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Diffstat (limited to 'kernel/mm/page-writeback.c')
| -rw-r--r-- | kernel/mm/page-writeback.c | 2436 |
1 files changed, 2436 insertions, 0 deletions
diff --git a/kernel/mm/page-writeback.c b/kernel/mm/page-writeback.c new file mode 100644 index 000000000..eb59f7eea --- /dev/null +++ b/kernel/mm/page-writeback.c @@ -0,0 +1,2436 @@ +/* + * 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/export.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> /* __set_page_dirty_buffers */ +#include <linux/pagevec.h> +#include <linux/timer.h> +#include <linux/sched/rt.h> +#include <linux/mm_inline.h> +#include <trace/events/writeback.h> + +#include "internal.h" + +/* + * Sleep at most 200ms at a time in balance_dirty_pages(). + */ +#define MAX_PAUSE max(HZ/5, 1) + +/* + * Try to keep balance_dirty_pages() call intervals higher than this many pages + * by raising pause time to max_pause when falls below it. + */ +#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) + +/* + * Estimate write bandwidth at 200ms intervals. + */ +#define BANDWIDTH_INTERVAL max(HZ/5, 1) + +#define RATELIMIT_CALC_SHIFT 10 + +/* + * 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; + +/* 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 */ + +EXPORT_SYMBOL_GPL(dirty_writeback_interval); + +/* + * 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 */ + +unsigned long global_dirty_limit; + +/* + * 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 fprop_global writeout_completions; + +static void writeout_period(unsigned long t); +/* Timer for aging of writeout_completions */ +static struct timer_list writeout_period_timer = + TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0); +static unsigned long writeout_period_time = 0; + +/* + * Length of period for aging writeout fractions of bdis. This is an + * arbitrarily chosen number. The longer the period, the slower fractions will + * reflect changes in current writeout rate. + */ +#define VM_COMPLETIONS_PERIOD_LEN (3*HZ) + +/* + * In a memory zone, there is a certain amount of pages we consider + * available for the page cache, which is essentially the number of + * free and reclaimable pages, minus some zone reserves to protect + * lowmem and the ability to uphold the zone's watermarks without + * requiring writeback. + * + * This number of dirtyable pages is the base value of which the + * user-configurable dirty ratio is the effictive number of pages that + * are allowed to be actually dirtied. Per individual zone, or + * globally by using the sum of dirtyable pages over all zones. + * + * Because the user is allowed to specify the dirty limit globally as + * absolute number of bytes, calculating the per-zone dirty limit can + * require translating the configured limit into a percentage of + * global dirtyable memory first. + */ + +/** + * zone_dirtyable_memory - number of dirtyable pages in a zone + * @zone: the zone + * + * Returns the zone's number of pages potentially available for dirty + * page cache. This is the base value for the per-zone dirty limits. + */ +static unsigned long zone_dirtyable_memory(struct zone *zone) +{ + unsigned long nr_pages; + + nr_pages = zone_page_state(zone, NR_FREE_PAGES); + nr_pages -= min(nr_pages, zone->dirty_balance_reserve); + + nr_pages += zone_page_state(zone, NR_INACTIVE_FILE); + nr_pages += zone_page_state(zone, NR_ACTIVE_FILE); + + return nr_pages; +} + +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_dirtyable_memory(z); + } + /* + * Unreclaimable memory (kernel memory or anonymous memory + * without swap) can bring down the dirtyable pages below + * the zone's dirty balance reserve and the above calculation + * will underflow. However we still want to add in nodes + * which are below threshold (negative values) to get a more + * accurate calculation but make sure that the total never + * underflows. + */ + if ((long)x < 0) + x = 0; + + /* + * 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 +} + +/** + * global_dirtyable_memory - number of globally dirtyable pages + * + * Returns the global number of pages potentially available for dirty + * page cache. This is the base value for the global dirty limits. + */ +static unsigned long global_dirtyable_memory(void) +{ + unsigned long x; + + x = global_page_state(NR_FREE_PAGES); + x -= min(x, dirty_balance_reserve); + + x += global_page_state(NR_INACTIVE_FILE); + x += global_page_state(NR_ACTIVE_FILE); + + 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) +{ + const unsigned long