6 files changed, 617 insertions, 1 deletions

diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
new file mode 100644
index 000000000000..f7f1d7169b11
--- /dev/null
+++ b/include/linux/balloon_compaction.h
@@ -0,0 +1,272 @@
+/*
+ * include/linux/balloon_compaction.h
+ *
+ * Common interface definitions for making balloon pages movable by compaction.
+ *
+ * Despite being perfectly possible to perform ballooned pages migration, they
+ * make a special corner case to compaction scans because balloon pages are not
+ * enlisted at any LRU list like the other pages we do compact / migrate.
+ *
+ * As the page isolation scanning step a compaction thread does is a lockless
+ * procedure (from a page standpoint), it might bring some racy situations while
+ * performing balloon page compaction. In order to sort out these racy scenarios
+ * and safely perform balloon's page compaction and migration we must, always,
+ * ensure following these three simple rules:
+ *
+ *   i. when updating a balloon's page ->mapping element, strictly do it under
+ *      the following lock order, independently of the far superior
+ *      locking scheme (lru_lock, balloon_lock):
+ *          +-page_lock(page);
+ *            +--spin_lock_irq(&b_dev_info->pages_lock);
+ *                  ... page->mapping updates here ...
+ *
+ *  ii. before isolating or dequeueing a balloon page from the balloon device
+ *      pages list, the page reference counter must be raised by one and the
+ *      extra refcount must be dropped when the page is enqueued back into
+ *      the balloon device page list, thus a balloon page keeps its reference
+ *      counter raised only while it is under our special handling;
+ *
+ * iii. after the lockless scan step have selected a potential balloon page for
+ *      isolation, re-test the page->mapping flags and the page ref counter
+ *      under the proper page lock, to ensure isolating a valid balloon page
+ *      (not yet isolated, nor under release procedure)
+ *
+ * The functions provided by this interface are placed to help on coping with
+ * the aforementioned balloon page corner case, as well as to ensure the simple
+ * set of exposed rules are satisfied while we are dealing with balloon pages
+ * compaction / migration.
+ *
+ * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
+ */
+#ifndef _LINUX_BALLOON_COMPACTION_H
+#define _LINUX_BALLOON_COMPACTION_H
+#include <linux/pagemap.h>
+#include <linux/page-flags.h>
+#include <linux/migrate.h>
+#include <linux/gfp.h>
+#include <linux/err.h>
+
+/*
+ * Balloon device information descriptor.
+ * This struct is used to allow the common balloon compaction interface
+ * procedures to find the proper balloon device holding memory pages they'll
+ * have to cope for page compaction / migration, as well as it serves the
+ * balloon driver as a page book-keeper for its registered balloon devices.
+ */
+struct balloon_dev_info {
+        void *balloon_device;           /* balloon device descriptor */
+        struct address_space *mapping;  /* balloon special page->mapping */
+        unsigned long isolated_pages;   /* # of isolated pages for migration */
+        spinlock_t pages_lock;          /* Protection to pages list */
+        struct list_head pages;         /* Pages enqueued & handled to Host */
+};
+
+extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
+extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
+extern struct balloon_dev_info *balloon_devinfo_alloc(
+                                                void *balloon_dev_descriptor);
+
+static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info)
+{
+        kfree(b_dev_info);
+}
+
+/*
+ * balloon_page_free - release a balloon page back to the page free lists
+ * @page: ballooned page to be set free
+ *
+ * This function must be used to properly set free an isolated/dequeued balloon
+ * page at the end of a sucessful page migration, or at the balloon driver's
+ * page release procedure.
+ */
+static inline void balloon_page_free(struct page *page)
+{
+        /*
+         * Balloon pages always get an extra refcount before being isolated
+         * and before being dequeued to help on sorting out fortuite colisions
+         * between a thread attempting to isolate and another thread attempting
+         * to release the very same balloon page.
+         *
+         * Before we handle the page back to Buddy, lets drop its extra refcnt.
+         */
+        put_page(page);
+        __free_page(page);
+}
+
+#ifdef CONFIG_BALLOON_COMPACTION
+extern bool balloon_page_isolate(struct page *page);
+extern void balloon_page_putback(struct page *page);
+extern int balloon_page_migrate(struct page *newpage,
+                                struct page *page, enum migrate_mode mode);
+extern struct address_space
+*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
+                        const struct address_space_operations *a_ops);
+
+static inline void balloon_mapping_free(struct address_space *balloon_mapping)
+{
+        kfree(balloon_mapping);
+}
+
+/*
+ * page_flags_cleared - helper to perform balloon @page ->flags tests.
