diff -up ./drivers/hv/hv_balloon.c.ha00 ./drivers/hv/hv_balloon.c
--- ./drivers/hv/hv_balloon.c.ha00	2020-02-12 18:58:25.000000000 +0900
+++ ./drivers/hv/hv_balloon.c	2020-02-17 09:19:27.047752736 +0900
@@ -730,8 +730,10 @@ static void hv_mem_hot_add(unsigned long
 		dm_device.ha_waiting = !memhp_auto_online;
 
 		nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
+pr_info("%s: calling add_memory(nid=%d, ((start_pfn=0x%lx) << PAGE_SHIFT)=0x%llx, (HA_CHUNK << PAGE_SHIFT)=%lu)\n", __func__, nid, start_pfn, ((unsigned long long)start_pfn << PAGE_SHIFT), (HA_CHUNK << PAGE_SHIFT));
 		ret = add_memory(nid, PFN_PHYS((start_pfn)),
 				(HA_CHUNK << PAGE_SHIFT));
+pr_info("%s: add_memory() returned %d\n", __func__, ret);
 
 		if (ret) {
 			pr_err("hot_add memory failed error is %d\n", ret);
diff -up ./mm/memory_hotplug.c.ha00 ./mm/memory_hotplug.c
--- ./mm/memory_hotplug.c.ha00	2020-02-12 18:59:43.000000000 +0900
+++ ./mm/memory_hotplug.c	2020-02-17 20:33:07.246405401 +0900
@@ -574,6 +574,7 @@ EXPORT_SYMBOL_GPL(restore_online_page_ca
 
 void generic_online_page(struct page *page, unsigned int order)
 {
+//pr_info("%s: called as (page=0x%px order=%u)\n", __func__, page, order); /*2b9c821d*/
 	kernel_map_pages(page, 1 << order, 1);
 	__free_pages_core(page, order);
 	totalram_pages_add(1UL << order);
@@ -711,15 +712,19 @@ static struct zone *default_kernel_zone_
 {
 	struct pglist_data *pgdat = NODE_DATA(nid);
 	int zid;
+	enum  zone_type default_zone = ZONE_NORMAL; /*9faf47bd*/
 
-	for (zid = 0; zid <= ZONE_NORMAL; zid++) {
+#ifdef CONFIG_HIGHMEM				/*9faf47bd*/
+	default_zone = ZONE_HIGHMEM;		/*9faf47bd*/
+#endif						/*9faf47bd*/
+	for (zid = 0; zid <= default_zone; zid++) { /*9faf47bd*/
 		struct zone *zone = &pgdat->node_zones[zid];
 
 		if (zone_intersects(zone, start_pfn, nr_pages))
 			return zone;
 	}
 
-	return &pgdat->node_zones[ZONE_NORMAL];
+	return &pgdat->node_zones[default_zone]; /*9faf47bd*/
 }
 
 static inline struct zone *default_zone_for_pfn(int nid, unsigned long start_pfn,
@@ -774,6 +779,7 @@ int __ref online_pages(unsigned long pfn
 	zone = zone_for_pfn_range(online_type, nid, pfn, nr_pages);
 	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL);
 
+pr_info("%s: pfn: %lx - %lx (zone: %s)\n", __func__, pfn, pfn + nr_pages, zone->name); /*2b9c821d*/
 	arg.start_pfn = pfn;
 	arg.nr_pages = nr_pages;
 	node_states_check_changes_online(nr_pages, zone, &arg);
diff -up ./mm/sparse.c.ha00 ./mm/sparse.c
--- ./mm/sparse.c.ha00	2020-02-17 09:19:27.029752732 +0900
+++ ./mm/sparse.c	2020-02-17 16:41:45.775823324 +0900
@@ -664,22 +664,29 @@ static void free_map_bootmem(struct page
 struct page * __meminit populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
 {
-	struct page *page, *ret;
+	struct page * volatile page, *ret;
 	unsigned long memmap_size = sizeof(struct page) * PAGES_PER_SECTION;
 
 	page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
-	if (page)
+	if (page) {
 		goto got_map_page;
+	}
+pr_info("%s: alloc_pages() returned 0x%p (should be 0), reverting to vmalloc(memmap_size=%lu)\n", __func__, page, memmap_size);
+BUG_ON(page != 0);
 
 	ret = vmalloc(memmap_size);
-	if (ret)
+pr_info("%s: vmalloc(%lu) returned 0x%p\n", __func__, memmap_size, ret);
+	if (ret) {
 		goto got_map_ptr;
+	}
 
 	return NULL;
 got_map_page:
 	ret = (struct page *)pfn_to_kaddr(page_to_pfn(page));
+pr_info("%s: allocated struct page *page=0x%p\n", __func__, page);
 got_map_ptr:
 
+pr_info("%s: returning struct page * =0x%p\n", __func__, ret);
 	return ret;
 }