diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
new file mode 100644
index 0000000..9a6bc09
--- /dev/null
+++ b/include/linux/backing-dev-defs.h
@@ -0,0 +1,298 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_BACKING_DEV_DEFS_H
+#define __LINUX_BACKING_DEV_DEFS_H
+
+#include <linux/list.h>
+#include <linux/radix-tree.h>
+#include <linux/rbtree.h>
+#include <linux/spinlock.h>
+#include <linux/percpu_counter.h>
+#include <linux/percpu-refcount.h>
+#include <linux/flex_proportions.h>
+#include <linux/timer.h>
+#include <linux/workqueue.h>
+#include <linux/kref.h>
+#include <linux/refcount.h>
+
+struct page;
+struct device;
+struct dentry;
+
+/*
+ * Bits in bdi_writeback.state
+ */
+enum wb_state {
+	WB_registered,		/* bdi_register() was done */
+	WB_writeback_running,	/* Writeback is in progress */
+	WB_has_dirty_io,	/* Dirty inodes on ->b_{dirty|io|more_io} */
+	WB_start_all,		/* nr_pages == 0 (all) work pending */
+};
+
+enum wb_congested_state {
+	WB_async_congested,	/* The async (write) queue is getting full */
+	WB_sync_congested,	/* The sync queue is getting full */
+};
+
+typedef int (congested_fn)(void *, int);
+
+enum wb_stat_item {
+	WB_RECLAIMABLE,
+	WB_WRITEBACK,
+	WB_DIRTIED,
+	WB_WRITTEN,
+	NR_WB_STAT_ITEMS
+};
+
+#define WB_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
+
+/*
+ * why some writeback work was initiated
+ */
+enum wb_reason {
+	WB_REASON_BACKGROUND,
+	WB_REASON_VMSCAN,
+	WB_REASON_SYNC,
+	WB_REASON_PERIODIC,
+	WB_REASON_LAPTOP_TIMER,
+	WB_REASON_FREE_MORE_MEM,
+	WB_REASON_FS_FREE_SPACE,
+	/*
+	 * There is no bdi forker thread any more and works are done
+	 * by emergency worker, however, this is TPs userland visible
+	 * and we'll be exposing exactly the same information,
+	 * so it has a mismatch name.
+	 */
+	WB_REASON_FORKER_THREAD,
+
+	WB_REASON_MAX,
+};
+
+/*
+ * For cgroup writeback, multiple wb's may map to the same blkcg.  Those
+ * wb's can operate mostly independently but should share the congested
+ * state.  To facilitate such sharing, the congested state is tracked using
+ * the following struct which is created on demand, indexed by blkcg ID on
+ * its bdi, and refcounted.
+ */
+struct bdi_writeback_congested {
+	unsigned long state;		/* WB_[a]sync_congested flags */
+	refcount_t refcnt;		/* nr of attached wb's and blkg */
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+	struct backing_dev_info *__bdi;	/* the associated bdi, set to NULL
+					 * on bdi unregistration. For memcg-wb
+					 * internal use only! */
+	int blkcg_id;			/* ID of the associated blkcg */
+	struct rb_node rb_node;		/* on bdi->cgwb_congestion_tree */
+#endif
+};
+
+/*
+ * Each wb (bdi_writeback) can perform writeback operations, is measured
+ * and throttled, independently.  Without cgroup writeback, each bdi
+ * (bdi_writeback) is served by its embedded bdi->wb.
+ *
+ * On the default hierarchy, blkcg implicitly enables memcg.  This allows
+ * using memcg's page ownership for attributing writeback IOs, and every
+ * memcg - blkcg combination can be served by its own wb by assigning a
+ * dedicated wb to each memcg, which enables isolation across different
+ * cgroups and propagation of IO back pressure down from the IO layer upto
+ * the tasks which are generating the dirty pages to be written back.
+ *
+ * A cgroup wb is indexed on its bdi by the ID of the associated memcg,
+ * refcounted with the number of inodes attached to it, and pins the memcg
+ * and the corresponding blkcg.  As the corresponding blkcg for a memcg may
+ * change as blkcg is disabled and enabled higher up in the hierarchy, a wb
+ * is tested for blkcg after lookup and removed from index on mismatch so
+ * that a new wb for the combination can be created.
+ */
+struct bdi_writeback {
+	struct backing_dev_info *bdi;	/* our parent bdi */
+
+	unsigned long state;		/* Always use atomic bitops on this */
+	unsigned long last_old_flush;	/* last old data flush */
+
+	struct list_head b_dirty;	/* dirty inodes */
+	struct list_head b_io;		/* parked for writeback */
+	struct list_head b_more_io;	/* parked for more writeback */
+	struct list_head b_dirty_time;	/* time stamps are dirty */
+	spinlock_t list_lock;		/* protects the b_* lists */
+
+	struct percpu_counter stat[NR_WB_STAT_ITEMS];
+
+	struct bdi_writeback_congested *congested;
+
+	unsigned long bw_time_stamp;	/* last time write bw is updated */
+	unsigned long dirtied_stamp;
+	unsigned long written_stamp;	/* pages written at bw_time_stamp */
+	unsigned long write_bandwidth;	/* the estimated write bandwidth */
+	unsigned long avg_write_bandwidth; /* further smoothed write bw, > 0 */
+
+	/*
+	 * The base dirty throttle rate, re-calculated on every 200ms.
+	 * All the bdi tasks' dirty rate will be curbed under it.
