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Diffstat (limited to 'mm/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 1414 |
1 files changed, 1414 insertions, 0 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c new file mode 100644 index 00000000..955fe35d --- /dev/null +++ b/mm/page-writeback.c @@ -0,0 +1,1414 @@ +/* + * mm/page-writeback.c + * + * Copyright (C) 2002, Linus Torvalds. + * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> + * + * Contains functions related to writing back dirty pages at the + * address_space level. + * + * 10Apr2002 Andrew Morton + * Initial version + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/spinlock.h> +#include <linux/fs.h> +#include <linux/mm.h> +#include <linux/swap.h> +#include <linux/slab.h> +#include <linux/pagemap.h> +#include <linux/writeback.h> +#include <linux/init.h> +#include <linux/backing-dev.h> +#include <linux/task_io_accounting_ops.h> +#include <linux/blkdev.h> +#include <linux/mpage.h> +#include <linux/rmap.h> +#include <linux/percpu.h> +#include <linux/notifier.h> +#include <linux/smp.h> +#include <linux/sysctl.h> +#include <linux/cpu.h> +#include <linux/syscalls.h> +#include <linux/buffer_head.h> +#include <linux/pagevec.h> +#include <trace/events/writeback.h> + +/* + * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited + * will look to see if it needs to force writeback or throttling. + */ +static long ratelimit_pages = 32; + +/* + * When balance_dirty_pages decides that the caller needs to perform some + * non-background writeback, this is how many pages it will attempt to write. + * It should be somewhat larger than dirtied pages to ensure that reasonably + * large amounts of I/O are submitted. + */ +static inline long sync_writeback_pages(unsigned long dirtied) +{ + if (dirtied < ratelimit_pages) + dirtied = ratelimit_pages; + + return dirtied + dirtied / 2; +} + +/* The following parameters are exported via /proc/sys/vm */ + +/* + * Start background writeback (via writeback threads) at this percentage + */ +int dirty_background_ratio = 10; + +/* + * dirty_background_bytes starts at 0 (disabled) so that it is a function of + * dirty_background_ratio * the amount of dirtyable memory + */ +unsigned long dirty_background_bytes; + +/* + * free highmem will not be subtracted from the total free memory + * for calculating free ratios if vm_highmem_is_dirtyable is true + */ +int vm_highmem_is_dirtyable; + +/* + * The generator of dirty data starts writeback at this percentage + */ +int vm_dirty_ratio = 20; + +/* + * vm_dirty_bytes starts at 0 (disabled) so that it is a function of + * vm_dirty_ratio * the amount of dirtyable memory + */ +unsigned long vm_dirty_bytes; + +/* + * The interval between `kupdate'-style writebacks + */ +unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ + +/* + * The longest time for which data is allowed to remain dirty + */ +unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ + +/* + * Flag that makes the machine dump writes/reads and block dirtyings. + */ +int block_dump; + +/* + * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: + * a full sync is triggered after this time elapses without any disk activity. + */ +int laptop_mode; + +EXPORT_SYMBOL(laptop_mode); + +/* End of sysctl-exported parameters */ + + +/* + * Scale the writeback cache size proportional to the relative writeout speeds. + * + * 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. + * + */ +static struct prop_descriptor vm_completions; +static struct prop_descriptor vm_dirties; + +/* + * couple the period to the dirty_ratio: + * + * period/2 ~ roundup_pow_of_two(dirty limit) + */ +static int calc_period_shift(void) +{ + unsigned long dirty_total; + + if (vm_dirty_bytes) + dirty_total = vm_dirty_bytes / PAGE_SIZE; + else + dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / + 100; + return 2 + ilog2(dirty_total - 1); +} + +/* + * update the period when the dirty threshold changes. + */ +static void update_completion_period(void) +{ + int shift = calc_period_shift(); + prop_change_shift(&vm_completions, shift); + prop_change_shift(&vm_dirties, shift); +} + +int dirty_background_ratio_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + int ret; + + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + if (ret == 0 && write) + dirty_background_bytes = 0; + return ret; +} + +int dirty_background_bytes_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + int ret; + + ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); + if (ret == 0 && write) + dirty_background_ratio = 0; + return ret; +} + +int dirty_ratio_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + int old_ratio = vm_dirty_ratio; + int ret; + + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + if (ret == 0 && write && vm_dirty_ratio != old_ratio) { + update_completion_period(); + vm_dirty_bytes = 0; + } + return ret; +} + + +int dirty_bytes_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + unsigned long old_bytes = vm_dirty_bytes; + int ret; + + ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); + if (ret == 0 && write && vm_dirty_bytes != old_bytes) { + update_completion_period(); + vm_dirty_ratio = 0; + } + return ret; +} + +/* + * Increment the BDI's writeout completion count and the global writeout + * completion count. Called from test_clear_page_writeback(). + */ +static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) +{ + __prop_inc_percpu_max(&vm_completions, &bdi->completions, + bdi->max_prop_frac); +} + +void bdi_writeout_inc(struct backing_dev_info *bdi) +{ + unsigned long flags; + + local_irq_save(flags); + __bdi_writeout_inc(bdi); + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(bdi_writeout_inc); + +void task_dirty_inc(struct task_struct *tsk) +{ + prop_inc_single(&vm_dirties, &tsk->dirties); +} + +/* + * Obtain an accurate fraction of the BDI's portion. + */ +static void bdi_writeout_fraction(struct backing_dev_info *bdi, + long *numerator, long *denominator) +{ + if (bdi_cap_writeback_dirty(bdi)) { + prop_fraction_percpu(&vm_completions, &bdi->completions, + numerator, denominator); + } else { + *numerator = 0; + *denominator = 1; + } +} + +static inline void task_dirties_fraction(struct task_struct *tsk, + long *numerator, long *denominator) +{ + prop_fraction_single(&vm_dirties, &tsk->dirties, + numerator, denominator); +} + +/* + * task_dirty_limit - scale down dirty throttling threshold for one task + * + * task specific dirty limit: + * + * dirty -= (dirty/8) * p_{t} + * + * To protect light/slow dirtying tasks from heavier/fast ones, we start + * throttling individual tasks before reaching the bdi dirty limit. + * Relatively low thresholds will be allocated to heavy dirtiers. So when + * dirty pages grow large, heavy dirtiers will be throttled first, which will + * effectively curb the growth of dirty pages. Light dirtiers with high enough + * dirty threshold may never get throttled. + */ +static unsigned long task_dirty_limit(struct task_struct *tsk, + unsigned long bdi_dirty) +{ + long numerator, denominator; + unsigned long dirty = bdi_dirty; + u64 inv = dirty >> 3; + + task_dirties_fraction(tsk, &numerator, &denominator); + inv *= numerator; + do_div(inv, denominator); + + dirty -= inv; + + return max(dirty, bdi_dirty/2); +} + +/* + * + */ +static unsigned int bdi_min_ratio; + +int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) +{ + int ret = 0; + + spin_lock_bh(&bdi_lock); + if (min_ratio > bdi->max_ratio) { + ret = -EINVAL; + } else { + min_ratio -= bdi->min_ratio; + if (bdi_min_ratio + min_ratio < 100) { + bdi_min_ratio += min_ratio; + bdi->min_ratio += min_ratio; + } else { + ret = -EINVAL; + } + } + spin_unlock_bh(&bdi_lock); + + return ret; +} + +int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) +{ + int ret = 0; + + if (max_ratio > 100) + return -EINVAL; + + spin_lock_bh(&bdi_lock); + if (bdi->min_ratio > max_ratio) { + ret = -EINVAL; + } else { + bdi->max_ratio = max_ratio; + bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; + } + spin_unlock_bh(&bdi_lock); + + return ret; +} +EXPORT_SYMBOL(bdi_set_max_ratio); + +/* + * Work out the current dirty-memory clamping and background writeout + * thresholds. + * + * The main aim here is to lower them aggressively if there is a lot of mapped + * memory around. To avoid stressing page reclaim with lots of unreclaimable + * pages. It is better to clamp down on writers than to start swapping, and + * performing lots of scanning. + * + * We only allow 1/2 of the currently-unmapped memory to be dirtied. + * + * We don't permit the clamping level to fall below 5% - that is getting rather + * excessive. + * + * We make sure that the background writeout level is below the adjusted + * clamping level. + */ + +static unsigned long highmem_dirtyable_memory(unsigned long total) +{ +#ifdef CONFIG_HIGHMEM + int node; + unsigned long x = 0; + + for_each_node_state(node, N_HIGH_MEMORY) { + struct zone *z = + &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; + + x += zone_page_state(z, NR_FREE_PAGES) + + zone_reclaimable_pages(z); + } + /* + * Make sure that the number of highmem pages is never larger + * than the number of the total dirtyable memory. This can only + * occur in very strange VM situations but we want to make sure + * that this does not occur. + */ + return min(x, total); +#else + return 0; +#endif +} + +/** + * determine_dirtyable_memory - amount of memory that may be used + * + * Returns the numebr of pages that can currently be freed and used + * by the kernel for direct mappings. + */ +unsigned long determine_dirtyable_memory(void) +{ + unsigned long x; + + x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); + + if (!vm_highmem_is_dirtyable) + x -= highmem_dirtyable_memory(x); + + return x + 1; /* Ensure that we never return 0 */ +} + +/* + * global_dirty_limits - background-writeback and dirty-throttling thresholds + * + * Calculate the dirty thresholds based on sysctl parameters + * - vm.dirty_background_ratio or vm.dirty_background_bytes + * - vm.dirty_ratio or vm.dirty_bytes + * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and + * real-time tasks. + */ +void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) +{ + unsigned long background; + unsigned long dirty; + unsigned long uninitialized_var(available_memory); + struct task_struct *tsk; + + if (!vm_dirty_bytes || !dirty_background_bytes) + available_memory = determine_dirtyable_memory(); + + if (vm_dirty_bytes) + dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); + else + dirty = (vm_dirty_ratio * available_memory) / 100; + + if (dirty_background_bytes) + background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); + else + background = (dirty_background_ratio * available_memory) / 100; + + if (background >= dirty) + background = dirty / 2; + tsk = current; + if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { + background += background / 4; + dirty += dirty / 4; + } + *pbackground = background; + *pdirty = dirty; +} + +/* + * bdi_dirty_limit - @bdi's share of dirty throttling threshold + * + * Allocate high/low dirty limits to fast/slow devices, in order to prevent + * - starving fast devices + * - piling up dirty pages (that will take long time to sync) on slow devices + * + * The bdi's share of dirty limit will be adapting to its throughput and + * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. + */ +unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) +{ + u64 bdi_dirty; + long numerator, denominator; + + /* + * Calculate this BDI's share of the dirty ratio. + */ + bdi_writeout_fraction(bdi, &numerator, &denominator); + + bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; + bdi_dirty *= numerator; + do_div(bdi_dirty, denominator); + + bdi_dirty += (dirty * bdi->min_ratio) / 100; + if (bdi_dirty > (dirty * bdi->max_ratio) / 100) + bdi_dirty = dirty * bdi->max_ratio / 100; + + return bdi_dirty; +} + +/* + * balance_dirty_pages() must be called by processes which are generating dirty + * data. It looks at the number of dirty pages in the machine and will force + * the caller to perform writeback if the system is over `vm_dirty_ratio'. + * If we're over `background_thresh' then the writeback threads are woken to + * perform some writeout. + */ +static void balance_dirty_pages(struct address_space *mapping, + unsigned long write_chunk) +{ + long nr_reclaimable, bdi_nr_reclaimable; + long nr_writeback, bdi_nr_writeback; + unsigned long background_thresh; + unsigned long dirty_thresh; + unsigned long bdi_thresh; + unsigned long pages_written = 0; + unsigned long pause = 1; + bool dirty_exceeded = false; + struct backing_dev_info *bdi = mapping->backing_dev_info; + + for (;;) { + struct writeback_control wbc = { + .sync_mode = WB_SYNC_NONE, + .older_than_this = NULL, + .nr_to_write = write_chunk, + .range_cyclic = 1, + }; + + nr_reclaimable = global_page_state(NR_FILE_DIRTY) + + global_page_state(NR_UNSTABLE_NFS); + nr_writeback = global_page_state(NR_WRITEBACK); + + global_dirty_limits(&background_thresh, &dirty_thresh); + + /* + * Throttle it only when the background writeback cannot + * catch-up. This avoids (excessively) small writeouts + * when the bdi limits are ramping up. + */ + if (nr_reclaimable + nr_writeback <= + (background_thresh + dirty_thresh) / 2) + break; + + bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); + bdi_thresh = task_dirty_limit(current, bdi_thresh); + + /* + * In order to avoid the stacked BDI deadlock we need + * to ensure we accurately count the 'dirty' pages when + * the threshold is low. + * + * Otherwise it would be possible to get thresh+n pages + * reported dirty, even though there are thresh-m pages + * actually dirty; with m+n sitting in the percpu + * deltas. + */ + if (bdi_thresh < 2*bdi_stat_error(bdi)) { + bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); + bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); + } else { + bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); + bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); + } + + /* + * The bdi thresh is somehow "soft" limit derived from the + * global "hard" limit. The former helps to prevent heavy IO + * bdi or process from holding back light ones; The latter is + * the last resort safeguard. + */ + dirty_exceeded = + (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh) + || (nr_reclaimable + nr_writeback > dirty_thresh); + + if (!dirty_exceeded) + break; + + if (!bdi->dirty_exceeded) + bdi->dirty_exceeded = 1; + + /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. + * Unstable writes are a feature of certain networked + * filesystems (i.e. NFS) in which data may have been + * written to the server's write cache, but has not yet + * been flushed to permanent storage. + * Only move pages to writeback if this bdi is over its + * threshold otherwise wait until the disk writes catch + * up. + */ + trace_wbc_balance_dirty_start(&wbc, bdi); + if (bdi_nr_reclaimable > bdi_thresh) { + writeback_inodes_wb(&bdi->wb, &wbc); + pages_written += write_chunk - wbc.nr_to_write; + trace_wbc_balance_dirty_written(&wbc, bdi); + if (pages_written >= write_chunk) + break; /* We've done our duty */ + } + trace_wbc_balance_dirty_wait(&wbc, bdi); + __set_current_state(TASK_UNINTERRUPTIBLE); + io_schedule_timeout(pause); + + /* + * Increase the delay for each loop, up to our previous + * default of taking a 100ms nap. + */ + pause <<= 1; + if (pause > HZ / 10) + pause = HZ / 10; + } + + if (!dirty_exceeded && bdi->dirty_exceeded) + bdi->dirty_exceeded = 0; + + if (writeback_in_progress(bdi)) + return; + + /* + * In laptop mode, we wait until hitting the higher threshold before + * starting background writeout, and then write out all the way down + * to the lower threshold. So slow writers cause minimal disk activity. + * + * In normal mode, we start background writeout at the lower + * background_thresh, to keep the amount of dirty memory low. + */ + if ((laptop_mode && pages_written) || + (!laptop_mode && (nr_reclaimable > background_thresh))) + bdi_start_background_writeback(bdi); +} + +void set_page_dirty_balance(struct page *page, int page_mkwrite) +{ + if (set_page_dirty(page) || page_mkwrite) { + struct address_space *mapping = page_mapping(page); + + if (mapping) + balance_dirty_pages_ratelimited(mapping); + } +} + +static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0; + +/** + * balance_dirty_pages_ratelimited_nr - balance dirty memory state + * @mapping: address_space which was dirtied + * @nr_pages_dirtied: number of pages which the caller has just dirtied + * + * Processes which are dirtying memory should call in here once for each page + * which was newly dirtied. The function will periodically check the system's + * dirty state and will initiate writeback if needed. + * + * On really big machines, get_writeback_state is expensive, so try to avoid + * calling it too often (ratelimiting). But once we're over the dirty memory + * limit we decrease the ratelimiting by a lot, to prevent individual processes + * from overshooting the limit by (ratelimit_pages) each. + */ +void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, + unsigned long nr_pages_dirtied) +{ + unsigned long ratelimit; + unsigned long *p; + + ratelimit = ratelimit_pages; + if (mapping->backing_dev_info->dirty_exceeded) + ratelimit = 8; + + /* + * Check the rate limiting. Also, we do not want to throttle real-time + * tasks in balance_dirty_pages(). Period. + */ + preempt_disable(); + p = &__get_cpu_var(bdp_ratelimits); + *p += nr_pages_dirtied; + if (unlikely(*p >= ratelimit)) { + ratelimit = sync_writeback_pages(*p); + *p = 0; + preempt_enable(); + balance_dirty_pages(mapping, ratelimit); + return; + } + preempt_enable(); +} +EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); + +void throttle_vm_writeout(gfp_t gfp_mask) +{ + unsigned long background_thresh; + unsigned long dirty_thresh; + + for ( ; ; ) { + global_dirty_limits(&background_thresh, &dirty_thresh); + + /* + * Boost the allowable dirty threshold a bit for page + * allocators so they don't get DoS'ed by heavy writers + */ + dirty_thresh += dirty_thresh / 10; /* wheeee... */ + + if (global_page_state(NR_UNSTABLE_NFS) + + global_page_state(NR_WRITEBACK) <= dirty_thresh) + break; + congestion_wait(BLK_RW_ASYNC, HZ/10); + + /* + * The caller might hold locks which can prevent IO completion + * or progress in the filesystem. So we cannot just sit here + * waiting for IO to complete. + */ + if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) + break; + } +} + +/* + * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs + */ +int dirty_writeback_centisecs_handler(ctl_table *table, int write, + void __user *buffer, size_t *length, loff_t *ppos) +{ + proc_dointvec(table, write, buffer, length, ppos); + bdi_arm_supers_timer(); + return 0; +} + +#ifdef CONFIG_BLOCK +void laptop_mode_timer_fn(unsigned long data) +{ + struct request_queue *q = (struct request_queue *)data; + int nr_pages = global_page_state(NR_FILE_DIRTY) + + global_page_state(NR_UNSTABLE_NFS); + + /* + * We want to write everything out, not just down to the dirty + * threshold + */ + if (bdi_has_dirty_io(&q->backing_dev_info)) + bdi_start_writeback(&q->backing_dev_info, nr_pages); +} + +/* + * We've spun up the disk and we're in laptop mode: schedule writeback + * of all dirty data a few seconds from now. If the flush is already scheduled + * then push it back - the user is still using the disk. + */ +void laptop_io_completion(struct backing_dev_info *info) +{ + mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); +} + +/* + * We're in laptop mode and we've just synced. The sync's writes will have + * caused another writeback to be scheduled by laptop_io_completion. + * Nothing needs to be written back anymore, so we unschedule the writeback. + */ +void laptop_sync_completion(void) +{ + struct backing_dev_info *bdi; + + rcu_read_lock(); + + list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) + del_timer(&bdi->laptop_mode_wb_timer); + + rcu_read_unlock(); +} +#endif + +/* + * If