include/linux/writeback.h

   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
  12 DECLARE_PER_CPU(int, dirty_throttle_leaks);
  13
  14 /*
  15  * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
  16  *
  17  *      (thresh - thresh/DIRTY_FULL_SCOPE, thresh)
  18  *
  19  * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
  20  * time) for the dirty pages to drop, unless written enough pages.
  21  *
  22  * The global dirty threshold is normally equal to the global dirty limit,
  23  * except when the system suddenly allocates a lot of anonymous memory and
  24  * knocks down the global dirty threshold quickly, in which case the global
  25  * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
  26  */
  27 #define DIRTY_SCOPE             8
  28 #define DIRTY_FULL_SCOPE        (DIRTY_SCOPE / 2)
  29
  30 struct backing_dev_info;
  31
  32 /*
  33  * fs/fs-writeback.c
  34  */
  35 enum writeback_sync_modes {
  36         WB_SYNC_NONE,   /* Don't wait on anything */
  37         WB_SYNC_ALL,    /* Wait on every mapping */
  38 };
  39
  40 /*
  41  * why some writeback work was initiated
  42  */
  43 enum wb_reason {
  44         WB_REASON_BACKGROUND,
  45         WB_REASON_TRY_TO_FREE_PAGES,
  46         WB_REASON_SYNC,
  47         WB_REASON_PERIODIC,
  48         WB_REASON_LAPTOP_TIMER,
  49         WB_REASON_FREE_MORE_MEM,
  50         WB_REASON_FS_FREE_SPACE,
  51         /*
  52          * There is no bdi forker thread any more and works are done
  53          * by emergency worker, however, this is TPs userland visible
  54          * and we'll be exposing exactly the same information,
  55          * so it has a mismatch name.
  56          */
  57         WB_REASON_FORKER_THREAD,
  58
  59         WB_REASON_MAX,
  60 };
  61
  62 /*
  63  * A control structure which tells the writeback code what to do.  These are
  64  * always on the stack, and hence need no locking.  They are always initialised
  65  * in a manner such that unspecified fields are set to zero.
  66  */
  67 struct writeback_control {
  68         long nr_to_write;               /* Write this many pages, and decrement
  69                                            this for each page written */
  70         long pages_skipped;             /* Pages which were not written */
  71
  72         /*
  73          * For a_ops->writepages(): if start or end are non-zero then this is
  74          * a hint that the filesystem need only write out the pages inside that
  75          * byterange.  The byte at `end' is included in the writeout request.
  76          */
  77         loff_t range_start;
  78         loff_t range_end;
  79
  80         enum writeback_sync_modes sync_mode;
  81
  82         unsigned for_kupdate:1;         /* A kupdate writeback */
  83         unsigned for_background:1;      /* A background writeback */
  84         unsigned tagged_writepages:1;   /* tag-and-write to avoid livelock */
  85         unsigned for_reclaim:1;         /* Invoked from the page allocator */
  86         unsigned range_cyclic:1;        /* range_start is cyclic */
  87         unsigned for_sync:1;            /* sync(2) WB_SYNC_ALL writeback */
  88 };
  89
  90 /*
  91  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
  92  * and are measured against each other in.  There always is one global
  93  * domain, global_wb_domain, that every wb in the system is a member of.
  94  * This allows measuring the relative bandwidth of each wb to distribute
  95  * dirtyable memory accordingly.
  96  */
  97 struct wb_domain {
  98         spinlock_t lock;
  99
 100         /*
 101          * Scale the writeback cache size proportional to the relative
 102          * writeout speed.
 103          *
 104          * We do this by keeping a floating proportion between BDIs, based
 105          * on page writeback completions [end_page_writeback()]. Those
 106          * devices that write out pages fastest will get the larger share,
 107          * while the slower will get a smaller share.
 108          *
 109          * We use page writeout completions because we are interested in
 110          * getting rid of dirty pages. Having them written out is the
 111          * primary goal.
 112          *
 113          * We introduce a concept of time, a period over which we measure
 114          * these events, because demand can/will vary over time. The length
 115          * of this period itself is measured in page writeback completions.
 116          */
 117         struct fprop_global completions;
 118         struct timer_list period_timer; /* timer for aging of completions */
 119         unsigned long period_time;
 120
 121         /*
 122          * The dirtyable memory and dirty threshold could be suddenly
 123          * knocked down by a large amount (eg. on the startup of KVM in a
 124          * swapless system). This may throw the system into deep dirty
 125          * exceeded state and throttle heavy/light dirtiers alike. To
 126          * retain good responsiveness, maintain global_dirty_limit for
 127          * tracking slowly down to the knocked down dirty threshold.
 128          *
 129          * Both fields are protected by ->lock.
