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TOMOYO Linux Cross Reference
Linux/include/linux/writeback.h

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 /*
  3  * include/linux/writeback.h
  4  */
  5 #ifndef WRITEBACK_H
  6 #define WRITEBACK_H
  7 
  8 #include <linux/sched.h>
  9 #include <linux/workqueue.h>
 10 #include <linux/fs.h>
 11 #include <linux/flex_proportions.h>
 12 #include <linux/backing-dev-defs.h>
 13 #include <linux/blk_types.h>
 14 
 15 struct bio;
 16 
 17 DECLARE_PER_CPU(int, dirty_throttle_leaks);
 18 
 19 /*
 20  * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
 21  *
 22  *      (thresh - thresh/DIRTY_FULL_SCOPE, thresh)
 23  *
 24  * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
 25  * time) for the dirty pages to drop, unless written enough pages.
 26  *
 27  * The global dirty threshold is normally equal to the global dirty limit,
 28  * except when the system suddenly allocates a lot of anonymous memory and
 29  * knocks down the global dirty threshold quickly, in which case the global
 30  * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
 31  */
 32 #define DIRTY_SCOPE             8
 33 #define DIRTY_FULL_SCOPE        (DIRTY_SCOPE / 2)
 34 
 35 struct backing_dev_info;
 36 
 37 /*
 38  * fs/fs-writeback.c
 39  */
 40 enum writeback_sync_modes {
 41         WB_SYNC_NONE,   /* Don't wait on anything */
 42         WB_SYNC_ALL,    /* Wait on every mapping */
 43 };
 44 
 45 /*
 46  * A control structure which tells the writeback code what to do.  These are
 47  * always on the stack, and hence need no locking.  They are always initialised
 48  * in a manner such that unspecified fields are set to zero.
 49  */
 50 struct writeback_control {
 51         long nr_to_write;               /* Write this many pages, and decrement
 52                                            this for each page written */
 53         long pages_skipped;             /* Pages which were not written */
 54 
 55         /*
 56          * For a_ops->writepages(): if start or end are non-zero then this is
 57          * a hint that the filesystem need only write out the pages inside that
 58          * byterange.  The byte at `end' is included in the writeout request.
 59          */
 60         loff_t range_start;
 61         loff_t range_end;
 62 
 63         enum writeback_sync_modes sync_mode;
 64 
 65         unsigned for_kupdate:1;         /* A kupdate writeback */
 66         unsigned for_background:1;      /* A background writeback */
 67         unsigned tagged_writepages:1;   /* tag-and-write to avoid livelock */
 68         unsigned for_reclaim:1;         /* Invoked from the page allocator */
 69         unsigned range_cyclic:1;        /* range_start is cyclic */
 70         unsigned for_sync:1;            /* sync(2) WB_SYNC_ALL writeback */
 71 #ifdef CONFIG_CGROUP_WRITEBACK
 72         struct bdi_writeback *wb;       /* wb this writeback is issued under */
 73         struct inode *inode;            /* inode being written out */
 74 
 75         /* foreign inode detection, see wbc_detach_inode() */
 76         int wb_id;                      /* current wb id */
 77         int wb_lcand_id;                /* last foreign candidate wb id */
 78         int wb_tcand_id;                /* this foreign candidate wb id */
 79         size_t wb_bytes;                /* bytes written by current wb */
 80         size_t wb_lcand_bytes;          /* bytes written by last candidate */
 81         size_t wb_tcand_bytes;          /* bytes written by this candidate */
 82 #endif
 83 };
 84 
 85 static inline int wbc_to_write_flags(struct writeback_control *wbc)
 86 {
 87         if (wbc->sync_mode == WB_SYNC_ALL)
 88                 return REQ_SYNC;
 89         else if (wbc->for_kupdate || wbc->for_background)
 90                 return REQ_BACKGROUND;
 91 
 92         return 0;
 93 }
 94 
 95 /*
 96  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
 97  * and are measured against each other in.  There always is one global
 98  * domain, global_wb_domain, that every wb in the system is a member of.
 99  * This allows measuring the relative bandwidth of each wb to distribute
100  * dirtyable memory accordingly.
101  */
102 struct wb_domain {
103         spinlock_t lock;
104 
105         /*
106          * Scale the writeback cache size proportional to the relative
107          * writeout speed.
108          *
109          * We do this by keeping a floating proportion between BDIs, based
110          * on page writeback completions [end_page_writeback()]. Those
111          * devices that write out pages fastest will get the larger share,
112          * while the slower will get a smaller share.
113          *
114          * We use page writeout completions because we are interested in
115          * getting rid of dirty pages. Having them written out is the
116          * primary goal.