ratelimit_pages is too high then we can get into dirty-data overload + * if a large number of processes all perform writes at the same time. + * If it is too low then SMP machines will call the (expensive) + * get_writeback_state too often. + * + * Here we set ratelimit_pages to a level which ensures that when all CPUs are + * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory + * thresholds before writeback cuts in. + * + * But the limit should not be set too high. Because it also controls the + * amount of memory which the balance_dirty_pages() caller has to write back. + * If this is too large then the caller will block on the IO queue all the + * time. So limit it to four megabytes - the balance_dirty_pages() caller + * will write six megabyte chunks, max. + */ + +void writeback_set_ratelimit(void) +{ + ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); + if (ratelimit_pages < 16) + ratelimit_pages = 16; + if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) + ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; +} + +static int __cpuinit +ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) +{ + writeback_set_ratelimit(); + return NOTIFY_DONE; +} + +static struct notifier_block __cpuinitdata ratelimit_nb = { + .notifier_call = ratelimit_handler, + .next = NULL, +}; + +/* + * Called early on to tune the page writeback dirty limits. + * + * We used to scale dirty pages according to how total memory + * related to pages that could be allocated for buffers (by + * comparing nr_free_buffer_pages() to vm_total_pages. + * + * However, that was when we used "dirty_ratio" to scale with + * all memory, and we don't do that any more. "dirty_ratio" + * is now applied to total non-HIGHPAGE memory (by subtracting + * totalhigh_pages from vm_total_pages), and as such we can't + * get into the old insane situation any more where we had + * large amounts of dirty pages compared to a small amount of + * non-HIGHMEM memory. + * + * But we might still want to scale the dirty_ratio by how + * much memory the box has.. + */ +void __init page_writeback_init(void) +{ + int shift; + + writeback_set_ratelimit(); + register_cpu_notifier(&ratelimit_nb); + + shift = calc_period_shift(); + prop_descriptor_init(&vm_completions, shift); + prop_descriptor_init(&vm_dirties, shift); +} + +/** + * tag_pages_for_writeback - tag pages to be written by write_cache_pages + * @mapping: address space structure to write + * @start: starting page index + * @end: ending page index (inclusive) + * + * This function scans the page range from @start to @end (inclusive) and tags + * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is + * that write_cache_pages (or whoever calls this function) will then use + * TOWRITE tag to identify pages eligible for writeback. This mechanism is + * used to avoid livelocking of writeback by a process steadily creating new + * dirty pages in the file (thus it is important for this function to be quick + * so that it can tag pages faster than a dirtying process can create them). + */ +/* + * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. + */ +void tag_pages_for_writeback(struct address_space *mapping, + pgoff_t start, pgoff_t end) +{ +#define WRITEBACK_TAG_BATCH 4096 + unsigned long tagged; + + do { + spin_lock_irq(&mapping->tree_lock); + tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, + &start, end, WRITEBACK_TAG_BATCH, + PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); + spin_unlock_irq(&mapping->tree_lock); + WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); + cond_resched(); + /* We check 'start' to handle wrapping when end == ~0UL */ + } while (tagged >= WRITEBACK_TAG_BATCH && start); +} +EXPORT_SYMBOL(tag_pages_for_writeback); + +/** + * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. + * @mapping: address space structure to write + * @wbc: subtract the number of written pages from *@wbc->nr_to_write + * @writepage: function called for each page + * @data: data passed to writepage function + * + * If a page is already under I/O, write_cache_pages() skips it, even + * if it's dirty. This is desirable behaviour for memory-cleaning writeback, + * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() + * and msync() need to guarantee that all the data which was dirty at the time + * the call was made get new I/O started against them. If wbc->sync_mode is + * WB_SYNC_ALL then we were called for data integrity and we must wait for + * existing IO to complete. + * + * To avoid livelocks (when other process dirties new pages), we first tag + * pages which should be written back with TOWRITE tag and only then start + * writing them. For data-integrity sync we have to be careful so that we do + * not miss some pages (e.g., because some other process has cleared TOWRITE + * tag we set). The rule we follow is that TOWRITE tag can be cleared only + * by the process clearing the DIRTY tag (and submitting the page for IO). + */ +int write_cache_pages(struct address_space *mapping, + struct