diff --git a/include/linux/writeback.h b/include/linux/writeback.h
new file mode 100644
index 0000000..fdfd04e
--- /dev/null
+++ b/include/linux/writeback.h
@@ -0,0 +1,381 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * include/linux/writeback.h
+ */
+#ifndef WRITEBACK_H
+#define WRITEBACK_H
+
+#include <linux/sched.h>
+#include <linux/workqueue.h>
+#include <linux/fs.h>
+#include <linux/flex_proportions.h>
+#include <linux/backing-dev-defs.h>
+#include <linux/blk_types.h>
+
+struct bio;
+
+DECLARE_PER_CPU(int, dirty_throttle_leaks);
+
+/*
+ * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
+ *
+ *	(thresh - thresh/DIRTY_FULL_SCOPE, thresh)
+ *
+ * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
+ * time) for the dirty pages to drop, unless written enough pages.
+ *
+ * The global dirty threshold is normally equal to the global dirty limit,
+ * except when the system suddenly allocates a lot of anonymous memory and
+ * knocks down the global dirty threshold quickly, in which case the global
+ * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
+ */
+#define DIRTY_SCOPE		8
+#define DIRTY_FULL_SCOPE	(DIRTY_SCOPE / 2)
+
+struct backing_dev_info;
+
+/*
+ * fs/fs-writeback.c
+ */
+enum writeback_sync_modes {
+	WB_SYNC_NONE,	/* Don't wait on anything */
+	WB_SYNC_ALL,	/* Wait on every mapping */
+};
+
+/*
+ * A control structure which tells the writeback code what to do.  These are
+ * always on the stack, and hence need no locking.  They are always initialised
+ * in a manner such that unspecified fields are set to zero.
+ */
+struct writeback_control {
+	long nr_to_write;		/* Write this many pages, and decrement
+					   this for each page written */
+	long pages_skipped;		/* Pages which were not written */
+
+	/*
+	 * For a_ops->writepages(): if start or end are non-zero then this is
+	 * a hint that the filesystem need only write out the pages inside that
+	 * byterange.  The byte at `end' is included in the writeout request.
+	 */
+	loff_t range_start;
+	loff_t range_end;
+
+	enum writeback_sync_modes sync_mode;
+
+	unsigned for_kupdate:1;		/* A kupdate writeback */
+	unsigned for_background:1;	/* A background writeback */
+	unsigned tagged_writepages:1;	/* tag-and-write to avoid livelock */
+	unsigned for_reclaim:1;		/* Invoked from the page allocator */
+	unsigned range_cyclic:1;	/* range_start is cyclic */
+	unsigned for_sync:1;		/* sync(2) WB_SYNC_ALL writeback */
+#ifdef CONFIG_CGROUP_WRITEBACK
+	struct bdi_writeback *wb;	/* wb this writeback is issued under */
+	struct inode *inode;		/* inode being written out */
+
+	/* foreign inode detection, see wbc_detach_inode() */
+	int wb_id;			/* current wb id */
+	int wb_lcand_id;		/* last foreign candidate wb id */
+	int wb_tcand_id;		/* this foreign candidate wb id */
+	size_t wb_bytes;		/* bytes written by current wb */
+	size_t wb_lcand_bytes;		/* bytes written by last candidate */
+	size_t wb_tcand_bytes;		/* bytes written by this candidate */
+#endif
+};
+
+static inline int wbc_to_write_flags(struct writeback_control *wbc)
+{
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		return REQ_SYNC;
+	else if (wbc->for_kupdate || wbc->for_background)
+		return REQ_BACKGROUND;
+
+	return 0;
+}
+
+/*
+ * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
+ * and are measured against each other in.  There always is one global
+ * domain, global_wb_domain, that every wb in the system is a member of.
+ * This allows measuring the relative bandwidth of each wb to distribute
+ * dirtyable memory accordingly.
+ */
+struct wb_domain {
+	spinlock_t lock;
+
+	/*
+	 * Scale the writeback cache size proportional to the relative
+	 * writeout speed.
+	 *
+	 * We do this by keeping a floating proportion between BDIs, based
+	 * on page writeback completions [end_page_writeback()]. Those
+	 * devices that write out pages fastest will get the larger share,
+	 * while the slower will get a smaller share.
