diff --git a/mm/backing-dev.c b/mm/backing-dev.c
new file mode 100644
index 0000000..8a8bb87
--- /dev/null
+++ b/mm/backing-dev.c
@@ -0,0 +1,1080 @@
+
+#include <linux/wait.h>
+#include <linux/backing-dev.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/writeback.h>
+#include <linux/device.h>
+#include <trace/events/writeback.h>
+
+struct backing_dev_info noop_backing_dev_info = {
+	.name		= "noop",
+	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
+};
+EXPORT_SYMBOL_GPL(noop_backing_dev_info);
+
+static struct class *bdi_class;
+
+/*
+ * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
+ * locking.
+ */
+DEFINE_SPINLOCK(bdi_lock);
+LIST_HEAD(bdi_list);
+
+/* bdi_wq serves all asynchronous writeback tasks */
+struct workqueue_struct *bdi_wq;
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+static struct dentry *bdi_debug_root;
+
+static void bdi_debug_init(void)
+{
+	bdi_debug_root = debugfs_create_dir("bdi", NULL);
+}
+
+static int bdi_debug_stats_show(struct seq_file *m, void *v)
+{
+	struct backing_dev_info *bdi = m->private;
+	struct bdi_writeback *wb = &bdi->wb;
+	unsigned long background_thresh;
+	unsigned long dirty_thresh;
+	unsigned long wb_thresh;
+	unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;
+	struct inode *inode;
+
+	nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;
+	spin_lock(&wb->list_lock);
+	list_for_each_entry(inode, &wb->b_dirty, i_io_list)
+		nr_dirty++;
+	list_for_each_entry(inode, &wb->b_io, i_io_list)
+		nr_io++;
+	list_for_each_entry(inode, &wb->b_more_io, i_io_list)
+		nr_more_io++;
+	list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)
+		if (inode->i_state & I_DIRTY_TIME)
+			nr_dirty_time++;
+	spin_unlock(&wb->list_lock);
+
+	global_dirty_limits(&background_thresh, &dirty_thresh);
+	wb_thresh = wb_calc_thresh(wb, dirty_thresh);
+
+#define K(x) ((x) << (PAGE_SHIFT - 10))
+	seq_printf(m,
+		   "BdiWriteback:       %10lu kB\n"
+		   "BdiReclaimable:     %10lu kB\n"
+		   "BdiDirtyThresh:     %10lu kB\n"
+		   "DirtyThresh:        %10lu kB\n"
+		   "BackgroundThresh:   %10lu kB\n"
+		   "BdiDirtied:         %10lu kB\n"
+		   "BdiWritten:         %10lu kB\n"
+		   "BdiWriteBandwidth:  %10lu kBps\n"
+		   "b_dirty:            %10lu\n"
+		   "b_io:               %10lu\n"
+		   "b_more_io:          %10lu\n"
+		   "b_dirty_time:       %10lu\n"
+		   "bdi_list:           %10u\n"
+		   "state:              %10lx\n",
+		   (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
+		   (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
+		   K(wb_thresh),
+		   K(dirty_thresh),
+		   K(background_thresh),
+		   (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
+		   (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
+		   (unsigned long) K(wb->write_bandwidth),
+		   nr_dirty,
+		   nr_io,
+		   nr_more_io,
+		   nr_dirty_time,
+		   !list_empty(&bdi->bdi_list), bdi->wb.state);
+#undef K
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
+
+static int bdi_debug_register(struct backing_dev_info *bdi, const char *name)
+{
+	if (!bdi_debug_root)
+		return -ENOMEM;
+
+	bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
+	if (!bdi->debug_dir)
+		return -ENOMEM;
+
+	bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
+					       bdi, &bdi_debug_stats_fops);
+	if (!bdi->debug_stats) {
+		debugfs_remove(bdi->debug_dir);
+		bdi->debug_dir = NULL;
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void bdi_debug_unregister(struct backing_dev_info *bdi)