writeback_control *wbc, writepage_t writepage, + void *data) +{ + int ret = 0; + int done = 0; + struct pagevec pvec; + int nr_pages; + pgoff_t uninitialized_var(writeback_index); + pgoff_t index; + pgoff_t end; /* Inclusive */ + pgoff_t done_index; + int cycled; + int range_whole = 0; + int tag; + + pagevec_init(&pvec, 0); + if (wbc->range_cyclic) { + writeback_index = mapping->writeback_index; /* prev offset */ + index = writeback_index; + if (index == 0) + cycled = 1; + else + cycled = 0; + end = -1; + } else { + index = wbc->range_start >> PAGE_CACHE_SHIFT; + end = wbc->range_end >> PAGE_CACHE_SHIFT; + if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) + range_whole = 1; + cycled = 1; /* ignore range_cyclic tests */ + } + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) + tag = PAGECACHE_TAG_TOWRITE; + else + tag = PAGECACHE_TAG_DIRTY; +retry: + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) + tag_pages_for_writeback(mapping, index, end); + done_index = index; + while (!done && (index <= end)) { + int i; + + nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, + min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); + if (nr_pages == 0) + break; + + for (i = 0; i < nr_pages; i++) { + struct page *page = pvec.pages[i]; + + /* + * At this point, the page may be truncated or + * invalidated (changing page->mapping to NULL), or + * even swizzled back from swapper_space to tmpfs file + * mapping. However, page->index will not change + * because we have a reference on the page. + */ + if (page->index > end) { + /* + * can't be range_cyclic (1st pass) because + * end == -1 in that case. + */ + done = 1; + break; + } + + done_index = page->index; + + lock_page(page); + + /* + * Page truncated or invalidated. We can freely skip it + * then, even for data integrity operations: the page + * has disappeared concurrently, so there could be no + * real expectation of this data interity operation + * even if there is now a new, dirty page at the same + * pagecache address. + */ + if (unlikely(page->mapping != mapping)) { +continue_unlock: + unlock_page(page); + continue; + } + + if (!PageDirty(page)) { + /* someone wrote it for us */ + goto continue_unlock; + } + + if (PageWriteback(page)) { + if (wbc->sync_mode != WB_SYNC_NONE) + wait_on_page_writeback(page); + else + goto continue_unlock; + } + + BUG_ON(PageWriteback(page)); + if (!clear_page_dirty_for_io(page)) + goto continue_unlock; + + trace_wbc_writepage(wbc, mapping->backing_dev_info); + ret = (*writepage)(page, wbc, data); + if (unlikely(ret)) { + if (ret == AOP_WRITEPAGE_ACTIVATE) { + unlock_page(page); + ret = 0; + } else { + /* + * done_index is set past this page, + * so media errors will not choke + * background writeout for the entire + * file. This has consequences for + * range_cyclic semantics (ie. it may + * not be suitable for data integrity + * writeout). + */ + done_index = page->index + 1; + done = 1; + break; + } + } + + /* + * We stop writing back only if we are not doing + * integrity sync. In case of integrity sync we have to + * keep going until we have written all the pages + * we tagged for writeback prior to entering this loop. + */ + if (--wbc->nr_to_write <= 0 && + wbc->sync_mode == WB_SYNC_NONE) { + done = 1; + break; + } + } + pagevec_release(&pvec); + cond_resched(); + } + if (!cycled && !done) { + /* + * range_cyclic: + * We hit the last page and there is more work to be done: wrap + * back to the start of the file + */ + cycled = 1; + index = 0; + end = writeback_index - 1; + goto retry; + } + if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) + mapping->writeback_index = done_index; + + return ret; +} +EXPORT_SYMBOL(write_cache_pages); + +/* + * Function used by generic_writepages to call the real writepage + * function and set the mapping flags on error + */ +static int __writepage(struct page *page, struct writeback_control *wbc, + void *data) +{ + struct address_space *mapping = data; + int ret = mapping->a_ops->writepage(page, wbc); + mapping_set_error(mapping, ret); + return ret; +} + +/** + * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. + * @mapping: address space structure to write + * @wbc: subtract the number of written pages from *@wbc->nr_to_write + * + * This is a library function, which implements the writepages() + * address_space_operation. + */ +int generic_writepages(struct address_space *mapping, + struct writeback_control *wbc) +{ + struct blk_plug plug; + int ret; + + /* deal with chardevs and other special file */ + if (!mapping->a_ops->writepage) + return 0; + + blk_start_plug(&plug); + ret = write_cache_pages(mapping, wbc, __writepage, mapping); + blk_finish_plug(&plug); + return ret; +} + +EXPORT_SYMBOL(generic_writepages); + +int do_writepages(struct address_space *mapping, struct writeback_control *wbc) +{ + int ret; + + if (wbc->nr_to_write <= 0) + return 0; + if (mapping->a_ops->writepages) + ret = mapping->a_ops->writepages(mapping, wbc); + else + ret = generic_writepages(mapping, wbc); + return