+ *
+ * As balloon pages are obtained from buddy and we do not play with page->flags
+ * at driver level (exception made when we get the page lock for compaction),
+ * we can safely identify a ballooned page by checking if the
+ * PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared.  This approach also
+ * helps us skip ballooned pages that are locked for compaction or release, thus
+ * mitigating their racy check at balloon_page_movable()
+ */
+static inline bool page_flags_cleared(struct page *page)
+{
+        return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP);
+}
+
+/*
+ * __is_movable_balloon_page - helper to perform @page mapping->flags tests
+ */
+static inline bool __is_movable_balloon_page(struct page *page)
+{
+        struct address_space *mapping = page->mapping;
+        return mapping_balloon(mapping);
+}
+
+/*
+ * balloon_page_movable - test page->mapping->flags to identify balloon pages
+ *                        that can be moved by compaction/migration.
+ *
+ * This function is used at core compaction's page isolation scheme, therefore
+ * most pages exposed to it are not enlisted as balloon pages and so, to avoid
+ * undesired side effects like racing against __free_pages(), we cannot afford
+ * holding the page locked while testing page->mapping->flags here.
+ *
+ * As we might return false positives in the case of a balloon page being just
+ * released under us, the page->mapping->flags need to be re-tested later,
+ * under the proper page lock, at the functions that will be coping with the
+ * balloon page case.
+ */
+static inline bool balloon_page_movable(struct page *page)
+{
+        /*
+         * Before dereferencing and testing mapping->flags, let's make sure
+         * this is not a page that uses ->mapping in a different way
+         */
+        if (page_flags_cleared(page) && !page_mapped(page) &&
+            page_count(page) == 1)
+                return __is_movable_balloon_page(page);
+
+        return false;
+}
+
+/*
+ * balloon_page_insert - insert a page into the balloon's page list and make
+ *                       the page->mapping assignment accordingly.
+ * @page    : page to be assigned as a 'balloon page'
+ * @mapping : allocated special 'balloon_mapping'
+ * @head    : balloon's device page list head
+ *
+ * Caller must ensure the page is locked and the spin_lock protecting balloon
+ * pages list is held before inserting a page into the balloon device.
+ */
+static inline void balloon_page_insert(struct page *page,
+                                       struct address_space *mapping,
+                                       struct list_head *head)
+{
+        page->mapping = mapping;
+        list_add(&page->lru, head);
+}
+
+/*
+ * balloon_page_delete - delete a page from balloon's page list and clear
+ *                       the page->mapping assignement accordingly.
+ * @page    : page to be released from balloon's page list
+ *
+ * Caller must ensure the page is locked and the spin_lock protecting balloon
+ * pages list is held before deleting a page from the balloon device.
+ */
+static inline void balloon_page_delete(struct page *page)
+{
+        page->mapping = NULL;
+        list_del(&page->lru);
+}
+
+/*
+ * balloon_page_device - get the b_dev_info descriptor for the balloon device
+ *                       that enqueues the given page.
+ */
+static inline struct balloon_dev_info *balloon_page_device(struct page *page)
+{
+        struct address_space *mapping = page->mapping;
+        if (likely(mapping))
+                return mapping->private_data;
+
+        return NULL;
+}
+
+static inline gfp_t balloon_mapping_gfp_mask(void)
+{
+        return GFP_HIGHUSER_MOVABLE;
+}
+
+static inline bool balloon_compaction_check(void)
+{
+        return true;
+}
+
+#else /* !CONFIG_BALLOON_COMPACTION */
+
+static inline void *balloon_mapping_alloc(void *balloon_device,
+                                const struct address_space_operations *a_ops)
+{
+        return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void balloon_mapping_free(struct address_space *balloon_mapping)
+{
+        return;
+}
+
+static inline void balloon_page_insert(struct page *page,
+                                       struct address_space *mapping,
+                                       struct list_head *head)
+{
+        list_add(&page->lru, head);
+}
+
+static inline void balloon_page_delete(struct page *page)
+{
+        list_del(&page->lru);
+}
+
+static inline bool balloon_page_movable(struct page *page)
+{
+        return false;
+}
+
+static inline bool balloon_page_isolate(struct page *page)
+{
+        return false;
+}
+
+static inline void balloon_page_putback(struct page *page)
+{
+        return;
+}
+
+static inline int balloon_page_migrate(struct page *newpage,
+                                struct page *page, enum migrate_mode mode)
+{
+        return 0;
+}
+
+static inline gfp_t balloon_mapping_gfp_mask(void)
+{
+        return GFP_HIGHUSER;
+}
+
+static inline bool balloon_compaction_check(void)
+{
+        return false;
+}
+#endif /* CONFIG_BALLOON_COMPACTION */
+#endif /* _LINUX_BALLOON_COMPACTION_H */
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a4e886d17f87..ce42847ed35f 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -11,8 +11,18 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **);
  * Return values from addresss_space_operations.migratepage():
  * - negative errno on page migration failure;
  * - zero on page migration success;
+ *
+ * The balloon page migration introduces this special case where a 'distinct'
+ * return code is used to flag a successful page migration to unmap_and_move().