+{
+	debugfs_remove(bdi->debug_stats);
+	debugfs_remove(bdi->debug_dir);
+}
+#else
+static inline void bdi_debug_init(void)
+{
+}
+static inline int bdi_debug_register(struct backing_dev_info *bdi,
+				      const char *name)
+{
+	return 0;
+}
+static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
+{
+}
+#endif
+
+static ssize_t read_ahead_kb_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+	unsigned long read_ahead_kb;
+	ssize_t ret;
+
+	ret = kstrtoul(buf, 10, &read_ahead_kb);
+	if (ret < 0)
+		return ret;
+
+	bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
+
+	return count;
+}
+
+#define K(pages) ((pages) << (PAGE_SHIFT - 10))
+
+#define BDI_SHOW(name, expr)						\
+static ssize_t name##_show(struct device *dev,				\
+			   struct device_attribute *attr, char *page)	\
+{									\
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);		\
+									\
+	return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);	\
+}									\
+static DEVICE_ATTR_RW(name);
+
+BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
+
+static ssize_t min_ratio_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+	unsigned int ratio;
+	ssize_t ret;
+
+	ret = kstrtouint(buf, 10, &ratio);
+	if (ret < 0)
+		return ret;
+
+	ret = bdi_set_min_ratio(bdi, ratio);
+	if (!ret)
+		ret = count;
+
+	return ret;
+}
+BDI_SHOW(min_ratio, bdi->min_ratio)
+
+static ssize_t max_ratio_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+	unsigned int ratio;
+	ssize_t ret;
+
+	ret = kstrtouint(buf, 10, &ratio);
+	if (ret < 0)
+		return ret;
+
+	ret = bdi_set_max_ratio(bdi, ratio);
+	if (!ret)
+		ret = count;
+
+	return ret;
+}
+BDI_SHOW(max_ratio, bdi->max_ratio)
+
+static ssize_t stable_pages_required_show(struct device *dev,
+					  struct device_attribute *attr,
+					  char *page)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+
+	return snprintf(page, PAGE_SIZE-1, "%d\n",
+			bdi_cap_stable_pages_required(bdi) ? 1 : 0);
+}
+static DEVICE_ATTR_RO(stable_pages_required);
+
+static struct attribute *bdi_dev_attrs[] = {
+	&dev_attr_read_ahead_kb.attr,
+	&dev_attr_min_ratio.attr,
+	&dev_attr_max_ratio.attr,
+	&dev_attr_stable_pages_required.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(bdi_dev);
+
+static __init int bdi_class_init(void)
+{
+	bdi_class = class_create(THIS_MODULE, "bdi");
+	if (IS_ERR(bdi_class))
+		return PTR_ERR(bdi_class);
+
+	bdi_class->dev_groups = bdi_dev_groups;
+	bdi_debug_init();
+
+	return 0;
+}
+postcore_initcall(bdi_class_init);
+
+static int bdi_init(struct backing_dev_info *bdi);
+
+static int __init default_bdi_init(void)
+{
+	int err;
+
+	bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
+					      WQ_UNBOUND | WQ_SYSFS, 0);
+	if (!bdi_wq)
+		return -ENOMEM;
+
+	err = bdi_init(&noop_backing_dev_info);
+
+	return err;
+}
+subsys_initcall(default_bdi_init);
+
+/*
+ * This function is used when the first inode for this wb is marked dirty. It
+ * wakes-up the corresponding bdi thread which should then take care of the
+ * periodic background write-out of dirty inodes. Since the write-out would
+ * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
+ * set up a timer which wakes the bdi thread up later.
+ *
+ * Note, we wouldn't bother setting up the timer, but this function is on the
+ * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
+ * by delaying the wake-up.
+ *
+ * We have to be careful not to postpone flush work if it is scheduled for
+ * earlier. Thus we use queue_delayed_work().
