Linux Virtualization - Jun 2012 - [PATCH 0/4] make balloon pages movable by compaction

This patchset follows the main idea discussed at 2012 LSFMMS section:
"Ballooning for transparent huge pages" --
http://lwn.net/Articles/490114/

to introduce the required changes to the virtio_balloon driver, as well as
changes to the core compaction & migration bits, in order to allow
memory balloon pages become movable within a guest.

Rafael Aquini (4):
  mm: introduce compaction and migration for virtio ballooned pages
  virtio_balloon: handle concurrent accesses to virtio_balloon struct
    elements
  virtio_balloon: introduce migration primitives to balloon pages
  mm: add vm event counters for balloon pages compaction

 drivers/virtio/virtio_balloon.c |  142 +++++++++++++++++++++++++++++++++++----
 include/linux/mm.h              |   17 +++++
 include/linux/virtio_balloon.h  |    6 ++
 include/linux/vm_event_item.h   |    2 +
 mm/compaction.c                 |   74 ++++++++++++++++++++
 mm/migrate.c                    |   32 ++++++++-
 mm/vmstat.c                     |    4 ++
 7 files changed, 263 insertions(+), 14 deletions(-)


Preliminary test results:
(2 VCPU 1024mB RAM KVM guest running 3.5.0_rc4+)

* 64mB balloon:
[root at localhost ~]# awk '/compact/ {print}' /proc/vmstat
compact_blocks_moved 0
compact_pages_moved 0
compact_pagemigrate_failed 0
compact_stall 0
compact_fail 0
compact_success 0
compact_balloon_migrated 0
compact_balloon_failed 0
compact_balloon_isolated 0
compact_balloon_freed 0
[root at localhost ~]#
[root at localhost ~]# for i in $(seq 1 4); do echo 1>
/proc/sys/vm/compact_memory & done &>/dev/null
[1]   Done                    echo > /proc/sys/vm/compact_memory
[2]   Done                    echo > /proc/sys/vm/compact_memory
[3]-  Done                    echo > /proc/sys/vm/compact_memory
[4]+  Done                    echo > /proc/sys/vm/compact_memory
[root at localhost ~]#
[root at localhost ~]# awk '/compact/ {print}' /proc/vmstat
compact_blocks_moved 2683
compact_pages_moved 47502
compact_pagemigrate_failed 61
compact_stall 0
compact_fail 0
compact_success 0
compact_balloon_migrated 16384
compact_balloon_failed 0
compact_balloon_isolated 16384
compact_balloon_freed 16384


* 128mB balloon:
[root at localhost ~]# awk '/compact/ {print}' /proc/vmstat
compact_blocks_moved 0
compact_pages_moved 0
compact_pagemigrate_failed 0
compact_stall 0
compact_fail 0
compact_success 0
compact_balloon_migrated 0
compact_balloon_failed 0
compact_balloon_isolated 0
compact_balloon_freed 0
[root at localhost ~]#
[root at localhost ~]# for i in $(seq 1 4); do echo 1>
/proc/sys/vm/compact_memory & done &>/dev/null
[1]   Done                    echo > /proc/sys/vm/compact_memory
[2]   Done                    echo > /proc/sys/vm/compact_memory
[3]-  Done                    echo > /proc/sys/vm/compact_memory
[4]+  Done                    echo > /proc/sys/vm/compact_memory
[root at localhost ~]# awk '/compact/ {print}' /proc/vmstat
compact_blocks_moved 2624
compact_pages_moved 49195
compact_pagemigrate_failed 54
compact_stall 0
compact_fail 0
compact_success 0
compact_balloon_migrated 29350
compact_balloon_failed 29
compact_balloon_isolated 29379
compact_balloon_freed 29350
-- 
1.7.10.2

This patch introduces helper functions that teach compaction and migration bits
how to cope with pages which are part of a guest memory balloon, in order to
make them movable by memory compaction procedures.

