include/linux/writeback.h - kernel/msm-5.4 - Gitiles

 /* 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>
 #include <linux/blk-cgroup.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 */

 	/*
 	 * When writeback IOs are bounced through async layers, only the
 	 * initial synchronous phase should be accounted towards inode
 	 * cgroup ownership arbitration to avoid confusion.  Later stages
 	 * can set the following flag to disable the accounting.
 	 */
 	unsigned no_cgroup_owner:1;

 	unsigned punt_to_cgroup:1;	/* cgrp punting, see __REQ_CGROUP_PUNT */

 #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)
 {
 	int flags = 0;

 	if (wbc->punt_to_cgroup)
 		flags = REQ_CGROUP_PUNT;

 	if (wbc->sync_mode == WB_SYNC_ALL)
 		flags |= REQ_SYNC;
 	else if (wbc->for_kupdate || wbc->for_background)
 		flags |= REQ_BACKGROUND;

 	return flags;
 }

 static inline struct cgroup_subsys_state *
 wbc_blkcg_css(struct writeback_control *wbc)
 {
 #ifdef CONFIG_CGROUP_WRITEBACK
 	if (wbc->wb)
 		return wbc->wb->blkcg_css;
 #endif
 	return blkcg_root_css;
 }

 /*
  * 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_cgroup_owner(struct writeback_control *wbc, struct page *page,
 			      size_t bytes);
 int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
 			   enum wb_reason reason, struct wb_completion *done);
 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.  Must be called after the bio has been associated with
  * a device.
  */
 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_blkg_from_css(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_cgroup_owner(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 */
	/* 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>
	#include <linux/blk-cgroup.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 */

	/*
	* When writeback IOs are bounced through async layers, only the
	* initial synchronous phase should be accounted towards inode
	* cgroup ownership arbitration to avoid confusion. Later stages
	* can set the following flag to disable the accounting.
	*/
	unsigned no_cgroup_owner:1;

	unsigned punt_to_cgroup:1; /* cgrp punting, see __REQ_CGROUP_PUNT */

	#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)
	{
	int flags = 0;

	if (wbc->punt_to_cgroup)
	flags = REQ_CGROUP_PUNT;

	if (wbc->sync_mode == WB_SYNC_ALL)
	flags \|= REQ_SYNC;
	else if (wbc->for_kupdate \|\| wbc->for_background)
	flags \|= REQ_BACKGROUND;

	return flags;
	}

	static inline struct cgroup_subsys_state *
	wbc_blkcg_css(struct writeback_control *wbc)
	{
	#ifdef CONFIG_CGROUP_WRITEBACK
	if (wbc->wb)
	return wbc->wb->blkcg_css;
	#endif
	return blkcg_root_css;
	}

	/*
	* 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_cgroup_owner(struct writeback_control wbc, struct page page,
	size_t bytes);
	int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
	enum wb_reason reason, struct wb_completion *done);
	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. Must be called after the bio has been associated with
	* a device.
	*/
	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_blkg_from_css(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_cgroup_owner(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 */