ret; +} + +/** + * write_one_page - write out a single page and optionally wait on I/O + * @page: the page to write + * @wait: if true, wait on writeout + * + * The page must be locked by the caller and will be unlocked upon return. + * + * write_one_page() returns a negative error code if I/O failed. + */ +int write_one_page(struct page *page, int wait) +{ + struct address_space *mapping = page->mapping; + int ret = 0; + struct writeback_control wbc = { + .sync_mode = WB_SYNC_ALL, + .nr_to_write = 1, + }; + + BUG_ON(!PageLocked(page)); + + if (wait) + wait_on_page_writeback(page); + + if (clear_page_dirty_for_io(page)) { + page_cache_get(page); + ret = mapping->a_ops->writepage(page, &wbc); + if (ret == 0 && wait) { + wait_on_page_writeback(page); + if (PageError(page)) + ret = -EIO; + } + page_cache_release(page); + } else { + unlock_page(page); + } + return ret; +} +EXPORT_SYMBOL(write_one_page); + +/* + * For address_spaces which do not use buffers nor write back. + */ +int __set_page_dirty_no_writeback(struct page *page) +{ + if (!PageDirty(page)) + return !TestSetPageDirty(page); + return 0; +} + +/* + * Helper function for set_page_dirty family. + * NOTE: This relies on being atomic wrt interrupts. + */ +void account_page_dirtied(struct page *page, struct address_space *mapping) +{ + if (mapping_cap_account_dirty(mapping)) { + __inc_zone_page_state(page, NR_FILE_DIRTY); + __inc_zone_page_state(page, NR_DIRTIED); + __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); + task_dirty_inc(current); + task_io_account_write(PAGE_CACHE_SIZE); + } +} +EXPORT_SYMBOL(account_page_dirtied); + +/* + * Helper function for set_page_writeback family. + * NOTE: Unlike account_page_dirtied this does not rely on being atomic + * wrt interrupts. + */ +void account_page_writeback(struct page *page) +{ + inc_zone_page_state(page, NR_WRITEBACK); + inc_zone_page_state(page, NR_WRITTEN); +} +EXPORT_SYMBOL(account_page_writeback); + +/* + * For address_spaces which do not use buffers. Just tag the page as dirty in + * its radix tree. + * + * This is also used when a single buffer is being dirtied: we want to set the + * page dirty in that case, but not all the buffers. This is a "bottom-up" + * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. + * + * Most callers have locked the page, which pins the address_space in memory. + * But zap_pte_range() does not lock the page, however in that case the + * mapping is pinned by the vma's ->vm_file reference. + * + * We take care to handle the case where the page was truncated from the + * mapping by re-checking page_mapping() inside tree_lock. + */ +int __set_page_dirty_nobuffers(struct page *page) +{ + if (!TestSetPageDirty(page)) { + struct address_space *mapping = page_mapping(page); + struct address_space *mapping2; + + if (!mapping) + return 1; + + spin_lock_irq(&mapping->tree_lock); + mapping2 = page_mapping(page); + if (mapping2) { /* Race with truncate? */ + BUG_ON(mapping2 != mapping); + WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); + account_page_dirtied(page, mapping); + radix_tree_tag_set(&mapping->page_tree, + page_index(page), PAGECACHE_TAG_DIRTY); + } + spin_unlock_irq(&mapping->tree_lock); + if (mapping->host) { + /* !PageAnon && !swapper_space */ + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); + } + return 1; + } + return 0; +} +EXPORT_SYMBOL(__set_page_dirty_nobuffers); + +/* + * When a writepage implementation decides that it doesn't want to write this + * page for some reason, it should redirty the locked page via + * redirty_page_for_writepage() and it should then unlock the page and return 0 + */ +int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) +{ + wbc->pages_skipped++; + return __set_page_dirty_nobuffers(page); +} +EXPORT_SYMBOL(redirty_page_for_writepage); + +/* + * Dirty a page. + * + * For pages with a mapping this should be done under the page lock + * for the benefit of asynchronous memory errors who prefer a consistent + * dirty state. This rule can be broken in some special cases, + * but should be better not to. + * + * If the mapping doesn't provide a set_page_dirty a_op, then + * just fall through and assume that it wants buffer_heads. + */ +int set_page_dirty(struct page *page) +{ + struct address_space *mapping = page_mapping(page); + + if (likely(mapping)) { + int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; + /* + * readahead/lru_deactivate_page could remain + * PG_readahead/PG_reclaim due to race with end_page_writeback + * About readahead, if the page is written, the flags would be + * reset. So no problem. + * About lru_deactivate_page, if the page is redirty, the flag + * will be reset. So no problem. but if the page is used by readahead + * it will confuse readahead and make it restart the size rampup + * process. But it's a trivial problem. + */ + ClearPageReclaim(page); +#ifdef CONFIG_BLOCK + if (!spd) + spd = __set_page_dirty_buffers; +#endif + return (*spd)(page); + } + if (!PageDirty(page)) { + if (!TestSetPageDirty(page)) + return 1; + } + return 0; +} +EXPORT_SYMBOL(set_page_dirty); + +/* + * set_page_dirty() is racy if the caller has no reference against + * page->mapping->host, and if the page is unlocked. This is because another + * CPU could truncate the page off the mapping and then free the mapping. + * + * Usually, the page _is_ locked, or the caller is a user-space process which + * holds a reference on the inode by having an open file. + * + * In other cases, the page should be locked before running set_page_dirty(). + */ +int set_page_dirty_lock(struct page *page) +{ + int ret; + + lock_page(page); + ret = set_page_dirty(page); + unlock_page(page); + return ret; +} +EXPORT_SYMBOL(set_page_dirty_lock); + +/* + * Clear a page's dirty flag, while caring for dirty memory accounting. + * Returns true if the page was previously dirty. + * + * This is for preparing to put the page under writeout. We leave the page + * tagged as dirty in the radix tree so that a concurrent write-for-sync + * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage + * implementation will run either set_page_writeback() or set_page_dirty(), + * at which stage we bring the page's dirty flag and radix-tree dirty tag + * back into sync. + * + * This incoherency between the page's dirty flag and radix-tree tag is + * unfortunate, but it only exists while the page is locked. + */ +int clear_page_dirty_for_io(struct page *page) +{ + struct address_space *mapping = page_mapping(page); + + BUG_ON(!PageLocked(page)); + + if (mapping && mapping_cap_account_dirty(mapping)) { + /* + * Yes, Virginia, this is indeed insane. + * + * We use this sequence to make sure that + * (a) we account for dirty stats properly + * (b) we tell the low-level filesystem to + * mark the whole page dirty if it was + * dirty in a pagetable. Only to then + * (c) clean the page again and return 1 to + * cause the writeback. + * + * This way we avoid all nasty races with the + * dirty bit in multiple places and clearing + * them concurrently from different threads. + * + * Note! Normally the "set_page_dirty(page)" + * has no effect on the actual dirty bit - since + * that will already usually be set. But we + * need the side effects, and it can help us + * avoid races. + * + * We basically use the page "master dirty bit" + * as a serialization point for all the different + * threads doing their things. + */ + if (page_mkclean(page)) + set_page_dirty(page); + /* + * We carefully synchronise fault handlers against + * installing a dirty pte and marking the page dirty + * at this point. We do this by having them hold the + * page lock at some point after installing their + * pte, but before marking the page dirty. + * Pages are always locked coming in here, so we get + * the desired exclusion. See mm/memory.c:do_wp_page() + * for more comments. + */ + if (TestClearPageDirty(page)) { + dec_zone_page_state(page, NR_FILE_DIRTY); + dec_bdi_stat(mapping->backing_dev_info, + BDI_RECLAIMABLE); + return 1; + } + return 0; + } + return TestClearPageDirty(page); +} +EXPORT_SYMBOL(clear_page_dirty_for_io); + +int test_clear_page_writeback(struct page *page) +{ + struct address_space *mapping = page_mapping(page); + int ret; + + if (mapping) { + struct backing_dev_info *bdi = mapping->backing_dev_info; + unsigned long flags; + + spin_lock_irqsave(&mapping->tree_lock, flags); + ret = TestClearPageWriteback(page); + if (ret) { + radix_tree_tag_clear(&mapping->page_tree, + page_index(page), + PAGECACHE_TAG_WRITEBACK); + if (bdi_cap_account_writeback(bdi)) { + __dec_bdi_stat(bdi, BDI_WRITEBACK); + __bdi_writeout_inc(bdi); + } + } + spin_unlock_irqrestore(&mapping->tree_lock, flags); + } else { + ret = TestClearPageWriteback(page); + } + if (ret) + dec_zone_page_state(page, NR_WRITEBACK); + return ret; +} + +int test_set_page_writeback(struct page *page) +{ + struct address_space *mapping = page_mapping(page); + int ret; + + if (mapping) { + struct backing_dev_info *bdi = mapping->backing_dev_info; + unsigned long flags; + + spin_lock_irqsave(&mapping->tree_lock, flags); + ret = TestSetPageWriteback(page); + if (!ret) { + radix_tree_tag_set(&mapping->page_tree, + page_index(page), + PAGECACHE_TAG_WRITEBACK); + if (bdi_cap_account_writeback(bdi)) + __inc_bdi_stat(bdi, BDI_WRITEBACK); + } + if (!PageDirty(page)) + radix_tree_tag_clear(&mapping->page_tree, + page_index(page), + PAGECACHE_TAG_DIRTY); + radix_tree_tag_clear(&mapping->page_tree, + page_index(page), + PAGECACHE_TAG_TOWRITE); + spin_unlock_irqrestore(&mapping->tree_lock, flags); + } else { + ret = TestSetPageWriteback(page); + } + if (!ret) + account_page_writeback(page); + return ret; + +} +EXPORT_SYMBOL(test_set_page_writeback); + +/* + * Return true if any of the pages in the mapping are marked with the + * passed tag. + */ +int mapping_tagged(struct address_space *mapping, int tag) +{ + int ret; + rcu_read_lock(); + ret = radix_tree_tagged(&mapping->page_tree, tag); + rcu_read_unlock(); + return ret; +} +EXPORT_SYMBOL(mapping_tagged); |