Signed-off-by: Rafael Aquini <aquini at redhat.com>
---
 include/linux/mm.h |   17 +++++++++++++
 mm/compaction.c    |   72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/migrate.c       |   30 +++++++++++++++++++++-
 3 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b36d08c..360656e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1629,5 +1629,22 @@ static inline unsigned int debug_guardpage_minorder(void)
{ return 0; }
 static inline bool page_is_guard(struct page *page) { return false; }
 #endif /* CONFIG_DEBUG_PAGEALLOC */
 
+#if (defined(CONFIG_VIRTIO_BALLOON) || \
+	defined(CONFIG_VIRTIO_BALLOON_MODULE)) && defined(CONFIG_COMPACTION)
+extern int is_balloon_page(struct page *);
+extern int isolate_balloon_page(struct page *);
+extern int putback_balloon_page(struct page *);
+
+/* return 1 if page is part of a guest's memory balloon, 0 otherwise */
+static inline int PageBalloon(struct page *page)
+{
+	return is_balloon_page(page);
+}
+#else
+static inline int PageBalloon(struct page *page)		{ return 0; }
+static inline int isolate_balloon_page(struct page *page)	{ return 0; }
+static inline int putback_balloon_page(struct page *page)	{ return 0; }
+#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && COMPACTION */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */
diff --git a/mm/compaction.c b/mm/compaction.c
index 7ea259d..8835d55 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -14,6 +14,7 @@
 #include <linux/backing-dev.h>
 #include <linux/sysctl.h>
 #include <linux/sysfs.h>
+#include <linux/export.h>
 #include "internal.h"
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
@@ -312,6 +313,14 @@ isolate_migratepages_range(struct zone *zone, struct
compact_control *cc,
 			continue;
 		}
 
+		/*
+		 * For ballooned pages, we need to isolate them before testing
+		 * for PageLRU, as well as skip the LRU page isolation steps.
+		 */
+		if (PageBalloon(page))
+			if (isolate_balloon_page(page))
+				goto isolated_balloon_page;
+
 		if (!PageLRU(page))
 			continue;
 
@@ -338,6 +347,7 @@ isolate_migratepages_range(struct zone *zone, struct
compact_control *cc,
 
 		/* Successfully isolated */
 		del_page_from_lru_list(page, lruvec, page_lru(page));
+isolated_balloon_page:
 		list_add(&page->lru, migratelist);
 		cc->nr_migratepages++;
 		nr_isolated++;
@@ -903,4 +913,66 @@ void compaction_unregister_node(struct node *node)
 }
 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
 
+#if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)
+/*
+ * Balloon pages special page->mapping.
+ * users must properly allocate and initiliaze an instance of balloon_mapping,
+ * and set it as the page->mapping for balloon enlisted page instances.
+ *
+ * address_space_operations necessary methods for ballooned pages:
+ *   .migratepage    - used to perform balloon's page migration (as is)
+ *   .invalidatepage - used to isolate a page from balloon's page list
+ *   .freepage       - used to reinsert an isolated page to balloon's page
list
+ */
+struct address_space *balloon_mapping;
+EXPORT_SYMBOL(balloon_mapping);
+
+/* ballooned page id check */
+int is_balloon_page(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	if (mapping == balloon_mapping)
+		return 1;
+	return 0;
+}
+
+/* __isolate_lru_page() counterpart for a ballooned page */
+int isolate_balloon_page(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	if (mapping->a_ops->invalidatepage) {
+		/*
+		 * We can race against move_to_new_page() and stumble across a
+		 * locked 'newpage'. If we succeed on isolating it, the result
+		 * tends to be disastrous. So, we sanely skip PageLocked here.
+		 */
+		if (likely(!PageLocked(page) && get_page_unless_zero(page))) {
+			/*
+			 * A ballooned page, by default, has just one refcount.
+			 * Prevent concurrent compaction threads from isolating
+			 * an already isolated balloon page.
+			 */
+			if (page_count(page) == 2) {
+				mapping->a_ops->invalidatepage(page, 0);
+				return 1;
+			}
+			/* Drop refcount taken for this already isolated page */
+			put_page(page);
+		}
+	}
+	return 0;
+}
+
+/* putback_lru_page() counterpart for a ballooned page */
+int putback_balloon_page(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	if (mapping->a_ops->freepage) {
+		mapping->a_ops->freepage(page);
+		put_page(page);
+		return 1;
+	}
+	return 0;
+}
+#endif /* CONFIG_VIRTIO_BALLOON || CONFIG_VIRTIO_BALLOON_MODULE */
 #endif /* CONFIG_COMPACTION */
diff --git a/mm/migrate.c b/mm/migrate.c
index be26d5c..ffc02a4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -78,7 +78,10 @@ void putback_lru_pages(struct list_head *l)
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
-		putback_lru_page(page);
+		if (unlikely(PageBalloon(page)))
+			VM_BUG_ON(!putback_balloon_page(page));
+		else
+			putback_lru_page(page);
 	}
 }
 