+ */
+void wb_wakeup_delayed(struct bdi_writeback *wb)
+{
+	unsigned long timeout;
+
+	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
+	spin_lock_bh(&wb->work_lock);
+	if (test_bit(WB_registered, &wb->state))
+		queue_delayed_work(bdi_wq, &wb->dwork, timeout);
+	spin_unlock_bh(&wb->work_lock);
+}
+
+/*
+ * Initial write bandwidth: 100 MB/s
+ */
+#define INIT_BW		(100 << (20 - PAGE_SHIFT))
+
+static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
+		   int blkcg_id, gfp_t gfp)
+{
+	int i, err;
+
+	memset(wb, 0, sizeof(*wb));
+
+	if (wb != &bdi->wb)
+		bdi_get(bdi);
+	wb->bdi = bdi;
+	wb->last_old_flush = jiffies;
+	INIT_LIST_HEAD(&wb->b_dirty);
+	INIT_LIST_HEAD(&wb->b_io);
+	INIT_LIST_HEAD(&wb->b_more_io);
+	INIT_LIST_HEAD(&wb->b_dirty_time);
+	spin_lock_init(&wb->list_lock);
+
+	wb->bw_time_stamp = jiffies;
+	wb->balanced_dirty_ratelimit = INIT_BW;
+	wb->dirty_ratelimit = INIT_BW;
+	wb->write_bandwidth = INIT_BW;
+	wb->avg_write_bandwidth = INIT_BW;
+
+	spin_lock_init(&wb->work_lock);
+	INIT_LIST_HEAD(&wb->work_list);
+	INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
+	wb->dirty_sleep = jiffies;
+
+	wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);
+	if (!wb->congested) {
+		err = -ENOMEM;
+		goto out_put_bdi;
+	}
+
+	err = fprop_local_init_percpu(&wb->completions, gfp);
+	if (err)
+		goto out_put_cong;
+
+	for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
+		err = percpu_counter_init(&wb->stat[i], 0, gfp);
+		if (err)
+			goto out_destroy_stat;
+	}
+
+	return 0;
+
+out_destroy_stat:
+	while (i--)
+		percpu_counter_destroy(&wb->stat[i]);
+	fprop_local_destroy_percpu(&wb->completions);
+out_put_cong:
+	wb_congested_put(wb->congested);
+out_put_bdi:
+	if (wb != &bdi->wb)
+		bdi_put(bdi);
+	return err;
+}
+
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
+
+/*
+ * Remove bdi from the global list and shutdown any threads we have running
+ */
+static void wb_shutdown(struct bdi_writeback *wb)
+{
+	/* Make sure nobody queues further work */
+	spin_lock_bh(&wb->work_lock);
+	if (!test_and_clear_bit(WB_registered, &wb->state)) {
+		spin_unlock_bh(&wb->work_lock);
+		return;
+	}
+	spin_unlock_bh(&wb->work_lock);
+
+	cgwb_remove_from_bdi_list(wb);
+	/*
+	 * Drain work list and shutdown the delayed_work.  !WB_registered
+	 * tells wb_workfn() that @wb is dying and its work_list needs to
+	 * be drained no matter what.
+	 */
+	mod_delayed_work(bdi_wq, &wb->dwork, 0);
+	flush_delayed_work(&wb->dwork);
+	WARN_ON(!list_empty(&wb->work_list));
+}
+
+static void wb_exit(struct bdi_writeback *wb)
+{
+	int i;
+
+	WARN_ON(delayed_work_pending(&wb->dwork));
+
+	for (i = 0; i < NR_WB_STAT_ITEMS; i++)
+		percpu_counter_destroy(&wb->stat[i]);
+
+	fprop_local_destroy_percpu(&wb->completions);
+	wb_congested_put(wb->congested);
+	if (wb != &wb->bdi->wb)
+		bdi_put(wb->bdi);
+}
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+
+#include <linux/memcontrol.h>
+
+/*
+ * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
+ * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU
+ * protected.
+ */
+static DEFINE_SPINLOCK(cgwb_lock);
+static struct workqueue_struct *cgwb_release_wq;
+
+/**
+ * wb_congested_get_create - get or create a wb_congested
+ * @bdi: associated bdi
+ * @blkcg_id: ID of the associated blkcg
+ * @gfp: allocation mask
+ *
+ * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
+ * The returned wb_congested has its reference count incremented.  Returns
+ * NULL on failure.