+	 * @dirty_ratelimit tracks the estimated @balanced_dirty_ratelimit
+	 * in small steps and is much more smooth/stable than the latter.
+	 */
+	unsigned long dirty_ratelimit;
+	unsigned long balanced_dirty_ratelimit;
+
+	struct fprop_local_percpu completions;
+	int dirty_exceeded;
+	enum wb_reason start_all_reason;
+
+	spinlock_t work_lock;		/* protects work_list & dwork scheduling */
+	struct list_head work_list;
+	struct delayed_work dwork;	/* work item used for writeback */
+
+	unsigned long dirty_sleep;	/* last wait */
+
+	struct list_head bdi_node;	/* anchored at bdi->wb_list */
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+	struct percpu_ref refcnt;	/* used only for !root wb's */
+	struct fprop_local_percpu memcg_completions;
+	struct cgroup_subsys_state *memcg_css; /* the associated memcg */
+	struct cgroup_subsys_state *blkcg_css; /* and blkcg */
+	struct list_head memcg_node;	/* anchored at memcg->cgwb_list */
+	struct list_head blkcg_node;	/* anchored at blkcg->cgwb_list */
+
+	union {
+		struct work_struct release_work;
+		struct rcu_head rcu;
+	};
+#endif
+};
+
+struct backing_dev_info {
+	struct list_head bdi_list;
+	unsigned long ra_pages;	/* max readahead in PAGE_SIZE units */
+	unsigned long io_pages;	/* max allowed IO size */
+	congested_fn *congested_fn; /* Function pointer if device is md/dm */
+	void *congested_data;	/* Pointer to aux data for congested func */
+
+	const char *name;
+
+	struct kref refcnt;	/* Reference counter for the structure */
+	unsigned int capabilities; /* Device capabilities */
+	unsigned int min_ratio;
+	unsigned int max_ratio, max_prop_frac;
+
+	/*
+	 * Sum of avg_write_bw of wbs with dirty inodes.  > 0 if there are
+	 * any dirty wbs, which is depended upon by bdi_has_dirty().
+	 */
+	atomic_long_t tot_write_bandwidth;
+
+	struct bdi_writeback wb;  /* the root writeback info for this bdi */
+	struct list_head wb_list; /* list of all wbs */
+#ifdef CONFIG_CGROUP_WRITEBACK
+	struct radix_tree_root cgwb_tree; /* radix tree of active cgroup wbs */
+	struct rb_root cgwb_congested_tree; /* their congested states */
+	struct mutex cgwb_release_mutex;  /* protect shutdown of wb structs */
+#else
+	struct bdi_writeback_congested *wb_congested;
+#endif
+	wait_queue_head_t wb_waitq;
+
+	struct device *dev;
+	struct device *owner;
+
+	struct timer_list laptop_mode_wb_timer;
+
+#ifdef CONFIG_DEBUG_FS
+	struct dentry *debug_dir;
+	struct dentry *debug_stats;
+#endif
+};
+
+enum {
+	BLK_RW_ASYNC	= 0,
+	BLK_RW_SYNC	= 1,
+};
+
+void clear_wb_congested(struct bdi_writeback_congested *congested, int sync);
+void set_wb_congested(struct bdi_writeback_congested *congested, int sync);
+
+static inline void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
+{
+	clear_wb_congested(bdi->wb.congested, sync);
+}
+
+static inline void set_bdi_congested(struct backing_dev_info *bdi, int sync)
+{
+	set_wb_congested(bdi->wb.congested, sync);
+}
+
+struct wb_lock_cookie {
+	bool locked;
+	unsigned long flags;
+};
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+
+/**
+ * wb_tryget - try to increment a wb's refcount
+ * @wb: bdi_writeback to get
+ */
+static inline bool wb_tryget(struct bdi_writeback *wb)
+{
+	if (wb != &wb->bdi->wb)
+		return percpu_ref_tryget(&wb->refcnt);
+	return true;
+}
+
+/**
+ * wb_get - increment a wb's refcount
+ * @wb: bdi_writeback to get
+ */
+static inline void wb_get(struct bdi_writeback *wb)
+{
+	if (wb != &wb->bdi->wb)
+		percpu_ref_get(&wb->refcnt);
+}
+
+/**
+ * wb_put - decrement a wb's refcount
+ * @wb: bdi_writeback to put
+ */
+static inline void wb_put(struct bdi_writeback *wb)
+{
+	if (wb != &wb->bdi->wb)
+		percpu_ref_put(&wb->refcnt);
+}
+
+/**
+ * wb_dying - is a wb dying?
+ * @wb: bdi_writeback of interest
+ *
+ * Returns whether @wb is unlinked and being drained.
+ */
+static inline bool wb_dying(struct bdi_writeback *wb)
+{
+	return percpu_ref_is_dying(&wb->refcnt);
+}
+
+#else	/* CONFIG_CGROUP_WRITEBACK */
+
+static inline bool wb_tryget(struct bdi_writeback *wb)
+{
+	return true;
+}
+
+static inline void wb_get(struct bdi_writeback *wb)
+{
+}
+
+static inline void wb_put(struct bdi_writeback *wb)
+{
+}
+
+static inline bool wb_dying(struct bdi_writeback *wb)
+{
+	return false;
+}
+
+#endif	/* CONFIG_CGROUP_WRITEBACK */
+
+#endif	/* __LINUX_BACKING_DEV_DEFS_H */