@@ -783,6 +786,17 @@ static int __unmap_and_move(struct page *page, struct page
*newpage,
 		}
 	}
 
+	if (PageBalloon(page)) {
+		/*
+		 * A ballooned page does not need any special attention from
+		 * physical to virtual reverse mapping procedures.
+		 * To avoid burning cycles at rmap level,
+		 * skip attempts to unmap PTEs or remap swapcache.
+		 */
+		remap_swapcache = 0;
+		goto skip_unmap;
+	}
+
 	/*
 	 * Corner case handling:
 	 * 1. When a new swap-cache page is read into, it is added to the LRU
@@ -852,6 +866,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned
long private,
 			goto out;
 
 	rc = __unmap_and_move(page, newpage, force, offlining, mode);
+
+	if (PageBalloon(newpage)) {
+		/*
+		 * A ballooned page has been migrated already. Now, it is the
+		 * time to wrap-up counters, handle the old page back to Buddy
+		 * and return.
+		 */
+		list_del(&page->lru);
+		dec_zone_page_state(page, NR_ISOLATED_ANON +
+				    page_is_file_cache(page));
+		put_page(page);
+		__free_page(page);
+		return rc;
+	}
 out:
 	if (rc != -EAGAIN) {
 		/*
-- 
1.7.10.2

This patch introduces access sychronization to critical elements of struct
virtio_balloon, in order to allow the thread concurrency compaction/migration
bits might ended up imposing to the balloon driver on several situations.

Signed-off-by: Rafael Aquini <aquini at redhat.com>
---
 drivers/virtio/virtio_balloon.c |   45 +++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index bfbc15c..d47c5c2 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -51,6 +51,10 @@ struct virtio_balloon
 
 	/* Number of balloon pages we've told the Host we're not using. */
 	unsigned int num_pages;
+
+	/* Protect 'pages', 'pfns' & 'num_pnfs' against
concurrent updates */
+	spinlock_t pfn_list_lock;
+
 	/*
 	 * The pages we've told the Host we're not using.
 	 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
@@ -97,21 +101,23 @@ static void balloon_ack(struct virtqueue *vq)
 		complete(&vb->acked);
 }
 
-static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
-{
-	struct scatterlist sg;
-
-	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+/* Protection for concurrent accesses to balloon virtqueues and vb->acked */
+DEFINE_MUTEX(vb_queue_completion);
 
+static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq,
+		      struct scatterlist *sg)
+{
+	mutex_lock(&vb_queue_completion);
 	init_completion(&vb->acked);
 
 	/* We should always be able to add one buffer to an empty queue. */
-	if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
+	if (virtqueue_add_buf(vq, sg, 1, 0, vb, GFP_KERNEL) < 0)
 		BUG();
 	virtqueue_kick(vq);
 
 	/* When host has read buffer, this completes via balloon_ack */
 	wait_for_completion(&vb->acked);
+	mutex_unlock(&vb_queue_completion);
 }
 
 static void set_page_pfns(u32 pfns[], struct page *page)
@@ -126,9 +132,12 @@ static void set_page_pfns(u32 pfns[], struct page *page)
 
 static void fill_balloon(struct virtio_balloon *vb, size_t num)
 {
+	struct scatterlist sg;
+	int alloc_failed = 0;
 	/* We can only do one array worth at a time. */
 	num = min(num, ARRAY_SIZE(vb->pfns));
 
