text: /* 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);
  void inode_io_list_del(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,
  			   enum wb_reason reason, struct wb_completion *done);
  void cgroup_writeback_umount(void);
  bool cleanup_offline_cgwb(struct bdi_writeback *wb);
  
  /**
   * 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
   */
  void laptop_io_completion(struct backing_dev_info *info);
  void laptop_sync_completion(void);
  void laptop_mode_timer_fn(struct timer_list *t);
  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 laptop_mode;
  
  int dirty_background_ratio_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  int dirty_background_bytes_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  int dirty_ratio_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  int dirty_bytes_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  int dirtytime_interval_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
  		void *buffer, size_t *lenp, loff_t *ppos);
  
  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);
  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 */
  