117          *
118          * We introduce a concept of time, a period over which we measure
119          * these events, because demand can/will vary over time. The length
120          * of this period itself is measured in page writeback completions.
121          */
122         struct fprop_global completions;
123         struct timer_list period_timer; /* timer for aging of completions */
124         unsigned long period_time;
125 
126         /*
127          * The dirtyable memory and dirty threshold could be suddenly
128          * knocked down by a large amount (eg. on the startup of KVM in a
129          * swapless system). This may throw the system into deep dirty
130          * exceeded state and throttle heavy/light dirtiers alike. To
131          * retain good responsiveness, maintain global_dirty_limit for
132          * tracking slowly down to the knocked down dirty threshold.
133          *
134          * Both fields are protected by ->lock.
135          */
136         unsigned long dirty_limit_tstamp;
137         unsigned long dirty_limit;
138 };
139 
140 /**
141  * wb_domain_size_changed - memory available to a wb_domain has changed
142  * @dom: wb_domain of interest
143  *
144  * This function should be called when the amount of memory available to
145  * @dom has changed.  It resets @dom's dirty limit parameters to prevent
146  * the past values which don't match the current configuration from skewing
147  * dirty throttling.  Without this, when memory size of a wb_domain is
148  * greatly reduced, the dirty throttling logic may allow too many pages to
149  * be dirtied leading to consecutive unnecessary OOMs and may get stuck in
150  * that situation.
151  */
152 static inline void wb_domain_size_changed(struct wb_domain *dom)
153 {
154         spin_lock(&dom->lock);
155         dom->dirty_limit_tstamp = jiffies;
156         dom->dirty_limit = 0;
157         spin_unlock(&dom->lock);
158 }
159 
160 /*
161  * fs/fs-writeback.c
162  */     
163 struct bdi_writeback;
164 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
165 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
166                                                         enum wb_reason reason);
167 void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason);
168 void sync_inodes_sb(struct super_block *);
169 void wakeup_flusher_threads(enum wb_reason reason);
170 void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
171                                 enum wb_reason reason);
172 void inode_wait_for_writeback(struct inode *inode);
173 
174 /* writeback.h requires fs.h; it, too, is not included from here. */
175 static inline void wait_on_inode(struct inode *inode)
176 {
177         might_sleep();
178         wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
179 }
180 
181 #ifdef CONFIG_CGROUP_WRITEBACK
182 
183 #include <linux/cgroup.h>
184 #include <linux/bio.h>
185 
186 void __inode_attach_wb(struct inode *inode, struct page *page);
187 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
188                                  struct inode *inode)
189         __releases(&inode->i_lock);
190 void wbc_detach_inode(struct writeback_control *wbc);
191 void wbc_account_io(struct writeback_control *wbc, struct page *page,
192                     size_t bytes);
193 void cgroup_writeback_umount(void);
194 
195 /**
196  * inode_attach_wb - associate an inode with its wb
197  * @inode: inode of interest
198  * @page: page being dirtied (may be NULL)
199  *
200  * If @inode doesn't have its wb, associate it with the wb matching the
201  * memcg of @page or, if @page is NULL, %current.  May be called w/ or w/o
202  * @inode->i_lock.
203  */
204 static inline void inode_attach_wb(struct inode *inode, struct page *page)
205 {
206         if (!inode->i_wb)
207                 __inode_attach_wb(inode, page);
208 }
209 
210 /**
211  * inode_detach_wb - disassociate an inode from its wb
212  * @inode: inode of interest
213  *
214  * @inode is being freed.  Detach from its wb.
215  */
216 static inline void inode_detach_wb(struct inode *inode)
217 {
218         if (inode->i_wb) {
219                 WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
220                 wb_put(inode->i_wb);
221                 inode->i_wb = NULL;
222         }
223 }
224 
225 /**
226  * wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
227  * @wbc: writeback_control of interest
228  * @inode: target inode
229  *
230  * This function is to be used by __filemap_fdatawrite_range(), which is an
231  * alternative entry point into writeback code, and first ensures @inode is
232  * associated with a bdi_writeback and attaches it to @wbc.
233  */
234 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
235                                                struct inode *inode)
236 {
237         spin_lock(&inode->i_lock);
238         inode_attach_wb(inode, NULL);
239         wbc_attach_and_unlock_inode(wbc, inode);
240 }
241 
242 /**
243  * wbc_init_bio - writeback specific initializtion of bio
244  * @wbc: writeback_control for the writeback in progress
245  * @bio: bio to be initialized
246  *
247  * @bio is a part of the writeback in progress controlled by @wbc.  Perform
248  * writeback specific initialization.  This is used to apply the cgroup
249  * writeback context.  Must be called after the bio has been associated with
250  * a device.