+	spin_lock(&vb->pfn_list_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
@@ -138,8 +147,7 @@ static void fill_balloon(struct virtio_balloon *vb, size_t
num)
 				dev_printk(KERN_INFO, &vb->vdev->dev,
 					   "Out of puff! Can't get %zu pages\n",
 					   num);
-			/* Sleep for at least 1/5 of a second before retry. */
-			msleep(200);
+			alloc_failed = 1;
 			break;
 		}
 		set_page_pfns(vb->pfns + vb->num_pfns, page);
@@ -149,10 +157,19 @@ static void fill_balloon(struct virtio_balloon *vb, size_t
num)
 	}
 
 	/* Didn't get any?  Oh well. */
-	if (vb->num_pfns == 0)
+	if (vb->num_pfns == 0) {
+		spin_unlock(&vb->pfn_list_lock);
 		return;
+	}
+
+	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+	spin_unlock(&vb->pfn_list_lock);
 
-	tell_host(vb, vb->inflate_vq);
+	/* alloc_page failed, sleep for at least 1/5 of a sec before retry. */
+	if (alloc_failed)
+		msleep(200);
+
+	tell_host(vb, vb->inflate_vq, &sg);
 }
 
 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
@@ -169,10 +186,12 @@ static void release_pages_by_pfn(const u32 pfns[],
unsigned int num)
 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 {
 	struct page *page;
+	struct scatterlist sg;
 
 	/* We can only do one array worth at a time. */
 	num = min(num, ARRAY_SIZE(vb->pfns));
 
+	spin_lock(&vb->pfn_list_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		page = list_first_entry(&vb->pages, struct page, lru);
@@ -180,13 +199,15 @@ static void leak_balloon(struct virtio_balloon *vb, size_t
num)
 		set_page_pfns(vb->pfns + vb->num_pfns, page);
 		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 	}
+	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+	spin_unlock(&vb->pfn_list_lock);
 
 	/*
 	 * Note that if
 	 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 	 * is true, we *have* to do it in this order
 	 */
-	tell_host(vb, vb->deflate_vq);
+	tell_host(vb, vb->deflate_vq, &sg);
 	release_pages_by_pfn(vb->pfns, vb->num_pfns);
 }
 
@@ -356,6 +377,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	}
 
 	INIT_LIST_HEAD(&vb->pages);
+	spin_lock_init(&vb->pfn_list_lock);
+
 	vb->num_pages = 0;
 	init_waitqueue_head(&vb->config_change);
 	vb->vdev = vdev;
-- 
1.7.10.2

This patch makes balloon pages movable at allocation time and introduces the
infrastructure needed to perform the balloon page migration operation.

Signed-off-by: Rafael Aquini <aquini at redhat.com>
---
 drivers/virtio/virtio_balloon.c |   96 ++++++++++++++++++++++++++++++++++++++-
 include/linux/virtio_balloon.h  |    6 +++
 2 files changed, 100 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index d47c5c2..53386aa 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -27,6 +27,8 @@
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -140,8 +142,9 @@ static void fill_balloon(struct virtio_balloon *vb, size_t
num)
 	spin_lock(&vb->pfn_list_lock);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
-		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
-					__GFP_NOMEMALLOC | __GFP_NOWARN);
+		struct page *page = alloc_page(GFP_HIGHUSER_MOVABLE |
+						__GFP_NORETRY | __GFP_NOWARN |
+						__GFP_NOMEMALLOC);
 		if (!page) {
 			if (printk_ratelimit())
 				dev_printk(KERN_INFO, &vb->vdev->dev,
@@ -154,6 +157,7 @@ static void fill_balloon(struct virtio_balloon *vb, size_t
num)
 		vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 		totalram_pages--;
 		list_add(&page->lru, &vb->pages);
+		page->mapping = balloon_mapping;
 	}
 
 	/* Didn't get any?  Oh well. */
@@ -195,6 +199,7 @@ static void leak_balloon(struct virtio_balloon *vb, size_t
num)
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		page = list_first_entry(&vb->pages, struct page, lru);
+		page->mapping = NULL;
 		list_del(&page->lru);
 		set_page_pfns(vb->pfns + vb->num_pfns, page);
 		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
@@ -365,6 +370,77 @@ static int init_vqs(struct virtio_balloon *vb)
 	return 0;
 }
 
