include/linux/writeback.h

   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 #include <linux/blk-cgroup.h>
  15
  16 struct bio;
  17
  18 DECLARE_PER_CPU(int, dirty_throttle_leaks);
  19
  20 /*
  21  * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
  22  *
  23  *      (thresh - thresh/DIRTY_FULL_SCOPE, thresh)
  24  *
  25  * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
  26  * time) for the dirty pages to drop, unless written enough pages.
  27  *
  28  * The global dirty threshold is normally equal to the global dirty limit,
  29  * except when the system suddenly allocates a lot of anonymous memory and
  30  * knocks down the global dirty threshold quickly, in which case the global
  31  * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
  32  */
  33 #define DIRTY_SCOPE             8
  34 #define DIRTY_FULL_SCOPE        (DIRTY_SCOPE / 2)
  35
  36 struct backing_dev_info;
  37
  38 /*
  39  * fs/fs-writeback.c
  40  */
  41 enum writeback_sync_modes {
  42         WB_SYNC_NONE,   /* Don't wait on anything */
  43         WB_SYNC_ALL,    /* Wait on every mapping */
  44 };
  45
  46 /*
  47  * A control structure which tells the writeback code what to do.  These are
  48  * always on the stack, and hence need no locking.  They are always initialised
  49  * in a manner such that unspecified fields are set to zero.
  50  */
  51 struct writeback_control {
  52         long nr_to_write;               /* Write this many pages, and decrement
  53                                            this for each page written */
  54         long pages_skipped;             /* Pages which were not written */
  55
  56         /*
  57          * For a_ops->writepages(): if start or end are non-zero then this is
  58          * a hint that the filesystem need only write out the pages inside that
  59          * byterange.  The byte at `end' is included in the writeout request.
  60          */
  61         loff_t range_start;
  62         loff_t range_end;
  63
  64         enum writeback_sync_modes sync_mode;
  65
  66         unsigned for_kupdate:1;         /* A kupdate writeback */
  67         unsigned for_background:1;      /* A background writeback */
  68         unsigned tagged_writepages:1;   /* tag-and-write to avoid livelock */
  69         unsigned for_reclaim:1;         /* Invoked from the page allocator */
  70         unsigned range_cyclic:1;        /* range_start is cyclic */
  71         unsigned for_sync:1;            /* sync(2) WB_SYNC_ALL writeback */
  72
  73         /*
  74          * When writeback IOs are bounced through async layers, only the
  75          * initial synchronous phase should be accounted towards inode
  76          * cgroup ownership arbitration to avoid confusion.  Later stages
  77          * can set the following flag to disable the accounting.
  78          */
  79         unsigned no_cgroup_owner:1;
  80
  81         unsigned punt_to_cgroup:1;      /* cgrp punting, see __REQ_CGROUP_PUNT */
  82
  83 #ifdef CONFIG_CGROUP_WRITEBACK
  84         struct bdi_writeback *wb;       /* wb this writeback is issued under */
  85         struct inode *inode;            /* inode being written out */
  86
  87         /* foreign inode detection, see wbc_detach_inode() */
  88         int wb_id;                      /* current wb id */
  89         int wb_lcand_id;                /* last foreign candidate wb id */
  90         int wb_tcand_id;                /* this foreign candidate wb id */
  91         size_t wb_bytes;                /* bytes written by current wb */
  92         size_t wb_lcand_bytes;          /* bytes written by last candidate */
  93         size_t wb_tcand_bytes;          /* bytes written by this candidate */
  94 #endif
  95 };
  96
  97 static inline int wbc_to_write_flags(struct writeback_control *wbc)
  98 {
  99         int flags = 0;
 100
 101         if (wbc->punt_to_cgroup)
 102                 flags = REQ_CGROUP_PUNT;
 103
 104         if (wbc->sync_mode == WB_SYNC_ALL)
 105                 flags |= REQ_SYNC;
 106         else if (wbc->for_kupdate || wbc->for_background)
 107                 flags |= REQ_BACKGROUND;
 108
 109         return flags;
 110 }
 111
 112 static inline struct cgroup_subsys_state *
 113 wbc_blkcg_css(struct writeback_control *wbc)
 114 {
 115 #ifdef CONFIG_CGROUP_WRITEBACK
 116         if (wbc->wb)
 117                 return wbc->wb->blkcg_css;
 118 #endif
 119         return blkcg_root_css;
 120 }
 121
 122 /*
 123  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
 124  * and are measured against each other in.  There always is one global
 125  * domain, global_wb_domain, that every wb in the system is a member of.
 126  * This allows measuring the relative bandwidth of each wb to distribute
 127  * dirtyable memory accordingly.
 128  */
 129 struct wb_domain {
 130         spinlock_t lock;
 131
 132         /*
 133          * Scale the writeback cache size proportional to the relative
 134          * writeout speed.
 135          *
 136          * We do this by keeping a floating proportion between BDIs, based
 137          * on page writeback completions [end_page_writeback()]. Those
 138          * devices that write out pages fastest will get the larger share,
 139          * while the slower will get a smaller share.