available_memory = global_dirtyable_memory(); + unsigned long background; + unsigned long dirty; + struct task_struct *tsk; + + 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; + trace_global_dirty_state(background, dirty); +} + +/** + * zone_dirty_limit - maximum number of dirty pages allowed in a zone + * @zone: the zone + * + * Returns the maximum number of dirty pages allowed in a zone, based + * on the zone's dirtyable memory. + */ +static unsigned long zone_dirty_limit(struct zone *zone) +{ + unsigned long zone_memory = zone_dirtyable_memory(zone); + struct task_struct *tsk = current; + unsigned long dirty; + + if (vm_dirty_bytes) + dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * + zone_memory / global_dirtyable_memory(); + else + dirty = vm_dirty_ratio * zone_memory / 100; + + if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) + dirty += dirty / 4; + + return dirty; +} + +/** + * zone_dirty_ok - tells whether a zone is within its dirty limits + * @zone: the zone to check + * + * Returns %true when the dirty pages in @zone are within the zone's + * dirty limit, %false if the limit is exceeded. + */ +bool zone_dirty_ok(struct zone *zone) +{ + unsigned long limit = zone_dirty_limit(zone); + + return zone_page_state(zone, NR_FILE_DIRTY) + + zone_page_state(zone, NR_UNSTABLE_NFS) + + zone_page_state(zone, NR_WRITEBACK) <= limit; +} + +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) { + writeback_set_ratelimit(); + 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) { + writeback_set_ratelimit(); + vm_dirty_ratio = 0; + } + return ret; +} + +static unsigned long wp_next_time(unsigned long cur_time) +{ + cur_time += VM_COMPLETIONS_PERIOD_LEN; + /* 0 has a special meaning... */ + if (!cur_time) + return 1; + return cur_time; +} + +/* + * 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) +{ + __inc_bdi_stat(bdi, BDI_WRITTEN); + __fprop_inc_percpu_max(&writeout_completions, &bdi->completions, + bdi->max_prop_frac); + /* First event after period switching was turned off? */ + if (!unlikely(writeout_period_time)) { + /* + * We can race with other __bdi_writeout_inc calls here but + * it does not cause any harm since the resulting time when + * timer will fire and what is in writeout_period_time will be + * roughly the same. + */ + writeout_period_time = wp_next_time(jiffies); + mod_timer(&writeout_period_timer, writeout_period_time); + } +} + +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); + +/* + * Obtain an accurate fraction of the BDI's portion. + */ +static void bdi_writeout_fraction(struct backing_dev_info *bdi, + long *numerator, long *denominator) +{ + fprop_fraction_percpu(&writeout_completions, &bdi->completions, + numerator, denominator); +} + +/* + * On idle system, we can be called long after we scheduled because we use + * deferred timers so count with missed periods. + */ +static void writeout_period(unsigned long t) +{ + int miss_periods = (jiffies - writeout_period_time) / + VM_COMPLETIONS_PERIOD_LEN; + + if (fprop_new_period(&writeout_completions, miss_periods + 1)) { + writeout_period_time = wp_next_time(writeout_period_time + + miss_periods * VM_COMPLETIONS_PERIOD_LEN); + mod_timer(&writeout_period_timer, writeout_period_time); + } else { + /* + * Aging has zeroed all fractions. Stop wasting CPU on period + * updates. + */ + writeout_period_time = 0; + } +} + +/* + * bdi_min_ratio keeps the sum of the minimum dirty shares of all + * registered backing devices, which, for obvious reasons, can not + * exceed 100%. + */ +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 = (FPROP_FRAC_BASE * max_ratio) / 100; + } + spin_unlock_bh(&bdi_lock); + + return ret; +} +EXPORT_SYMBOL(bdi_set_max_ratio); + +static unsigned long dirty_freerun_ceiling(unsigned long thresh, + unsigned long bg_thresh) +{ + return (thresh + bg_thresh) / 2; +} + +static unsigned long hard_dirty_limit(unsigned long thresh) +{ + return max(thresh, global_dirty_limit); +} + +/** + * bdi_dirty_limit - @bdi's share of dirty throttling threshold + * @bdi: the backing_dev_info to query + * @dirty: global dirty limit in pages + * + * Returns @bdi's dirty limit in pages. The term "dirty" in the context of + * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. + * + * Note that balance_dirty_pages() will only seriously take it as a hard limit + * when sleeping max_pause per page is not enough to keep the dirty pages under + * control. For example, when the device is completely stalled due to some error + * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. + * In