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

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  1 /*
  2  * include/linux/writeback.h
  3  */
  4 #ifndef WRITEBACK_H
  5 #define WRITEBACK_H
  6 
  7 #include <linux/sched.h>
  8 #include <linux/workqueue.h>
  9 #include <linux/fs.h>
 10 #include <linux/flex_proportions.h>
 11 #include <linux/backing-dev-defs.h>
 12 
 13 DECLARE_PER_CPU(int, dirty_throttle_leaks);
 14 
 15 /*
 16  * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
 17  *
 18  *      (thresh - thresh/DIRTY_FULL_SCOPE, thresh)
 19  *
 20  * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
 21  * time) for the dirty pages to drop, unless written enough pages.
 22  *
 23  * The global dirty threshold is normally equal to the global dirty limit,
 24  * except when the system suddenly allocates a lot of anonymous memory and
 25  * knocks down the global dirty threshold quickly, in which case the global
 26  * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
 27  */
 28 #define DIRTY_SCOPE             8
 29 #define DIRTY_FULL_SCOPE        (DIRTY_SCOPE / 2)
 30 
 31 struct backing_dev_info;
 32 
 33 /*
 34  * fs/fs-writeback.c
 35  */
 36 enum writeback_sync_modes {
 37         WB_SYNC_NONE,   /* Don't wait on anything */
 38         WB_SYNC_ALL,    /* Wait on every mapping */
 39 };
 40 
 41 /*
 42  * why some writeback work was initiated
 43  */
 44 enum wb_reason {
 45         WB_REASON_BACKGROUND,
 46         WB_REASON_TRY_TO_FREE_PAGES,
 47         WB_REASON_SYNC,
 48         WB_REASON_PERIODIC,
 49         WB_REASON_LAPTOP_TIMER,
 50         WB_REASON_FREE_MORE_MEM,
 51         WB_REASON_FS_FREE_SPACE,
 52         /*
 53          * There is no bdi forker thread any more and works are done
 54          * by emergency worker, however, this is TPs userland visible
 55          * and we'll be exposing exactly the same information,
 56          * so it has a mismatch name.
 57          */
 58         WB_REASON_FORKER_THREAD,
 59 
 60         WB_REASON_MAX,
 61 };
 62 
 63 /*
 64  * A control structure which tells the writeback code what to do.  These are
 65  * always on the stack, and hence need no locking.  They are always initialised
 66  * in a manner such that unspecified fields are set to zero.
 67  */
 68 struct writeback_control {
 69         long nr_to_write;               /* Write this many pages, and decrement
 70                                            this for each page written */
 71         long pages_skipped;             /* Pages which were not written */
 72 
 73         /*
 74          * For a_ops->writepages(): if start or end are non-zero then this is
 75          * a hint that the filesystem need only write out the pages inside that
 76          * byterange.  The byte at `end' is included in the writeout request.
 77          */
 78         loff_t range_start;
 79         loff_t range_end;
 80 
 81         enum writeback_sync_modes sync_mode;
 82 
 83         unsigned for_kupdate:1;         /* A kupdate writeback */
 84         unsigned for_background:1;      /* A background writeback */
 85         unsigned tagged_writepages:1;   /* tag-and-write to avoid livelock */
 86         unsigned for_reclaim:1;         /* Invoked from the page allocator */
 87         unsigned range_cyclic:1;        /* range_start is cyclic */
 88         unsigned for_sync:1;            /* sync(2) WB_SYNC_ALL writeback */
 89 #ifdef CONFIG_CGROUP_WRITEBACK
 90         struct bdi_writeback *wb;       /* wb this writeback is issued under */
 91         struct inode *inode;            /* inode being written out */
 92 
 93         /* foreign inode detection, see wbc_detach_inode() */
 94         int wb_id;                      /* current wb id */
 95         int wb_lcand_id;                /* last foreign candidate wb id */
 96         int wb_tcand_id;                /* this foreign candidate wb id */
 97         size_t wb_bytes;                /* bytes written by current wb */
 98         size_t wb_lcand_bytes;          /* bytes written by last candidate */
 99         size_t wb_tcand_bytes;          /* bytes written by this candidate */
100 #endif
101 };
102 
103 /*
104  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
105  * and are measured against each other in.  There always is one global
106  * domain, global_wb_domain, that every wb in the system is a member of.
107  * This allows measuring the relative bandwidth of each wb to distribute
108  * dirtyable memory accordingly.
109  */
110 struct wb_domain {
111         spinlock_t lock;
112 
113         /*
114          * Scale the writeback cache size proportional to the relative
115          * writeout speed.