+ */
+struct bdi_writeback_congested *
+wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
+{
+	struct bdi_writeback_congested *new_congested = NULL, *congested;
+	struct rb_node **node, *parent;
+	unsigned long flags;
+retry:
+	spin_lock_irqsave(&cgwb_lock, flags);
+
+	node = &bdi->cgwb_congested_tree.rb_node;
+	parent = NULL;
+
+	while (*node != NULL) {
+		parent = *node;
+		congested = rb_entry(parent, struct bdi_writeback_congested,
+				     rb_node);
+		if (congested->blkcg_id < blkcg_id)
+			node = &parent->rb_left;
+		else if (congested->blkcg_id > blkcg_id)
+			node = &parent->rb_right;
+		else
+			goto found;
+	}
+
+	if (new_congested) {
+		/* !found and storage for new one already allocated, insert */
+		congested = new_congested;
+		rb_link_node(&congested->rb_node, parent, node);
+		rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
+		spin_unlock_irqrestore(&cgwb_lock, flags);
+		return congested;
+	}
+
+	spin_unlock_irqrestore(&cgwb_lock, flags);
+
+	/* allocate storage for new one and retry */
+	new_congested = kzalloc(sizeof(*new_congested), gfp);
+	if (!new_congested)
+		return NULL;
+
+	refcount_set(&new_congested->refcnt, 1);
+	new_congested->__bdi = bdi;
+	new_congested->blkcg_id = blkcg_id;
+	goto retry;
+
+found:
+	refcount_inc(&congested->refcnt);
+	spin_unlock_irqrestore(&cgwb_lock, flags);
+	kfree(new_congested);
+	return congested;
+}
+
+/**
+ * wb_congested_put - put a wb_congested
+ * @congested: wb_congested to put
+ *
+ * Put @congested and destroy it if the refcnt reaches zero.
+ */
+void wb_congested_put(struct bdi_writeback_congested *congested)
+{
+	unsigned long flags;
+
+	if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags))
+		return;
+
+	/* bdi might already have been destroyed leaving @congested unlinked */
+	if (congested->__bdi) {
+		rb_erase(&congested->rb_node,
+			 &congested->__bdi->cgwb_congested_tree);
+		congested->__bdi = NULL;
+	}
+
+	spin_unlock_irqrestore(&cgwb_lock, flags);
+	kfree(congested);
+}
+
+static void cgwb_release_workfn(struct work_struct *work)
+{
+	struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
+						release_work);
+	struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css);
+
+	mutex_lock(&wb->bdi->cgwb_release_mutex);
+	wb_shutdown(wb);
+
+	css_put(wb->memcg_css);
+	css_put(wb->blkcg_css);
+	mutex_unlock(&wb->bdi->cgwb_release_mutex);
+
+	/* triggers blkg destruction if cgwb_refcnt becomes zero */
+	blkcg_cgwb_put(blkcg);
+
+	fprop_local_destroy_percpu(&wb->memcg_completions);
+	percpu_ref_exit(&wb->refcnt);
+	wb_exit(wb);
+	kfree_rcu(wb, rcu);
+}
+
+static void cgwb_release(struct percpu_ref *refcnt)
+{
+	struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
+						refcnt);
+	queue_work(cgwb_release_wq, &wb->release_work);
+}
+
+static void cgwb_kill(struct bdi_writeback *wb)
+{
+	lockdep_assert_held(&cgwb_lock);
+
+	WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
+	list_del(&wb->memcg_node);
+	list_del(&wb->blkcg_node);
+	percpu_ref_kill(&wb->refcnt);
+}
+
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
+{
+	spin_lock_irq(&cgwb_lock);
+	list_del_rcu(&wb->bdi_node);
+	spin_unlock_irq(&cgwb_lock);
+}
+
+static int cgwb_create(struct backing_dev_info *bdi,
+		       struct cgroup_subsys_state *memcg_css, gfp_t gfp)
+{
+	struct mem_cgroup *memcg;
+	struct cgroup_subsys_state *blkcg_css;
+	struct blkcg *blkcg;
+	struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