+ * This approach is necessary because page migration can race against balloon
+ * deflation procedure, and for such case we could introduce a nasty page leak
+ * if a successfully migrated balloon page gets released concurrently with
+ * migration's unmap_and_move() wrap-up steps.
  */
 #define MIGRATEPAGE_SUCCESS             0
+#define MIGRATEPAGE_BALLOON_SUCCESS     1 /* special ret code for balloon page
+                                           * sucessful migration case.
+                                           */
 
 #ifdef CONFIG_MIGRATION
 
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e42c762f0dc7..6da609d14c15 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -24,6 +24,7 @@ enum mapping_flags {
         AS_ENOSPC       = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
         AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
         AS_UNEVICTABLE  = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
+        AS_BALLOON_MAP  = __GFP_BITS_SHIFT + 4, /* balloon page special map */
 };
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -53,6 +54,21 @@ static inline int mapping_unevictable(struct address_space *mapping)
         return !!mapping;
 }
 
+static inline void mapping_set_balloon(struct address_space *mapping)
+{
+        set_bit(AS_BALLOON_MAP, &mapping->flags);
+}
+
+static inline void mapping_clear_balloon(struct address_space *mapping)
+{
+        clear_bit(AS_BALLOON_MAP, &mapping->flags);
+}
+
+static inline int mapping_balloon(struct address_space *mapping)
+{
+        return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
         return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
diff --git a/mm/Kconfig b/mm/Kconfig
index a3f8dddaaab3..e6651c5de14f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -188,6 +188,21 @@ config SPLIT_PTLOCK_CPUS
         default "4"
 
 #
+# support for memory balloon compaction
+config BALLOON_COMPACTION
+        bool "Allow for balloon memory compaction/migration"
+        def_bool y
+        depends on COMPACTION && VIRTIO_BALLOON
+        help
+          Memory fragmentation introduced by ballooning might reduce
+          significantly the number of 2MB contiguous memory blocks that can be
+          used within a guest, thus imposing performance penalties associated
+          with the reduced number of transparent huge pages that could be used
+          by the guest workload. Allowing the compaction & migration for memory
+          pages enlisted as being part of memory balloon devices avoids the
+          scenario aforementioned and helps improving memory defragmentation.
+
+#
 # support for memory compaction
 config COMPACTION
         bool "Allow for memory compaction"
diff --git a/mm/Makefile b/mm/Makefile
index 6b025f80af34..3a4628751f89 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -16,7 +16,8 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
                            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 interval_tree.o $(mmu-y)
+                           compaction.o balloon_compaction.o \
+                           interval_tree.o $(mmu-y)
 
 obj-y += init-mm.o
 
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
new file mode 100644
index 000000000000..07dbc8ec46cf
--- /dev/null
+++ b/mm/balloon_compaction.c
@@ -0,0 +1,302 @@
+/*
+ * mm/balloon_compaction.c
+ *
+ * Common interface for making balloon pages movable by compaction.
+ *
+ * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
+ */
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+#include <linux/balloon_compaction.h>
+
+/*
+ * balloon_devinfo_alloc - allocates a balloon device information descriptor.
+ * @balloon_dev_descriptor: pointer to reference the balloon device which
+ *                          this struct balloon_dev_info will be servicing.
+ *
+ * Driver must call it to properly allocate and initialize an instance of
+ * struct balloon_dev_info which will be used to reference a balloon device
+ * as well as to keep track of the balloon device page list.