 140          *
 141          * We use page writeout completions because we are interested in
 142          * getting rid of dirty pages. Having them written out is the
 143          * primary goal.
 144          *
 145          * We introduce a concept of time, a period over which we measure
 146          * these events, because demand can/will vary over time. The length
 147          * of this period itself is measured in page writeback completions.
 148          */
 149         struct fprop_global completions;
 150         struct timer_list period_timer; /* timer for aging of completions */
 151         unsigned long period_time;
 152
 153         /*
 154          * The dirtyable memory and dirty threshold could be suddenly
 155          * knocked down by a large amount (eg. on the startup of KVM in a
 156          * swapless system). This may throw the system into deep dirty
 157          * exceeded state and throttle heavy/light dirtiers alike. To
 158          * retain good responsiveness, maintain global_dirty_limit for
 159          * tracking slowly down to the knocked down dirty threshold.
 160          *
 161          * Both fields are protected by ->lock.
 162          */
 163         unsigned long dirty_limit_tstamp;
 164         unsigned long dirty_limit;
 165 };
 166
 167 /**
 168  * wb_domain_size_changed - memory available to a wb_domain has changed
 169  * @dom: wb_domain of interest
 170  *
 171  * This function should be called when the amount of memory available to
 172  * @dom has changed.  It resets @dom's dirty limit parameters to prevent
 173  * the past values which don't match the current configuration from skewing
 174  * dirty throttling.  Without this, when memory size of a wb_domain is
 175  * greatly reduced, the dirty throttling logic may allow too many pages to
 176  * be dirtied leading to consecutive unnecessary OOMs and may get stuck in
 177  * that situation.
 178  */
 179 static inline void wb_domain_size_changed(struct wb_domain *dom)
 180 {
 181         spin_lock(&dom->lock);
 182         dom->dirty_limit_tstamp = jiffies;
 183         dom->dirty_limit = 0;
 184         spin_unlock(&dom->lock);
 185 }
 186
 187 /*
 188  * fs/fs-writeback.c
 189  */
 190 struct bdi_writeback;
 191 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 192 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 193                                                         enum wb_reason reason);
 194 void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason);
 195 void sync_inodes_sb(struct super_block *);
 196 void wakeup_flusher_threads(enum wb_reason reason);
 197 void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
 198                                 enum wb_reason reason);
 199 void inode_wait_for_writeback(struct inode *inode);
 200
 201 /* writeback.h requires fs.h; it, too, is not included from here. */
 202 static inline void wait_on_inode(struct inode *inode)
 203 {
 204         might_sleep();
 205         wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
 206 }
 207
 208 #ifdef CONFIG_CGROUP_WRITEBACK
 209
 210 #include <linux/cgroup.h>
 211 #include <linux/bio.h>
 212
 213 void __inode_attach_wb(struct inode *inode, struct page *page);
 214 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
 215                                  struct inode *inode)
 216         __releases(&inode->i_lock);
 217 void wbc_detach_inode(struct writeback_control *wbc);
 218 void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
 219                               size_t bytes);
 220 void cgroup_writeback_umount(void);
 221
 222 /**
 223  * inode_attach_wb - associate an inode with its wb
 224  * @inode: inode of interest
 225  * @page: page being dirtied (may be NULL)
 226  *
 227  * If @inode doesn't have its wb, associate it with the wb matching the
 228  * memcg of @page or, if @page is NULL, %current.  May be called w/ or w/o
 229  * @inode->i_lock.
 230  */
 231 static inline void inode_attach_wb(struct inode *inode, struct page *page)
 232 {
 233         if (!inode->i_wb)
 234                 __inode_attach_wb(inode, page);
 235 }
 236
 237 /**
 238  * inode_detach_wb - disassociate an inode from its wb
 239  * @inode: inode of interest
 240  *
 241  * @inode is being freed.  Detach from its wb.
 242  */
 243 static inline void inode_detach_wb(struct inode *inode)
 244 {
 245         if (inode->i_wb) {
 246                 WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
 247                 wb_put(inode->i_wb);
 248                 inode->i_wb = NULL;
 249         }
 250 }
 251
 252 /**
 253  * wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
 254  * @wbc: writeback_control of interest
 255  * @inode: target inode
 256  *
 257  * This function is to be used by __filemap_fdatawrite_range(), which is an
 258  * alternative entry point into writeback code, and first ensures @inode is
 259  * associated with a bdi_writeback and attaches it to @wbc.
 260  */
 261 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
 262                                                struct inode *inode)
 263 {
 264         spin_lock(&inode->i_lock);
 265         inode_attach_wb(inode, NULL);
 266         wbc_attach_and_unlock_inode(wbc, inode);
 267 }
 268
 269 /**
 270  * wbc_init_bio - writeback specific initializtion of bio
 271  * @wbc: writeback_control for the writeback in progress
 272  * @bio: bio to be initialized
 273  *
 274  * @bio is a part of the writeback in progress controlled by @wbc.  Perform
 275  * writeback specific initialization.  This is used to apply the cgroup
 276  * writeback context.  Must be called after the bio has been associated with
 277  * a device.