+	struct bdi_writeback *wb;
+	unsigned long flags;
+	int ret = 0;
+
+	memcg = mem_cgroup_from_css(memcg_css);
+	blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
+	blkcg = css_to_blkcg(blkcg_css);
+	memcg_cgwb_list = &memcg->cgwb_list;
+	blkcg_cgwb_list = &blkcg->cgwb_list;
+
+	/* look up again under lock and discard on blkcg mismatch */
+	spin_lock_irqsave(&cgwb_lock, flags);
+	wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+	if (wb && wb->blkcg_css != blkcg_css) {
+		cgwb_kill(wb);
+		wb = NULL;
+	}
+	spin_unlock_irqrestore(&cgwb_lock, flags);
+	if (wb)
+		goto out_put;
+
+	/* need to create a new one */
+	wb = kmalloc(sizeof(*wb), gfp);
+	if (!wb) {
+		ret = -ENOMEM;
+		goto out_put;
+	}
+
+	ret = wb_init(wb, bdi, blkcg_css->id, gfp);
+	if (ret)
+		goto err_free;
+
+	ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
+	if (ret)
+		goto err_wb_exit;
+
+	ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
+	if (ret)
+		goto err_ref_exit;
+
+	wb->memcg_css = memcg_css;
+	wb->blkcg_css = blkcg_css;
+	INIT_WORK(&wb->release_work, cgwb_release_workfn);
+	set_bit(WB_registered, &wb->state);
+
+	/*
+	 * The root wb determines the registered state of the whole bdi and
+	 * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
+	 * whether they're still online.  Don't link @wb if any is dead.
+	 * See wb_memcg_offline() and wb_blkcg_offline().
+	 */
+	ret = -ENODEV;
+	spin_lock_irqsave(&cgwb_lock, flags);
+	if (test_bit(WB_registered, &bdi->wb.state) &&
+	    blkcg_cgwb_list->next && memcg_cgwb_list->next) {
+		/* we might have raced another instance of this function */
+		ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
+		if (!ret) {
+			list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
+			list_add(&wb->memcg_node, memcg_cgwb_list);
+			list_add(&wb->blkcg_node, blkcg_cgwb_list);
+			blkcg_cgwb_get(blkcg);
+			css_get(memcg_css);
+			css_get(blkcg_css);
+		}
+	}
+	spin_unlock_irqrestore(&cgwb_lock, flags);
+	if (ret) {
+		if (ret == -EEXIST)
+			ret = 0;
+		goto err_fprop_exit;
+	}
+	goto out_put;
+
+err_fprop_exit:
+	fprop_local_destroy_percpu(&wb->memcg_completions);
+err_ref_exit:
+	percpu_ref_exit(&wb->refcnt);
+err_wb_exit:
+	wb_exit(wb);
+err_free:
+	kfree(wb);
+out_put:
+	css_put(blkcg_css);
+	return ret;
+}
+
+/**
+ * wb_get_create - get wb for a given memcg, create if necessary
+ * @bdi: target bdi
+ * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
+ * @gfp: allocation mask to use
+ *
+ * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
+ * create one.  The returned wb has its refcount incremented.
+ *
+ * This function uses css_get() on @memcg_css and thus expects its refcnt
+ * to be positive on invocation.  IOW, rcu_read_lock() protection on
+ * @memcg_css isn't enough.  try_get it before calling this function.
+ *
+ * A wb is keyed by its associated memcg.  As blkcg implicitly enables
+ * memcg on the default hierarchy, memcg association is guaranteed to be
+ * more specific (equal or descendant to the associated blkcg) and thus can
+ * identify both the memcg and blkcg associations.
+ *
+ * Because the blkcg associated with a memcg may change as blkcg is enabled
+ * and disabled closer to root in the hierarchy, each wb keeps track of
+ * both the memcg and blkcg associated with it and verifies the blkcg on
+ * each lookup.  On mismatch, the existing wb is discarded and a new one is
+ * created.