the other normal situations, it acts more gently by throttling the tasks + * more (rather than completely block them) when the bdi dirty pages go high. + * + * It allocates 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; +} + +/* + * setpoint - dirty 3 + * f(dirty) := 1.0 + (----------------) + * limit - setpoint + * + * it's a 3rd order polynomial that subjects to + * + * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast + * (2) f(setpoint) = 1.0 => the balance point + * (3) f(limit) = 0 => the hard limit + * (4) df/dx <= 0 => negative feedback control + * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) + * => fast response on large errors; small oscillation near setpoint + */ +static long long pos_ratio_polynom(unsigned long setpoint, + unsigned long dirty, + unsigned long limit) +{ + long long pos_ratio; + long x; + + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, + (limit - setpoint) | 1); + pos_ratio = x; + pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; + pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; + pos_ratio += 1 << RATELIMIT_CALC_SHIFT; + + return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT); +} + +/* + * Dirty position control. + * + * (o) global/bdi setpoints + * + * We want the dirty pages be balanced around the global/bdi setpoints. + * When the number of dirty pages is higher/lower than the setpoint, the + * dirty position control ratio (and hence task dirty ratelimit) will be + * decreased/increased to bring the dirty pages back to the setpoint. + * + * pos_ratio = 1 << RATELIMIT_CALC_SHIFT + * + * if (dirty < setpoint) scale up pos_ratio + * if (dirty > setpoint) scale down pos_ratio + * + * if (bdi_dirty < bdi_setpoint) scale up pos_ratio + * if (bdi_dirty > bdi_setpoint) scale down pos_ratio + * + * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT + * + * (o) global control line + * + * ^ pos_ratio + * | + * | |<===== global dirty control scope ======>| + * 2.0 .............* + * | .* + * | . * + * | . * + * | . * + * | . * + * | . * + * 1.0 ................................* + * | . . * + * | . . * + * | . . * + * | . . * + * | . . * + * 0 +------------.------------------.----------------------*-------------> + * freerun^ setpoint^ limit^ dirty pages + * + * (o) bdi control line + * + * ^ pos_ratio + * | + * | * + * | * + * | * + * | * + * | * |<=========== span ============>| + * 1.0 .......................* + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * 1/4 ...............................................* * * * * * * * * * * * + * | . . + * | . . + * | . . + * 0 +----------------------.-------------------------------.-------------> + * bdi_setpoint^ x_intercept^ + * + * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can + * be smoothly throttled down to normal if it starts high in situations like + * - start writing to a slow SD card and a fast disk at the same time. The SD + * card's bdi_dirty may rush to many times higher than bdi_setpoint. + * - the bdi dirty thresh drops quickly due to change of JBOD workload + */ +static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, + unsigned long thresh, + unsigned long bg_thresh, + unsigned long dirty, + unsigned long bdi_thresh, + unsigned long bdi_dirty) +{ + unsigned long write_bw = bdi->avg_write_bandwidth; + unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); + unsigned long limit = hard_dirty_limit(thresh); + unsigned long x_intercept; + unsigned long setpoint; /* dirty pages' target balance point */ + unsigned long bdi_setpoint; + unsigned long span; + long long pos_ratio; /* for scaling up/down the rate limit */ + long x; + + if (unlikely(dirty >= limit)) + return 0; + + /* + * global setpoint + * + * See comment for pos_ratio_polynom(). + */ + setpoint = (freerun + limit) / 2; + pos_ratio = pos_ratio_polynom(setpoint, dirty, limit); + + /* + * The strictlimit feature is a tool preventing mistrusted filesystems + * from growing a large number of dirty pages before throttling. For + * such filesystems balance_dirty_pages always checks bdi counters + * against bdi limits. Even if global "nr_dirty" is under "freerun". + * This is especially important for fuse which sets bdi->max_ratio to + * 1% by default. Without strictlimit feature, fuse writeback may + * consume arbitrary amount of RAM because it is accounted in + * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". + * + * Here, in bdi_position_ratio(), we calculate pos_ratio based on + * two values: bdi_dirty and bdi_thresh. Let's consider an example: + * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global + * limits are set by default to 10% and 20% (background and throttle). + * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. + * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is + * about ~6K pages (as the average of background and throttle bdi + * limits). The 3rd order polynomial will provide positive feedback if + * bdi_dirty is under bdi_setpoint and vice versa. + * + * Note, that we cannot use global counters in these calculations + * because we want to throttle process writing to a strictlimit BDI + * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB + * in the example above). + */ + if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) { + long long bdi_pos_ratio; + unsigned long bdi_bg_thresh; + + if (bdi_dirty < 8) + return min_t(long long, pos_ratio * 2, + 2 << RATELIMIT_CALC_SHIFT); + + if (bdi_dirty >= bdi_thresh) + return 0; + + bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh); + bdi_setpoint = dirty_freerun_ceiling(bdi_thresh, + bdi_bg_thresh); + + if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh) + return 0; + + bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty, + bdi_thresh); + + /* + * Typically, for strictlimit case, bdi_setpoint << setpoint + * and pos_ratio >> bdi_pos_ratio. In the other words global + * state ("dirty") is not limiting factor and we have to + * make decision based on bdi counters. But there is an + * important case when global pos_ratio should get precedence: + * global limits are exceeded (e.g. due to activities on other + * BDIs) while given strictlimit BDI is below limit. + * + * "pos_ratio * bdi_pos_ratio" would work for the case above, + * but it would look too non-natural for the case of all + * activity in the system coming from a single strictlimit BDI + * with bdi->max_ratio == 100%. + * + * Note that min() below somewhat changes the dynamics of the + * control system. Normally, pos_ratio value can be well over 3 + * (when globally we are at freerun and bdi is well below bdi + * setpoint). Now the maximum pos_ratio in the same situation + * is 2. We might want to tweak this if we observe the control + * system is too slow to adapt. + */ + return min(pos_ratio, bdi_pos_ratio); + } + + /* + * We have computed basic pos_ratio above based on global situation. If + * the bdi is over/under its share of dirty pages, we want to scale + * pos_ratio further down/up. That is done by the following mechanism. + */ + + /* + * bdi setpoint + * + * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) + * + * x_intercept - bdi_dirty + * := -------------------------- + * x_intercept - bdi_setpoint + * + * The main bdi control line is a linear function that subjects to + * + * (1) f(bdi_setpoint) = 1.0 + * (2) k = - 1 / (8 * write_bw) (in single bdi case) + * or equally: x_intercept = bdi_setpoint + 8 * write_bw + * + * For single bdi case, the dirty pages are observed to fluctuate + * regularly within range + * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] + * for various filesystems, where (2) can yield in a reasonable 12.5% + * fluctuation range for pos_ratio. + * + * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its + * own size, so move the slope over accordingly and choose a slope that + * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. + */ + if (unlikely(bdi_thresh > thresh)) + bdi_thresh = thresh; + /* + * It's very possible that bdi_thresh is close to 0 not because the + * device is slow, but that it has remained inactive for long time. + * Honour such devices a reasonable good (hopefully IO efficient) + * threshold, so that the occasional writes won't be blocked and active + * writes can rampup the threshold quickly. + */ + bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); + /* + * scale global setpoint to bdi's: + * bdi_setpoint = setpoint * bdi_thresh / thresh + */ + x = div_u64((u64)bdi_thresh << 16, thresh | 1); + bdi_setpoint = setpoint * (u64)x >> 16; + /* + * Use span=(8*write_bw) in single bdi case as indicated by + * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. + * + * bdi_thresh thresh - bdi_thresh + * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh + * thresh thresh + */ + span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; + x_intercept = bdi_setpoint + span; + + if (bdi_dirty < x_intercept - span / 4) { + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), + (x_intercept - bdi_setpoint) | 1); + } else + pos_ratio /= 4; + + /* + * bdi reserve area, safeguard against dirty pool underrun and