 278  */
 279 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
 280 {
 281         /*
 282          * pageout() path doesn't attach @wbc to the inode being written
 283          * out.  This is intentional as we don't want the function to block
 284          * behind a slow cgroup.  Ultimately, we want pageout() to kick off
 285          * regular writeback instead of writing things out itself.
 286          */
 287         if (wbc->wb)
 288                 bio_associate_blkg_from_css(bio, wbc->wb->blkcg_css);
 289 }
 290
 291 #else   /* CONFIG_CGROUP_WRITEBACK */
 292
 293 static inline void inode_attach_wb(struct inode *inode, struct page *page)
 294 {
 295 }
 296
 297 static inline void inode_detach_wb(struct inode *inode)
 298 {
 299 }
 300
 301 static inline void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
 302                                                struct inode *inode)
 303         __releases(&inode->i_lock)
 304 {
 305         spin_unlock(&inode->i_lock);
 306 }
 307
 308 static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
 309                                                struct inode *inode)
 310 {
 311 }
 312
 313 static inline void wbc_detach_inode(struct writeback_control *wbc)
 314 {
 315 }
 316
 317 static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
 318 {
 319 }
 320
 321 static inline void wbc_account_cgroup_owner(struct writeback_control *wbc,
 322                                             struct page *page, size_t bytes)
 323 {
 324 }
 325
 326 static inline void cgroup_writeback_umount(void)
 327 {
 328 }
 329
 330 #endif  /* CONFIG_CGROUP_WRITEBACK */
 331
 332 /*
 333  * mm/page-writeback.c
 334  */
 335 #ifdef CONFIG_BLOCK
 336 void laptop_io_completion(struct backing_dev_info *info);
 337 void laptop_sync_completion(void);
 338 void laptop_mode_sync(struct work_struct *work);
 339 void laptop_mode_timer_fn(struct timer_list *t);
 340 #else
 341 static inline void laptop_sync_completion(void) { }
 342 #endif
 343 bool node_dirty_ok(struct pglist_data *pgdat);
 344 int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
 345 #ifdef CONFIG_CGROUP_WRITEBACK
 346 void wb_domain_exit(struct wb_domain *dom);
 347 #endif
 348
 349 extern struct wb_domain global_wb_domain;
 350
 351 /* These are exported to sysctl. */
 352 extern int dirty_background_ratio;
 353 extern unsigned long dirty_background_bytes;
 354 extern int vm_dirty_ratio;
 355 extern unsigned long vm_dirty_bytes;
 356 extern unsigned int dirty_writeback_interval;
 357 extern unsigned int dirty_expire_interval;
 358 extern unsigned int dirtytime_expire_interval;
 359 extern int vm_highmem_is_dirtyable;
 360 extern int block_dump;
 361 extern int laptop_mode;
 362
 363 extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
 364                 void __user *buffer, size_t *lenp,
 365                 loff_t *ppos);
 366 extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
 367                 void __user *buffer, size_t *lenp,
 368                 loff_t *ppos);
 369 extern int dirty_ratio_handler(struct ctl_table *table, int write,
 370                 void __user *buffer, size_t *lenp,
 371                 loff_t *ppos);
 372 extern int dirty_bytes_handler(struct ctl_table *table, int write,
 373                 void __user *buffer, size_t *lenp,
 374                 loff_t *ppos);
 375 int dirtytime_interval_handler(struct ctl_table *table, int write,
 376                                void __user *buffer, size_t *lenp, loff_t *ppos);
 377
 378 struct ctl_table;
 379 int dirty_writeback_centisecs_handler(struct ctl_table *, int,
 380                                       void __user *, size_t *, loff_t *);
 381
 382 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
 383 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
 384
 385 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
 386 void balance_dirty_pages_ratelimited(struct address_space *mapping);
 387 bool wb_over_bg_thresh(struct bdi_writeback *wb);
 388
 389 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
 390                                 void *data);
 391
 392 int generic_writepages(struct address_space *mapping,
 393                        struct writeback_control *wbc);
 394 void tag_pages_for_writeback(struct address_space *mapping,
 395                              pgoff_t start, pgoff_t end);
 396 int write_cache_pages(struct address_space *mapping,
 397                       struct writeback_control *wbc, writepage_t writepage,
 398                       void *data);
 399 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
 400 void writeback_set_ratelimit(void);
 401 void tag_pages_for_writeback(struct address_space *mapping,
 402                              pgoff_t start, pgoff_t end);
 403
 404 void account_page_redirty(struct page *page);
 405
 406 void sb_mark_inode_writeback(struct inode *inode);
 407 void sb_clear_inode_writeback(struct inode *inode);
 408
 409 #endif          /* WRITEBACK_H */