+ */
+struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
+				    struct cgroup_subsys_state *memcg_css,
+				    gfp_t gfp)
+{
+	struct bdi_writeback *wb;
+
+	might_sleep_if(gfpflags_allow_blocking(gfp));
+
+	if (!memcg_css->parent)
+		return &bdi->wb;
+
+	do {
+		rcu_read_lock();
+		wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+		if (wb) {
+			struct cgroup_subsys_state *blkcg_css;
+
+			/* see whether the blkcg association has changed */
+			blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
+						     &io_cgrp_subsys);
+			if (unlikely(wb->blkcg_css != blkcg_css ||
+				     !wb_tryget(wb)))
+				wb = NULL;
+			css_put(blkcg_css);
+		}
+		rcu_read_unlock();
+	} while (!wb && !cgwb_create(bdi, memcg_css, gfp));
+
+	return wb;
+}
+
+static int cgwb_bdi_init(struct backing_dev_info *bdi)
+{
+	int ret;
+
+	INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
+	bdi->cgwb_congested_tree = RB_ROOT;
+	mutex_init(&bdi->cgwb_release_mutex);
+
+	ret = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
+	if (!ret) {
+		bdi->wb.memcg_css = &root_mem_cgroup->css;
+		bdi->wb.blkcg_css = blkcg_root_css;
+	}
+	return ret;
+}
+
+static void cgwb_bdi_unregister(struct backing_dev_info *bdi)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	struct bdi_writeback *wb;
+
+	WARN_ON(test_bit(WB_registered, &bdi->wb.state));
+
+	spin_lock_irq(&cgwb_lock);
+	radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
+		cgwb_kill(*slot);
+	spin_unlock_irq(&cgwb_lock);
+
+	mutex_lock(&bdi->cgwb_release_mutex);
+	spin_lock_irq(&cgwb_lock);
+	while (!list_empty(&bdi->wb_list)) {
+		wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
+				      bdi_node);
+		spin_unlock_irq(&cgwb_lock);
+		wb_shutdown(wb);
+		spin_lock_irq(&cgwb_lock);
+	}
+	spin_unlock_irq(&cgwb_lock);
+	mutex_unlock(&bdi->cgwb_release_mutex);
+}
+
+/**
+ * wb_memcg_offline - kill all wb's associated with a memcg being offlined
+ * @memcg: memcg being offlined
+ *
+ * Also prevents creation of any new wb's associated with @memcg.
+ */
+void wb_memcg_offline(struct mem_cgroup *memcg)
+{
+	struct list_head *memcg_cgwb_list = &memcg->cgwb_list;
+	struct bdi_writeback *wb, *next;
+
+	spin_lock_irq(&cgwb_lock);
+	list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
+		cgwb_kill(wb);
+	memcg_cgwb_list->next = NULL;	/* prevent new wb's */
+	spin_unlock_irq(&cgwb_lock);
+}
+
+/**
+ * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
+ * @blkcg: blkcg being offlined
+ *
+ * Also prevents creation of any new wb's associated with @blkcg.
+ */
+void wb_blkcg_offline(struct blkcg *blkcg)
+{
+	struct bdi_writeback *wb, *next;
+
+	spin_lock_irq(&cgwb_lock);
+	list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
+		cgwb_kill(wb);
+	blkcg->cgwb_list.next = NULL;	/* prevent new wb's */
+	spin_unlock_irq(&cgwb_lock);
+}
+
+static void cgwb_bdi_exit(struct backing_dev_info *bdi)
+{
+	struct rb_node *rbn;
+
+	spin_lock_irq(&cgwb_lock);
+	while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
+		struct bdi_writeback_congested *congested =
+			rb_entry(rbn, struct bdi_writeback_congested, rb_node);
+
+		rb_erase(rbn, &bdi->cgwb_congested_tree);
+		congested->__bdi = NULL;	/* mark @congested unlinked */
+	}
+	spin_unlock_irq(&cgwb_lock);
+}
+
+static void cgwb_bdi_register(struct backing_dev_info *bdi)
+{
+	spin_lock_irq(&cgwb_lock);
+	list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
+	spin_unlock_irq(&cgwb_lock);
+}
+
+static int __init cgwb_init(void)
+{
+	/*
+	 * There can be many concurrent release work items overwhelming
+	 * system_wq.  Put them in a separate wq and limit concurrency.
+	 * There's no point in executing many of these in parallel.