+	 *
+	 * We use page writeout completions because we are interested in
+	 * getting rid of dirty pages. Having them written out is the
+	 * primary goal.
+	 *
+	 * We introduce a concept of time, a period over which we measure
+	 * these events, because demand can/will vary over time. The length
+	 * of this period itself is measured in page writeback completions.
+	 */
+	struct fprop_global completions;
+	struct timer_list period_timer;	/* timer for aging of completions */
+	unsigned long period_time;
+
+	/*
+	 * The dirtyable memory and dirty threshold could be suddenly
+	 * knocked down by a large amount (eg. on the startup of KVM in a
+	 * swapless system). This may throw the system into deep dirty
+	 * exceeded state and throttle heavy/light dirtiers alike. To
+	 * retain good responsiveness, maintain global_dirty_limit for
+	 * tracking slowly down to the knocked down dirty threshold.
+	 *
+	 * Both fields are protected by ->lock.
+	 */
+	unsigned long dirty_limit_tstamp;
+	unsigned long dirty_limit;
+};
+
+/**
+ * wb_domain_size_changed - memory available to a wb_domain has changed
+ * @dom: wb_domain of interest
+ *
+ * This function should be called when the amount of memory available to
+ * @dom has changed.  It resets @dom's dirty limit parameters to prevent
+ * the past values which don't match the current configuration from skewing
+ * dirty throttling.  Without this, when memory size of a wb_domain is
+ * greatly reduced, the dirty throttling logic may allow too many pages to
+ * be dirtied leading to consecutive unnecessary OOMs and may get stuck in
+ * that situation.
+ */
+static inline void wb_domain_size_changed(struct wb_domain *dom)
+{
+	spin_lock(&dom->lock);
+	dom->dirty_limit_tstamp = jiffies;
+	dom->dirty_limit = 0;
+	spin_unlock(&dom->lock);
+}
+
+/*
+ * fs/fs-writeback.c
+ */	
+struct bdi_writeback;
+void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
+void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
+							enum wb_reason reason);
+void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason);
+void sync_inodes_sb(struct super_block *);
+void wakeup_flusher_threads(enum wb_reason reason);
+void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
+				enum wb_reason reason);
+void inode_wait_for_writeback(struct inode *inode);
+
+/* writeback.h requires fs.h; it, too, is not included from here. */
+static inline void wait_on_inode(struct inode *inode)
+{
+	might_sleep();
+	wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
+}
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+
+#include <linux/cgroup.h>
+#include <linux/bio.h>
+
+void __inode_attach_wb(struct inode *inode, struct page *page);
+void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
+				 struct inode *inode)
+	__releases(&inode->i_lock);
+void wbc_detach_inode(struct writeback_control *wbc);
+void wbc_account_io(struct writeback_control *wbc, struct page *page,
+		    size_t bytes);
+void cgroup_writeback_umount(void);
+
+/**
+ * inode_attach_wb - associate an inode with its wb
+ * @inode: inode of interest
+ * @page: page being dirtied (may be NULL)
+ *
+ * If @inode doesn't have its wb, associate it with the wb matching the
+ * memcg of @page or, if @page is NULL, %current.  May be called w/ or w/o
+ * @inode->i_lock.
+ */
+static inline void inode_attach_wb(struct inode *inode, struct page *page)
+{
+	if (!inode->i_wb)
+		__inode_attach_wb(inode, page);
+}
+
+/**
+ * inode_detach_wb - disassociate an inode from its wb
+ * @inode: inode of interest
+ *
+ * @inode is being freed.  Detach from its wb.
+ */
+static inline void inode_detach_wb(struct inode *inode)
+{
+	if (inode->i_wb) {
+		WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
+		wb_put(inode->i_wb);
+		inode->i_wb = NULL;
+	}
+}
+
+/**
+ * wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
+ * @wbc: writeback_control of interest
+ * @inode: target inode
+ *
+ * This function is to be used by __filemap_fdatawrite_range(), which is an
+ * alternative entry point into writeback code, and first ensures @inode is
+ * associated with a bdi_writeback and attaches it to @wbc.