 130          */
 131         unsigned long dirty_limit_tstamp;
 132         unsigned long dirty_limit;
 133 };
 134
 135 /**
 136  * wb_domain_size_changed - memory available to a wb_domain has changed
 137  * @dom: wb_domain of interest
 138  *
 139  * This function should be called when the amount of memory available to
 140  * @dom has changed.  It resets @dom's dirty limit parameters to prevent
 141  * the past values which don't match the current configuration from skewing
 142  * dirty throttling.  Without this, when memory size of a wb_domain is
 143  * greatly reduced, the dirty throttling logic may allow too many pages to
 144  * be dirtied leading to consecutive unnecessary OOMs and may get stuck in
 145  * that situation.
 146  */
 147 static inline void wb_domain_size_changed(struct wb_domain *dom)
 148 {
 149         spin_lock(&dom->lock);
 150         dom->dirty_limit_tstamp = jiffies;
 151         dom->dirty_limit = 0;
 152         spin_unlock(&dom->lock);
 153 }
 154
 155 /*
 156  * fs/fs-writeback.c
 157  */
 158 struct bdi_writeback;
 159 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 160 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 161                                                         enum wb_reason reason);
 162 bool try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 163 bool try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 164                                    enum wb_reason reason);
 165 void sync_inodes_sb(struct super_block *);
 166 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
 167 void inode_wait_for_writeback(struct inode *inode);
 168
 169 /* writeback.h requires fs.h; it, too, is not included from here. */
 170 static inline void wait_on_inode(struct inode *inode)
 171 {
 172         might_sleep();
 173         wait_on_bit(&inode->i_state, __I_NEW, TASK_UNINTERRUPTIBLE);
 174 }
 175
 176 /*
 177  * mm/page-writeback.c
 178  */
 179 #ifdef CONFIG_BLOCK
 180 void laptop_io_completion(struct backing_dev_info *info);
 181 void laptop_sync_completion(void);
 182 void laptop_mode_sync(struct work_struct *work);
 183 void laptop_mode_timer_fn(unsigned long data);
 184 #else
 185 static inline void laptop_sync_completion(void) { }
 186 #endif
 187 void throttle_vm_writeout(gfp_t gfp_mask);
 188 bool zone_dirty_ok(struct zone *zone);
 189 int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
 190 #ifdef CONFIG_CGROUP_WRITEBACK
 191 void wb_domain_exit(struct wb_domain *dom);
 192 #endif
 193
 194 extern struct wb_domain global_wb_domain;
 195
 196 /* These are exported to sysctl. */
 197 extern int dirty_background_ratio;
 198 extern unsigned long dirty_background_bytes;
 199 extern int vm_dirty_ratio;
 200 extern unsigned long vm_dirty_bytes;
 201 extern unsigned int dirty_writeback_interval;
 202 extern unsigned int dirty_expire_interval;
 203 extern unsigned int dirtytime_expire_interval;
 204 extern int vm_highmem_is_dirtyable;
 205 extern int block_dump;
 206 extern int laptop_mode;
 207
 208 extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
 209                 void __user *buffer, size_t *lenp,
 210                 loff_t *ppos);
 211 extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
 212                 void __user *buffer, size_t *lenp,
 213                 loff_t *ppos);
 214 extern int dirty_ratio_handler(struct ctl_table *table, int write,
 215                 void __user *buffer, size_t *lenp,
 216                 loff_t *ppos);
 217 extern int dirty_bytes_handler(struct ctl_table *table, int write,
 218                 void __user *buffer, size_t *lenp,
 219                 loff_t *ppos);
 220 int dirtytime_interval_handler(struct ctl_table *table, int write,
 221                                void __user *buffer, size_t *lenp, loff_t *ppos);
 222
 223 struct ctl_table;
 224 int dirty_writeback_centisecs_handler(struct ctl_table *, int,
 225                                       void __user *, size_t *, loff_t *);
 226
 227 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
 228 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
 229
 230 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
 231 void page_writeback_init(void);
 232 void balance_dirty_pages_ratelimited(struct address_space *mapping);
 233 bool wb_over_bg_thresh(struct bdi_writeback *wb);
 234
 235 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
 236                                 void *data);
 237
 238 int generic_writepages(struct address_space *mapping,
 239                        struct writeback_control *wbc);
 240 void tag_pages_for_writeback(struct address_space *mapping,
 241                              pgoff_t start, pgoff_t end);
 242 int write_cache_pages(struct address_space *mapping,
 243                       struct writeback_control *wbc, writepage_t writepage,
 244                       void *data);
 245 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
 246 void writeback_set_ratelimit(void);
 247 void tag_pages_for_writeback(struct address_space *mapping,
 248                              pgoff_t start, pgoff_t end);
 249
 250 void account_page_redirty(struct page *page);
 251
 252 #endif          /* WRITEBACK_H */