+	 */
+	cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
+	if (!cgwb_release_wq)
+		return -ENOMEM;
+
+	return 0;
+}
+subsys_initcall(cgwb_init);
+
+#else	/* CONFIG_CGROUP_WRITEBACK */
+
+static int cgwb_bdi_init(struct backing_dev_info *bdi)
+{
+	int err;
+
+	bdi->wb_congested = kzalloc(sizeof(*bdi->wb_congested), GFP_KERNEL);
+	if (!bdi->wb_congested)
+		return -ENOMEM;
+
+	refcount_set(&bdi->wb_congested->refcnt, 1);
+
+	err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
+	if (err) {
+		wb_congested_put(bdi->wb_congested);
+		return err;
+	}
+	return 0;
+}
+
+static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
+
+static void cgwb_bdi_exit(struct backing_dev_info *bdi)
+{
+	wb_congested_put(bdi->wb_congested);
+}
+
+static void cgwb_bdi_register(struct backing_dev_info *bdi)
+{
+	list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
+}
+
+static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
+{
+	list_del_rcu(&wb->bdi_node);
+}
+
+#endif	/* CONFIG_CGROUP_WRITEBACK */
+
+static int bdi_init(struct backing_dev_info *bdi)
+{
+	int ret;
+
+	bdi->dev = NULL;
+
+	kref_init(&bdi->refcnt);
+	bdi->min_ratio = 0;
+	bdi->max_ratio = 100;
+	bdi->max_prop_frac = FPROP_FRAC_BASE;
+	INIT_LIST_HEAD(&bdi->bdi_list);
+	INIT_LIST_HEAD(&bdi->wb_list);
+	init_waitqueue_head(&bdi->wb_waitq);
+
+	ret = cgwb_bdi_init(bdi);
+
+	return ret;
+}
+
+struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id)
+{
+	struct backing_dev_info *bdi;
+
+	bdi = kmalloc_node(sizeof(struct backing_dev_info),
+			   gfp_mask | __GFP_ZERO, node_id);
+	if (!bdi)
+		return NULL;
+
+	if (bdi_init(bdi)) {
+		kfree(bdi);
+		return NULL;
+	}
+	return bdi;
+}
+EXPORT_SYMBOL(bdi_alloc_node);
+
+int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
+{
+	struct device *dev;
+
+	if (bdi->dev)	/* The driver needs to use separate queues per device */
+		return 0;
+
+	dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	cgwb_bdi_register(bdi);
+	bdi->dev = dev;
+
+	bdi_debug_register(bdi, dev_name(dev));
+	set_bit(WB_registered, &bdi->wb.state);
+
+	spin_lock_bh(&bdi_lock);
+	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+	spin_unlock_bh(&bdi_lock);
+
+	trace_writeback_bdi_register(bdi);
+	return 0;
+}
+EXPORT_SYMBOL(bdi_register_va);
+
+int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...)
+{
+	va_list args;
+	int ret;
+
+	va_start(args, fmt);
+	ret = bdi_register_va(bdi, fmt, args);
+	va_end(args);
+	return ret;
+}
+EXPORT_SYMBOL(bdi_register);
+
+int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
+{
+	int rc;
+
+	rc = bdi_register(bdi, "%u:%u", MAJOR(owner->devt), MINOR(owner->devt));
+	if (rc)
+		return rc;
+	/* Leaking owner reference... */
+	WARN_ON(bdi->owner);
+	bdi->owner = owner;
+	get_device(owner);
+	return 0;
+}
+EXPORT_SYMBOL(bdi_register_owner);
+
+/*
+ * Remove bdi from bdi_list, and ensure that it is no longer visible
+ */
+static void bdi_remove_from_list(struct backing_dev_info *bdi)
+{
+	spin_lock_bh(&bdi_lock);
+	list_del_rcu(&bdi->bdi_list);
+	spin_unlock_bh(&bdi_lock);
+
+	synchronize_rcu_expedited();
+}
+
+void bdi_unregister(struct backing_dev_info *bdi)
+{
+	/* make sure nobody finds us on the bdi_list anymore */
+	bdi_remove_from_list(bdi);
+	wb_shutdown(&bdi->wb);
+	cgwb_bdi_unregister(bdi);
+
+	if (bdi->dev) {
+		bdi_debug_unregister(bdi);
+		device_unregister(bdi->dev);
+		bdi->dev = NULL;
+	}
+
+	if (bdi->owner) {
+		put_device(bdi->owner);
+		bdi->owner = NULL;
