mm/balloon_compaction: add vmstat counters and kpageflags bit

Always mark pages with PageBalloon even if balloon compaction is disabled
and expose this mark in /proc/kpageflags as KPF_BALLOON.

Also this patch adds three counters into /proc/vmstat: "balloon_inflate",
"balloon_deflate" and "balloon_migrate".  They accumulate balloon
activity.  Current size of balloon is (balloon_inflate - balloon_deflate)
pages.

All generic balloon code now gathered under option CONFIG_MEMORY_BALLOON.
It should be selected by ballooning driver which wants use this feature.
Currently virtio-balloon is the only user.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/Kconfig b/mm/Kconfig
index 0ceb8a5..1d1ae6b 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -231,11 +231,16 @@
 	boolean
 
 #
+# support for memory balloon
+config MEMORY_BALLOON
+	boolean
+
+#
 # support for memory balloon compaction
 config BALLOON_COMPACTION
 	bool "Allow for balloon memory compaction/migration"
 	def_bool y
-	depends on COMPACTION && VIRTIO_BALLOON
+	depends on COMPACTION && MEMORY_BALLOON
 	help
 	  Memory fragmentation introduced by ballooning might reduce
 	  significantly the number of 2MB contiguous memory blocks that can be
diff --git a/mm/Makefile b/mm/Makefile
index f8ed7ab..1f534a7 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -16,7 +16,7 @@
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   util.o mmzone.o vmstat.o backing-dev.o \
 			   mm_init.o mmu_context.o percpu.o slab_common.o \
-			   compaction.o balloon_compaction.o vmacache.o \
+			   compaction.o vmacache.o \
 			   interval_tree.o list_lru.o workingset.o \
 			   iov_iter.o debug.o $(mmu-y)
 
@@ -67,3 +67,4 @@
 obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o
 obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
 obj-$(CONFIG_CMA)	+= cma.o
+obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 3afdabd..b3cbe19 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -36,6 +36,7 @@
 	BUG_ON(!trylock_page(page));
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	balloon_page_insert(b_dev_info, page);
+	__count_vm_event(BALLOON_INFLATE);
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 	unlock_page(page);
 	return page;
@@ -74,6 +75,7 @@
 			}
 			spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 			balloon_page_delete(page);
+			__count_vm_event(BALLOON_DEFLATE);
 			spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 			unlock_page(page);
 			dequeued_page = true;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index e9ab104..cce7c76 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -735,7 +735,7 @@
 					TEXT_FOR_HIGHMEM(xx) xx "_movable",
 
 const char * const vmstat_text[] = {
-	/* Zoned VM counters */
+	/* enum zone_stat_item countes */
 	"nr_free_pages",
 	"nr_alloc_batch",
 	"nr_inactive_anon",
@@ -778,10 +778,13 @@
 	"workingset_nodereclaim",
 	"nr_anon_transparent_hugepages",
 	"nr_free_cma",
+
+	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",
 	"nr_dirty_background_threshold",
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
+	/* enum vm_event_item counters */
 	"pgpgin",
 	"pgpgout",
 	"pswpin",
@@ -860,6 +863,13 @@
 	"thp_zero_page_alloc",
 	"thp_zero_page_alloc_failed",
 #endif
+#ifdef CONFIG_MEMORY_BALLOON
+	"balloon_inflate",
+	"balloon_deflate",
+#ifdef CONFIG_BALLOON_COMPACTION
+	"balloon_migrate",
+#endif
+#endif /* CONFIG_MEMORY_BALLOON */
 #ifdef CONFIG_DEBUG_TLBFLUSH
 #ifdef CONFIG_SMP
 	"nr_tlb_remote_flush",