+ */
+static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
+					       struct inode *inode)
+{
+	spin_lock(&inode->i_lock);
+	inode_attach_wb(inode, NULL);
+	wbc_attach_and_unlock_inode(wbc, inode);
+}
+
+/**
+ * wbc_init_bio - writeback specific initializtion of bio
+ * @wbc: writeback_control for the writeback in progress
+ * @bio: bio to be initialized
+ *
+ * @bio is a part of the writeback in progress controlled by @wbc.  Perform
+ * writeback specific initialization.  This is used to apply the cgroup
+ * writeback context.
+ */
+static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
+{
+	/*
+	 * pageout() path doesn't attach @wbc to the inode being written
+	 * out.  This is intentional as we don't want the function to block
+	 * behind a slow cgroup.  Ultimately, we want pageout() to kick off
+	 * regular writeback instead of writing things out itself.
+	 */
+	if (wbc->wb)
+		bio_associate_blkcg(bio, wbc->wb->blkcg_css);
+}
+
+#else	/* CONFIG_CGROUP_WRITEBACK */
+
+static inline void inode_attach_wb(struct inode *inode, struct page *page)
+{
+}
+
+static inline void inode_detach_wb(struct inode *inode)
+{
+}
+
+static inline void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
+					       struct inode *inode)
+	__releases(&inode->i_lock)
+{
+	spin_unlock(&inode->i_lock);
+}
+
+static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
+					       struct inode *inode)
+{
+}
+
+static inline void wbc_detach_inode(struct writeback_control *wbc)
+{
+}
+
+static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
+{
+}
+
+static inline void wbc_account_io(struct writeback_control *wbc,
+				  struct page *page, size_t bytes)
+{
+}
+
+static inline void cgroup_writeback_umount(void)
+{
+}
+
+#endif	/* CONFIG_CGROUP_WRITEBACK */
+
+/*
+ * mm/page-writeback.c
+ */
+#ifdef CONFIG_BLOCK
+void laptop_io_completion(struct backing_dev_info *info);
+void laptop_sync_completion(void);
+void laptop_mode_sync(struct work_struct *work);
+void laptop_mode_timer_fn(struct timer_list *t);
+#else
+static inline void laptop_sync_completion(void) { }
+#endif
+bool node_dirty_ok(struct pglist_data *pgdat);
+int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
+#ifdef CONFIG_CGROUP_WRITEBACK
+void wb_domain_exit(struct wb_domain *dom);
+#endif
+
+extern struct wb_domain global_wb_domain;
+
+/* These are exported to sysctl. */
+extern int dirty_background_ratio;
+extern unsigned long dirty_background_bytes;
+extern int vm_dirty_ratio;
+extern unsigned long vm_dirty_bytes;
+extern unsigned int dirty_writeback_interval;
+extern unsigned int dirty_expire_interval;
+extern unsigned int dirtytime_expire_interval;
+extern int vm_highmem_is_dirtyable;
+extern int block_dump;
+extern int laptop_mode;
+
+extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+extern int dirty_ratio_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+extern int dirty_bytes_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+int dirtytime_interval_handler(struct ctl_table *table, int write,
+			       void __user *buffer, size_t *lenp, loff_t *ppos);
+
+struct ctl_table;
+int dirty_writeback_centisecs_handler(struct ctl_table *, int,
+				      void __user *, size_t *, loff_t *);
+
+void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
+unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
+
+void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
+void balance_dirty_pages_ratelimited(struct address_space *mapping);
+bool wb_over_bg_thresh(struct bdi_writeback *wb);
+
+typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
+				void *data);
+
+int generic_writepages(struct address_space *mapping,
+		       struct writeback_control *wbc);
+void tag_pages_for_writeback(struct address_space *mapping,
+			     pgoff_t start, pgoff_t end);
+int write_cache_pages(struct address_space *mapping,
+		      struct writeback_control *wbc, writepage_t writepage,
+		      void *data);
+int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
+void writeback_set_ratelimit(void);
+void tag_pages_for_writeback(struct address_space *mapping,
+			     pgoff_t start, pgoff_t end);
+
+void account_page_redirty(struct page *page);
+
+void sb_mark_inode_writeback(struct inode *inode);
+void sb_clear_inode_writeback(struct inode *inode);
+
+#endif		/* WRITEBACK_H */