116          *
117          * We do this by keeping a floating proportion between BDIs, based
118          * on page writeback completions [end_page_writeback()]. Those
119          * devices that write out pages fastest will get the larger share,
120          * while the slower will get a smaller share.
121          *
122          * We use page writeout completions because we are interested in
123          * getting rid of dirty pages. Having them written out is the
124          * primary goal.
125          *
126          * We introduce a concept of time, a period over which we measure
127          * these events, because demand can/will vary over time. The length
128          * of this period itself is measured in page writeback completions.
129          */
130         struct fprop_global completions;
131         struct timer_list period_timer; /* timer for aging of completions */
132         unsigned long period_time;
133 
134         /*
135          * The dirtyable memory and dirty threshold could be suddenly
136          * knocked down by a large amount (eg. on the startup of KVM in a
137          * swapless system). This may throw the system into deep dirty
138          * exceeded state and throttle heavy/light dirtiers alike. To
139          * retain good responsiveness, maintain global_dirty_limit for
140          * tracking slowly down to the knocked down dirty threshold.
141          *
142          * Both fields are protected by ->lock.
143          */
144         unsigned long dirty_limit_tstamp;
145         unsigned long dirty_limit;
146 };
147 
148 /**
149  * wb_domain_size_changed - memory available to a wb_domain has changed
150  * @dom: wb_domain of interest
151  *
152  * This function should be called when the amount of memory available to
153  * @dom has changed.  It resets @dom's dirty limit parameters to prevent
154  * the past values which don't match the current configuration from skewing
155  * dirty throttling.  Without this, when memory size of a wb_domain is
156  * greatly reduced, the dirty throttling logic may allow too many pages to
157  * be dirtied leading to consecutive unnecessary OOMs and may get stuck in
158  * that situation.
159  */
160 static inline void wb_domain_size_changed(struct wb_domain *dom)
161 {
162         spin_lock(&dom->lock);
163         dom->dirty_limit_tstamp = jiffies;
164         dom->dirty_limit = 0;
165         spin_unlock(&dom->lock);
166 }
167 
168 /*
169  * fs/fs-writeback.c
170  */     
171 struct bdi_writeback;
172 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
173 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
174                                                         enum wb_reason reason);
175 bool try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
176 bool try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
177                                    enum wb_reason reason);
178 void sync_inodes_sb(struct super_block *);
179 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
180 void inode_wait_for_writeback(struct inode *inode);
181 
182 /* writeback.h requires fs.h; it, too, is not included from here. */
183 static inline void wait_on_inode(struct inode *inode)
184 {
185         might_sleep();
186         wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
187 }
188 
189 #ifdef CONFIG_CGROUP_WRITEBACK
190 
191 #include <linux/cgroup.h>
192 #include <linux/bio.h>
193 
194 void __inode_attach_wb(struct inode *inode, struct page *page);
195 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
196                                  struct inode *inode)
197         __releases(&inode->i_lock);
198 void wbc_detach_inode(struct writeback_control *wbc);
199 void wbc_account_io(struct writeback_control *wbc, struct page *page,
200                     size_t bytes);
201 void cgroup_writeback_umount(void);
202 
203 /**
204  * inode_attach_wb - associate an inode with its wb
205  * @inode: inode of interest
206  * @page: page being dirtied (may be NULL)
207  *
208  * If @inode doesn't have its wb, associate it with the wb matching the
209  * memcg of @page or, if @page is NULL, %current.  May be called w/ or w/o
210  * @inode->i_lock.
211  */
212 static inline void inode_attach_wb(struct inode *inode, struct page *page)
213 {
214         if (!inode->i_wb)
215                 __inode_attach_wb(inode, page);
216 }
217 
218 /**
219  * inode_detach_wb - disassociate an inode from its wb
220  * @inode: inode of interest
221  *
222  * @inode is being freed.  Detach from its wb.
223  */
224 static inline void inode_detach_wb(struct inode *inode)
225 {
226         if (inode->i_wb) {
227                 wb_put(inode->i_wb);
228                 inode->i_wb = NULL;
229         }
230 }
231 
232 /**
233  * wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
234  * @wbc: writeback_control of interest
235  * @inode: target inode
236  *
237  * This function is to be used by __filemap_fdatawrite_range(), which is an
238  * alternative entry point into writeback code, and first ensures @inode is
239  * associated with a bdi_writeback and attaches it to @wbc.
240  */
241 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
242                                                struct inode *inode)
243 {
244         spin_lock(&inode->i_lock);
245         inode_attach_wb(inode, NULL);
246         wbc_attach_and_unlock_inode(wbc, inode);
247 }
248 
249 /**
250  * wbc_init_bio - writeback specific initializtion of bio
251  * @wbc: writeback_control for the writeback in progress
252  * @bio: bio to be initialized
253  *
254  * @bio is a part of the writeback in progress controlled by @wbc.  Perform
255  * writeback specific initialization.  This is used to apply the cgroup
256  * writeback context.