251  */
252 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
253 {
254         /*
255          * pageout() path doesn't attach @wbc to the inode being written
256          * out.  This is intentional as we don't want the function to block
257          * behind a slow cgroup.  Ultimately, we want pageout() to kick off
258          * regular writeback instead of writing things out itself.
259          */
260         if (wbc->wb)
261                 bio_associate_blkg_from_css(bio, wbc->wb->blkcg_css);
262 }
263 
264 #else   /* CONFIG_CGROUP_WRITEBACK */
265 
266 static inline void inode_attach_wb(struct inode *inode, struct page *page)
267 {
268 }
269 
270 static inline void inode_detach_wb(struct inode *inode)
271 {
272 }
273 
274 static inline void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
275                                                struct inode *inode)
276         __releases(&inode->i_lock)
277 {
278         spin_unlock(&inode->i_lock);
279 }
280 
281 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
282                                                struct inode *inode)
283 {
284 }
285 
286 static inline void wbc_detach_inode(struct writeback_control *wbc)
287 {
288 }
289 
290 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
291 {
292 }
293 
294 static inline void wbc_account_io(struct writeback_control *wbc,
295                                   struct page *page, size_t bytes)
296 {
297 }
298 
299 static inline void cgroup_writeback_umount(void)
300 {
301 }
302 
303 #endif  /* CONFIG_CGROUP_WRITEBACK */
304 
305 /*
306  * mm/page-writeback.c
307  */
308 #ifdef CONFIG_BLOCK
309 void laptop_io_completion(struct backing_dev_info *info);
310 void laptop_sync_completion(void);
311 void laptop_mode_sync(struct work_struct *work);
312 void laptop_mode_timer_fn(struct timer_list *t);
313 #else
314 static inline void laptop_sync_completion(void) { }
315 #endif
316 bool node_dirty_ok(struct pglist_data *pgdat);
317 int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
318 #ifdef CONFIG_CGROUP_WRITEBACK
319 void wb_domain_exit(struct wb_domain *dom);
320 #endif
321 
322 extern struct wb_domain global_wb_domain;
323 
324 /* These are exported to sysctl. */
325 extern int dirty_background_ratio;
326 extern unsigned long dirty_background_bytes;
327 extern int vm_dirty_ratio;
328 extern unsigned long vm_dirty_bytes;
329 extern unsigned int dirty_writeback_interval;
330 extern unsigned int dirty_expire_interval;
331 extern unsigned int dirtytime_expire_interval;
332 extern int vm_highmem_is_dirtyable;
333 extern int block_dump;
334 extern int laptop_mode;
335 
336 extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
337                 void __user *buffer, size_t *lenp,
338                 loff_t *ppos);
339 extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
340                 void __user *buffer, size_t *lenp,
341                 loff_t *ppos);
342 extern int dirty_ratio_handler(struct ctl_table *table, int write,
343                 void __user *buffer, size_t *lenp,
344                 loff_t *ppos);
345 extern int dirty_bytes_handler(struct ctl_table *table, int write,
346                 void __user *buffer, size_t *lenp,
347                 loff_t *ppos);
348 int dirtytime_interval_handler(struct ctl_table *table, int write,
349                                void __user *buffer, size_t *lenp, loff_t *ppos);
350 
351 struct ctl_table;
352 int dirty_writeback_centisecs_handler(struct ctl_table *, int,
353                                       void __user *, size_t *, loff_t *);
354 
355 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
356 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
357 
358 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
359 void balance_dirty_pages_ratelimited(struct address_space *mapping);
360 bool wb_over_bg_thresh(struct bdi_writeback *wb);
361 
362 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
363                                 void *data);
364 
365 int generic_writepages(struct address_space *mapping,
366                        struct writeback_control *wbc);
367 void tag_pages_for_writeback(struct address_space *mapping,
368                              pgoff_t start, pgoff_t end);
369 int write_cache_pages(struct address_space *mapping,
370                       struct writeback_control *wbc, writepage_t writepage,
371                       void *data);
372 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
373 void writeback_set_ratelimit(void);
374 void tag_pages_for_writeback(struct address_space *mapping,
375                              pgoff_t start, pgoff_t end);
376 
377 void account_page_redirty(struct page *page);
378 
379 void sb_mark_inode_writeback(struct inode *inode);
380 void sb_clear_inode_writeback(struct inode *inode);
381 
382 #endif          /* WRITEBACK_H */
383 

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