+ */
+struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
+{
+        struct balloon_dev_info *b_dev_info;
+        b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
+        if (!b_dev_info)
+                return ERR_PTR(-ENOMEM);
+
+        b_dev_info->balloon_device = balloon_dev_descriptor;
+        b_dev_info->mapping = NULL;
+        b_dev_info->isolated_pages = 0;
+        spin_lock_init(&b_dev_info->pages_lock);
+        INIT_LIST_HEAD(&b_dev_info->pages);
+
+        return b_dev_info;
+}
+EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
+
+/*
+ * balloon_page_enqueue - allocates a new page and inserts it into the balloon
+ *                        page list.
+ * @b_dev_info: balloon device decriptor where we will insert a new page to
+ *
+ * Driver must call it to properly allocate a new enlisted balloon page
+ * before definetively removing it from the guest system.
+ * This function returns the page address for the recently enqueued page or
+ * NULL in the case we fail to allocate a new page this turn.
+ */
+struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
+{
+        unsigned long flags;
+        struct page *page = alloc_page(balloon_mapping_gfp_mask() |
+                                        __GFP_NOMEMALLOC | __GFP_NORETRY);
+        if (!page)
+                return NULL;
+
+        /*
+         * Block others from accessing the 'page' when we get around to
+         * establishing additional references. We should be the only one
+         * holding a reference to the 'page' at this point.
+         */
+        BUG_ON(!trylock_page(page));
+        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+        balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
+        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+        unlock_page(page);
+        return page;
+}
+EXPORT_SYMBOL_GPL(balloon_page_enqueue);
+
+/*
+ * balloon_page_dequeue - removes a page from balloon's page list and returns
+ *                        the its address to allow the driver release the page.
+ * @b_dev_info: balloon device decriptor where we will grab a page from.
+ *
+ * Driver must call it to properly de-allocate a previous enlisted balloon page
+ * before definetively releasing it back to the guest system.
+ * This function returns the page address for the recently dequeued page or
+ * NULL in the case we find balloon's page list temporarily empty due to
+ * compaction isolated pages.
+ */
+struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
+{
+        struct page *page, *tmp;
+        unsigned long flags;
+        bool dequeued_page;
+
+        dequeued_page = false;
+        list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
+                /*
+                 * Block others from accessing the 'page' while we get around
+                 * establishing additional references and preparing the 'page'
+                 * to be released by the balloon driver.
+                 */
+                if (trylock_page(page)) {
+                        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+                        /*
+                         * Raise the page refcount here to prevent any wrong
+                         * attempt to isolate this page, in case of coliding
+                         * with balloon_page_isolate() just after we release
+                         * the page lock.
+                         *
+                         * balloon_page_free() will take care of dropping
+                         * this extra refcount later.
+                         */
+                        get_page(page);
+                        balloon_page_delete(page);
+                        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+                        unlock_page(page);
+                        dequeued_page = true;
+                        break;
+                }
+        }
+
+        if (!dequeued_page) {
+                /*
+                 * If we are unable to dequeue a balloon page because the page
+                 * list is empty and there is no isolated pages, then something
+                 * went out of track and some balloon pages are lost.
+                 * BUG() here, otherwise the balloon driver may get stuck into
+                 * an infinite loop while attempting to release all its pages.
+                 */
+                spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+                if (unlikely(list_empty(&b_dev_info->pages) &&
+                             !b_dev_info->isolated_pages))
+                        BUG();
+                spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+                page = NULL;
+        }
+        return page;
+}
+EXPORT_SYMBOL_GPL(balloon_page_dequeue);
+
+#ifdef CONFIG_BALLOON_COMPACTION
+/*
+ * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
+ * @b_dev_info: holds the balloon device information descriptor.
+ * @a_ops: balloon_mapping address_space_operations descriptor.
+ *
+ * Driver must call it to properly allocate and initialize an instance of
+ * struct address_space which will be used as the special page->mapping for
+ * balloon device enlisted page instances.
+ */
+struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
+                                const struct address_space_operations *a_ops)
+{
+        struct address_space *mapping;
+
+        mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
+        if (!mapping)
+                return ERR_PTR(-ENOMEM);
+
+        /*
+         * Give a clean 'zeroed' status to all elements of this special
+         * balloon page->mapping struct address_space instance.
+         */
+        address_space_init_once(mapping);
+
+        /*
+         * Set mapping->flags appropriately, to allow balloon pages
+         * ->mapping identification.