257  */
258 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
259 {
260         /*
261          * pageout() path doesn't attach @wbc to the inode being written
262          * out.  This is intentional as we don't want the function to block
263          * behind a slow cgroup.  Ultimately, we want pageout() to kick off
264          * regular writeback instead of writing things out itself.
265          */
266         if (wbc->wb)
267                 bio_associate_blkcg(bio, wbc->wb->blkcg_css);
268 }
269 
270 #else   /* CONFIG_CGROUP_WRITEBACK */
271 
272 static inline void inode_attach_wb(struct inode *inode, struct page *page)
273 {
274 }
275 
276 static inline void inode_detach_wb(struct inode *inode)
277 {
278 }
279 
280 static inline void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
281                                                struct inode *inode)
282         __releases(&inode->i_lock)
283 {
284         spin_unlock(&inode->i_lock);
285 }
286 
287 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
288                                                struct inode *inode)
289 {
290 }
291 
292 static inline void wbc_detach_inode(struct writeback_control *wbc)
293 {
294 }
295 
296 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
297 {
298 }
299 
300 static inline void wbc_account_io(struct writeback_control *wbc,
301                                   struct page *page, size_t bytes)
302 {
303 }
304 
305 static inline void cgroup_writeback_umount(void)
306 {
307 }
308 
309 #endif  /* CONFIG_CGROUP_WRITEBACK */
310 
311 /*
312  * mm/page-writeback.c
313  */
314 #ifdef CONFIG_BLOCK
315 void laptop_io_completion(struct backing_dev_info *info);
316 void laptop_sync_completion(void);
317 void laptop_mode_sync(struct work_struct *work);
318 void laptop_mode_timer_fn(unsigned long data);
319 #else
320 static inline void laptop_sync_completion(void) { }
321 #endif
322 void throttle_vm_writeout(gfp_t gfp_mask);
323 bool zone_dirty_ok(struct zone *zone);
324 int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
325 #ifdef CONFIG_CGROUP_WRITEBACK
326 void wb_domain_exit(struct wb_domain *dom);
327 #endif
328 
329 extern struct wb_domain global_wb_domain;
330 
331 /* These are exported to sysctl. */
332 extern int dirty_background_ratio;
333 extern unsigned long dirty_background_bytes;
334 extern int vm_dirty_ratio;
335 extern unsigned long vm_dirty_bytes;
336 extern unsigned int dirty_writeback_interval;
337 extern unsigned int dirty_expire_interval;
338 extern unsigned int dirtytime_expire_interval;
339 extern int vm_highmem_is_dirtyable;
340 extern int block_dump;
341 extern int laptop_mode;
342 
343 extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
344                 void __user *buffer, size_t *lenp,
345                 loff_t *ppos);
346 extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
347                 void __user *buffer, size_t *lenp,
348                 loff_t *ppos);
349 extern int dirty_ratio_handler(struct ctl_table *table, int write,
350                 void __user *buffer, size_t *lenp,
351                 loff_t *ppos);
352 extern int dirty_bytes_handler(struct ctl_table *table, int write,
353                 void __user *buffer, size_t *lenp,
354                 loff_t *ppos);
355 int dirtytime_interval_handler(struct ctl_table *table, int write,
356                                void __user *buffer, size_t *lenp, loff_t *ppos);
357 
358 struct ctl_table;
359 int dirty_writeback_centisecs_handler(struct ctl_table *, int,
360                                       void __user *, size_t *, loff_t *);
361 
362 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
363 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
364 
365 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
366 void page_writeback_init(void);
367 void balance_dirty_pages_ratelimited(struct address_space *mapping);
368 bool wb_over_bg_thresh(struct bdi_writeback *wb);
369 
370 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
371                                 void *data);
372 
373 int generic_writepages(struct address_space *mapping,
374                        struct writeback_control *wbc);
375 void tag_pages_for_writeback(struct address_space *mapping,
376                              pgoff_t start, pgoff_t end);
377 int write_cache_pages(struct address_space *mapping,
378                       struct writeback_control *wbc, writepage_t writepage,
379                       void *data);
380 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
381 void writeback_set_ratelimit(void);
382 void tag_pages_for_writeback(struct address_space *mapping,
383                              pgoff_t start, pgoff_t end);
384 
385 void account_page_redirty(struct page *page);
386 
387 #endif          /* WRITEBACK_H */
388 

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