+/*
+ * Populate balloon_mapping->a_ops->migratepage method to perform the
balloon
+ * page migration task.
+ *
+ * After a ballooned page gets isolated by compaction procedures, this is the
+ * function that performs the page migration on behalf of move_to_new_page(),
+ * when the last calls (page)->mapping->a_ops->migratepage.
+ *
+ * Page migration for virtio balloon is done in a simple swap fashion which
+ * follows these two steps:
+ *  1) insert newpage into vb->pages list and update the host about it;
+ *  2) update the host about the removed old page from vb->pages list;
+ */
+int virtballoon_migratepage(struct address_space *mapping,
+		struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+	struct virtio_balloon *vb = (void *)mapping->backing_dev_info;
+	struct scatterlist sg;
+
+	/* balloon's page migration 1st step */
+	spin_lock(&vb->pfn_list_lock);
+	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
+	list_add(&newpage->lru, &vb->pages);
+	set_page_pfns(vb->pfns, newpage);
+	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+	spin_unlock(&vb->pfn_list_lock);
+	tell_host(vb, vb->inflate_vq, &sg);
+
+	/* balloon's page migration 2nd step */
+	spin_lock(&vb->pfn_list_lock);
+	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
+	set_page_pfns(vb->pfns, page);
+	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+	spin_unlock(&vb->pfn_list_lock);
+	tell_host(vb, vb->deflate_vq, &sg);
+
+	return 0;
+}
+
+/*
+ * Populate balloon_mapping->a_ops->invalidatepage method to help
compaction on
+ * isolating a page from the balloon page list.
+ */
+void virtballoon_isolatepage(struct page *page, unsigned long mode)
+{
+	struct address_space *mapping = page->mapping;
+	struct virtio_balloon *vb = (void *)mapping->backing_dev_info;
+	spin_lock(&vb->pfn_list_lock);
+	list_del(&page->lru);
+	spin_unlock(&vb->pfn_list_lock);
+}
+
+/*
+ * Populate balloon_mapping->a_ops->freepage method to help compaction on
+ * re-inserting an isolated page into the balloon page list.
+ */
+void virtballoon_putbackpage(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	struct virtio_balloon *vb = (void *)mapping->backing_dev_info;
+	spin_lock(&vb->pfn_list_lock);
+	list_add(&page->lru, &vb->pages);
+	spin_unlock(&vb->pfn_list_lock);
+}
+
+static const struct address_space_operations virtio_balloon_aops = {
+	.migratepage = virtballoon_migratepage,
+	.invalidatepage = virtballoon_isolatepage,
+	.freepage = virtballoon_putbackpage,
+};
+
 static int virtballoon_probe(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb;
@@ -384,6 +460,19 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	vb->vdev = vdev;
 	vb->need_stats_update = 0;
 
+	/* Init the ballooned page->mapping special balloon_mapping */
+	balloon_mapping = kmalloc(sizeof(*balloon_mapping), GFP_KERNEL);
+	if (!balloon_mapping) {
+		err = -ENOMEM;
+		goto out_free_mapping;
+	}
+
+	INIT_RADIX_TREE(&balloon_mapping->page_tree, GFP_ATOMIC |
__GFP_NOWARN);
+	INIT_LIST_HEAD(&balloon_mapping->i_mmap_nonlinear);
+	spin_lock_init(&balloon_mapping->tree_lock);
+	balloon_mapping->a_ops = &virtio_balloon_aops;
+	balloon_mapping->backing_dev_info = (void *)vb;
+
 	err = init_vqs(vb);
 	if (err)
 		goto out_free_vb;
@@ -398,6 +487,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
 
 out_del_vqs:
 	vdev->config->del_vqs(vdev);
+out_free_mapping:
+	kfree(balloon_mapping);
 out_free_vb:
 	kfree(vb);
 out:
@@ -424,6 +515,7 @@ static void __devexit virtballoon_remove(struct
virtio_device *vdev)
 	kthread_stop(vb->thread);
 	remove_common(vb);
 	kfree(vb);
+	kfree(balloon_mapping);
 }
 
