn - start_pfn, MEMMAP_HOTPLUG);
+		if (ret)
+			return ret;
+	}
 
 	pgdat_resize_lock(z1->zone_pgdat, &flags);
 
@@ -283,8 +316,14 @@ static int move_pfn_range_right(struct zone *z1, struct zone *z2,
 	if (start_pfn >= z1->zone_start_pfn + z1->spanned_pages)
 		goto out_fail;
 
+	/* use end_pfn for z2's end_pfn if z2 is empty */
+	if (z2->spanned_pages)
+		z2_end_pfn = z2->zone_start_pfn + z2->spanned_pages;
+	else
+		z2_end_pfn = end_pfn;
+
 	resize_zone(z1, z1->zone_start_pfn, start_pfn);
-	resize_zone(z2, start_pfn, z2->zone_start_pfn + z2->spanned_pages);
+	resize_zone(z2, start_pfn, z2_end_pfn);
 
 	pgdat_resize_unlock(z1->zone_pgdat, &flags);