+	}
+}
+
+static void release_bdi(struct kref *ref)
+{
+	struct backing_dev_info *bdi =
+			container_of(ref, struct backing_dev_info, refcnt);
+
+	if (test_bit(WB_registered, &bdi->wb.state))
+		bdi_unregister(bdi);
+	WARN_ON_ONCE(bdi->dev);
+	wb_exit(&bdi->wb);
+	cgwb_bdi_exit(bdi);
+	kfree(bdi);
+}
+
+void bdi_put(struct backing_dev_info *bdi)
+{
+	kref_put(&bdi->refcnt, release_bdi);
+}
+EXPORT_SYMBOL(bdi_put);
+
+static wait_queue_head_t congestion_wqh[2] = {
+		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
+		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
+	};
+static atomic_t nr_wb_congested[2];
+
+void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)
+{
+	wait_queue_head_t *wqh = &congestion_wqh[sync];
+	enum wb_congested_state bit;
+
+	bit = sync ? WB_sync_congested : WB_async_congested;
+	if (test_and_clear_bit(bit, &congested->state))
+		atomic_dec(&nr_wb_congested[sync]);
+	smp_mb__after_atomic();
+	if (waitqueue_active(wqh))
+		wake_up(wqh);
+}
+EXPORT_SYMBOL(clear_wb_congested);
+
+void set_wb_congested(struct bdi_writeback_congested *congested, int sync)
+{
+	enum wb_congested_state bit;
+
+	bit = sync ? WB_sync_congested : WB_async_congested;
+	if (!test_and_set_bit(bit, &congested->state))
+		atomic_inc(&nr_wb_congested[sync]);
+}
+EXPORT_SYMBOL(set_wb_congested);
+
+/**
+ * congestion_wait - wait for a backing_dev to become uncongested
+ * @sync: SYNC or ASYNC IO
+ * @timeout: timeout in jiffies
+ *
+ * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
+ * write congestion.  If no backing_devs are congested then just wait for the
+ * next write to be completed.
+ */
+long congestion_wait(int sync, long timeout)
+{
+	long ret;
+	unsigned long start = jiffies;
+	DEFINE_WAIT(wait);
+	wait_queue_head_t *wqh = &congestion_wqh[sync];
+
+	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+	ret = io_schedule_timeout(timeout);
+	finish_wait(wqh, &wait);
+
+	trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
+					jiffies_to_usecs(jiffies - start));
+
+	return ret;
+}
+EXPORT_SYMBOL(congestion_wait);
+
+/**
+ * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes
+ * @sync: SYNC or ASYNC IO
+ * @timeout: timeout in jiffies
+ *
+ * In the event of a congested backing_dev (any backing_dev) this waits
+ * for up to @timeout jiffies for either a BDI to exit congestion of the
+ * given @sync queue or a write to complete.
+ *
+ * The return value is 0 if the sleep is for the full timeout. Otherwise,
+ * it is the number of jiffies that were still remaining when the function
+ * returned. return_value == timeout implies the function did not sleep.
+ */
+long wait_iff_congested(int sync, long timeout)
+{
+	long ret;
+	unsigned long start = jiffies;
+	DEFINE_WAIT(wait);
+	wait_queue_head_t *wqh = &congestion_wqh[sync];
+
+	/*
+	 * If there is no congestion, yield if necessary instead
+	 * of sleeping on the congestion queue
+	 */
+	if (atomic_read(&nr_wb_congested[sync]) == 0) {
+		cond_resched();
+
+		/* In case we scheduled, work out time remaining */
+		ret = timeout - (jiffies - start);
+		if (ret < 0)
+			ret = 0;
+
+		goto out;
+	}
+
+	/* Sleep until uncongested or a write happens */
+	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+	ret = io_schedule_timeout(timeout);
+	finish_wait(wqh, &wait);
+
+out:
+	trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
+					jiffies_to_usecs(jiffies - start));
+
+	return ret;
+}
+EXPORT_SYMBOL(wait_iff_congested);