 #ifdef CONFIG_PM
diff --git a/include/linux/virtio_balloon.h b/include/linux/virtio_balloon.h
index 652dc8b..db21300 100644
--- a/include/linux/virtio_balloon.h
+++ b/include/linux/virtio_balloon.h
@@ -56,4 +56,10 @@ struct virtio_balloon_stat {
 	u64 val;
 } __attribute__((packed));
 
+#if defined(CONFIG_COMPACTION)
+extern struct address_space *balloon_mapping;
+#else
+struct address_space *balloon_mapping;
+#endif
+
 #endif /* _LINUX_VIRTIO_BALLOON_H */
-- 
1.7.10.2

This patch is only for testing report purposes and shall be dropped in case of
the rest of this patchset getting accepted for merging.

Signed-off-by: Rafael Aquini <aquini at redhat.com>
---
 drivers/virtio/virtio_balloon.c |    1 +
 include/linux/vm_event_item.h   |    2 ++
 mm/compaction.c                 |    4 +++-
 mm/migrate.c                    |    6 ++++--
 mm/vmstat.c                     |    4 ++++
 5 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 53386aa..c4a929d 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -406,6 +406,7 @@ int virtballoon_migratepage(struct address_space *mapping,
 	spin_unlock(&vb->pfn_list_lock);
 	tell_host(vb, vb->deflate_vq, &sg);
 
+	count_vm_event(COMPACTBALLOONMIGRATED);
 	return 0;
 }
 
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 06f8e38..e330c5a 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -40,6 +40,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_COMPACTION
 		COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
 		COMPACTSTALL, COMPACTFAIL, COMPACTSUCCESS,
+		COMPACTBALLOONMIGRATED, COMPACTBALLOONFAILED,
+		COMPACTBALLOONISOLATED, COMPACTBALLOONFREED,
 #endif
 #ifdef CONFIG_HUGETLB_PAGE
 		HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
diff --git a/mm/compaction.c b/mm/compaction.c
index 8835d55..cf250b8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -318,8 +318,10 @@ isolate_migratepages_range(struct zone *zone, struct
compact_control *cc,
 		 * for PageLRU, as well as skip the LRU page isolation steps.
 		 */
 		if (PageBalloon(page))
-			if (isolate_balloon_page(page))
+			if (isolate_balloon_page(page)) {
+				count_vm_event(COMPACTBALLOONISOLATED);
 				goto isolated_balloon_page;
+		}
 
 		if (!PageLRU(page))
 			continue;
diff --git a/mm/migrate.c b/mm/migrate.c
index ffc02a4..3dbca33 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -78,9 +78,10 @@ void putback_lru_pages(struct list_head *l)
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
-		if (unlikely(PageBalloon(page)))
+		if (unlikely(PageBalloon(page))) {
 			VM_BUG_ON(!putback_balloon_page(page));
-		else
+			count_vm_event(COMPACTBALLOONFAILED);
+		} else
 			putback_lru_page(page);
 	}
 }
@@ -878,6 +879,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned
long private,
 				    page_is_file_cache(page));
 		put_page(page);
 		__free_page(page);
+		count_vm_event(COMPACTBALLOONFREED);
 		return rc;
 	}
 out:
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1bbbbd9..3b7109f 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -767,6 +767,10 @@ const char * const vmstat_text[] = {
 	"compact_stall",
 	"compact_fail",
 	"compact_success",
+	"compact_balloon_migrated",
+	"compact_balloon_failed",
+	"compact_balloon_isolated",
+	"compact_balloon_freed",
 #endif
 
 #ifdef CONFIG_HUGETLB_PAGE
-- 
1.7.10.2

On 06/25/2012 07:25 PM, Rafael Aquini wrote:
> This patch introduces helper functions that teach compaction and migration
bits
> how to cope with pages which are part of a guest memory balloon, in order
to
> make them movable by memory compaction procedures.
>
> Signed-off-by: Rafael Aquini<aquini at redhat.com>
The function fill_balloon in drivers/virtio/virtio_balloon.c
should probably add __GFP_MOVABLE to the gfp mask for alloc_pages,
to keep the pageblock where balloon pages are allocated marked
as movable.

-- 
All rights reversed