+         */
+        mapping_set_balloon(mapping);
+        mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
+
+        /* balloon's page->mapping->a_ops callback descriptor */
+        mapping->a_ops = a_ops;
+
+        /*
+         * Establish a pointer reference back to the balloon device descriptor
+         * this particular page->mapping will be servicing.
+         * This is used by compaction / migration procedures to identify and
+         * access the balloon device pageset while isolating / migrating pages.
+         *
+         * As some balloon drivers can register multiple balloon devices
+         * for a single guest, this also helps compaction / migration to
+         * properly deal with multiple balloon pagesets, when required.
+         */
+        mapping->private_data = b_dev_info;
+        b_dev_info->mapping = mapping;
+
+        return mapping;
+}
+EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
+
+static inline void __isolate_balloon_page(struct page *page)
+{
+        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        unsigned long flags;
+        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+        list_del(&page->lru);
+        b_dev_info->isolated_pages++;
+        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+}
+
+static inline void __putback_balloon_page(struct page *page)
+{
+        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        unsigned long flags;
+        spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+        list_add(&page->lru, &b_dev_info->pages);
+        b_dev_info->isolated_pages--;
+        spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+}
+
+static inline int __migrate_balloon_page(struct address_space *mapping,
+                struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+        return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
+}
+
+/* __isolate_lru_page() counterpart for a ballooned page */
+bool balloon_page_isolate(struct page *page)
+{
+        /*
+         * Avoid burning cycles with pages that are yet under __free_pages(),
+         * or just got freed under us.
+         *
+         * In case we 'win' a race for a balloon page being freed under us and
+         * raise its refcount preventing __free_pages() from doing its job
+         * the put_page() at the end of this block will take care of
+         * release this page, thus avoiding a nasty leakage.
+         */
+        if (likely(get_page_unless_zero(page))) {
+                /*
+                 * As balloon pages are not isolated from LRU lists, concurrent
+                 * compaction threads can race against page migration functions
+                 * as well as race against the balloon driver releasing a page.
+                 *
+                 * In order to avoid having an already isolated balloon page
+                 * being (wrongly) re-isolated while it is under migration,
+                 * or to avoid attempting to isolate pages being released by
+                 * the balloon driver, lets be sure we have the page lock
+                 * before proceeding with the balloon page isolation steps.
+                 */
+                if (likely(trylock_page(page))) {
+                        /*
+                         * A ballooned page, by default, has just one refcount.
+                         * Prevent concurrent compaction threads from isolating
+                         * an already isolated balloon page by refcount check.
+                         */
+                        if (__is_movable_balloon_page(page) &&
+                            page_count(page) == 2) {
+                                __isolate_balloon_page(page);
+                                unlock_page(page);
+                                return true;
+                        }
+                        unlock_page(page);
+                }
+                put_page(page);
+        }
+        return false;
+}
+
+/* putback_lru_page() counterpart for a ballooned page */
+void balloon_page_putback(struct page *page)
+{
+        /*
+         * 'lock_page()' stabilizes the page and prevents races against
+         * concurrent isolation threads attempting to re-isolate it.
+         */
+        lock_page(page);
+
+        if (__is_movable_balloon_page(page)) {
+                __putback_balloon_page(page);
+                /* drop the extra ref count taken for page isolation */
+                put_page(page);
+        } else {
+                WARN_ON(1);
+                dump_page(page);
+        }
+        unlock_page(page);
+}
+
+/* move_to_new_page() counterpart for a ballooned page */
+int balloon_page_migrate(struct page *newpage,
+                         struct page *page, enum migrate_mode mode)
+{
+        struct address_space *mapping;
+        int rc = -EAGAIN;
+
+        /*
+         * Block others from accessing the 'newpage' when we get around to
+         * establishing additional references. We should be the only one
+         * holding a reference to the 'newpage' at this point.
+         */
+        BUG_ON(!trylock_page(newpage));
+
+        if (WARN_ON(!__is_movable_balloon_page(page))) {
+                dump_page(page);
+                unlock_page(newpage);
+                return rc;
+        }
+
+        mapping = page->mapping;
+        if (mapping)
+                rc = __migrate_balloon_page(mapping, newpage, page, mode);
+
+        unlock_page(newpage);
+        return rc;
+}
+#endif /* CONFIG_BALLOON_COMPACTION */