disk idle + * It may push the desired control point of global dirty pages higher + * than setpoint. + */ + x_intercept = bdi_thresh / 2; + if (bdi_dirty < x_intercept) { + if (bdi_dirty > x_intercept / 8) + pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); + else + pos_ratio *= 8; + } + + return pos_ratio; +} + +static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, + unsigned long elapsed, + unsigned long written) +{ + const unsigned long period = roundup_pow_of_two(3 * HZ); + unsigned long avg = bdi->avg_write_bandwidth; + unsigned long old = bdi->write_bandwidth; + u64 bw; + + /* + * bw = written * HZ / elapsed + * + * bw * elapsed + write_bandwidth * (period - elapsed) + * write_bandwidth = --------------------------------------------------- + * period + * + * @written may have decreased due to account_page_redirty(). + * Avoid underflowing @bw calculation. + */ + bw = written - min(written, bdi->written_stamp); + bw *= HZ; + if (unlikely(elapsed > period)) { + do_div(bw, elapsed); + avg = bw; + goto out; + } + bw += (u64)bdi->write_bandwidth * (period - elapsed); + bw >>= ilog2(period); + + /* + * one more level of smoothing, for filtering out sudden spikes + */ + if (avg > old && old >= (unsigned long)bw) + avg -= (avg - old) >> 3; + + if (avg < old && old <= (unsigned long)bw) + avg += (old - avg) >> 3; + +out: + bdi->write_bandwidth = bw; + bdi->avg_write_bandwidth = avg; +} + +/* + * The global dirtyable memory and dirty threshold could be suddenly knocked + * down by a large amount (eg. on the startup of KVM in a swapless system). + * This may throw the system into deep dirty exceeded state and throttle + * heavy/light dirtiers alike. To retain good responsiveness, maintain + * global_dirty_limit for tracking slowly down to the knocked down dirty + * threshold. + */ +static void update_dirty_limit(unsigned long thresh, unsigned long dirty) +{ + unsigned long limit = global_dirty_limit; + + /* + * Follow up in one step. + */ + if (limit < thresh) { + limit = thresh; + goto update; + } + + /* + * Follow down slowly. Use the higher one as the target, because thresh + * may drop below dirty. This is exactly the reason to introduce + * global_dirty_limit which is guaranteed to lie above the dirty pages. + */ + thresh = max(thresh, dirty); + if (limit > thresh) { + limit -= (limit - thresh) >> 5; + goto update; + } + return; +update: + global_dirty_limit = limit; +} + +static void global_update_bandwidth(unsigned long thresh, + unsigned long dirty, + unsigned long now) +{ + static DEFINE_SPINLOCK(dirty_lock); + static unsigned long update_time = INITIAL_JIFFIES; + + /* + * check locklessly first to optimize away locking for the most time + */ + if (time_before(now, update_time + BANDWIDTH_INTERVAL)) + return; + + spin_lock(&dirty_lock); + if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { + update_dirty_limit(thresh, dirty); + update_time = now; + } + spin_unlock(&dirty_lock); +} + +/* + * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. + * + * Normal bdi tasks will be curbed at or below it in long term. + * Obviously it should be around (write_bw / N) when there are N dd tasks. + */ +static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, + unsigned long thresh, + unsigned long bg_thresh, + unsigned long dirty, + unsigned long bdi_thresh, + unsigned long bdi_dirty, + unsigned long dirtied, + unsigned long elapsed) +{ + unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); + unsigned long limit = hard_dirty_limit(thresh); + unsigned long setpoint = (freerun + limit) / 2; + unsigned long write_bw = bdi->avg_write_bandwidth; + unsigned long dirty_ratelimit = bdi->dirty_ratelimit; + unsigned long dirty_rate; + unsigned long task_ratelimit; + unsigned long balanced_dirty_ratelimit; + unsigned long pos_ratio; + unsigned long step; + unsigned long x; + + /* + * The dirty rate will match the writeout rate in long term, except + * when dirty pages are truncated by userspace or re-dirtied by FS. + */ + dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; + + pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, + bdi_thresh, bdi_dirty); + /* + * task_ratelimit reflects each dd's dirty rate for the past 200ms. + */ + task_ratelimit = (u64)dirty_ratelimit * + pos_ratio >> RATELIMIT_CALC_SHIFT; + task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ + + /* + * A linear estimation of the "balanced" throttle rate. The theory is, + * if there are N dd tasks, each throttled at task_ratelimit, the bdi's + * dirty_rate will be measured to be (N * task_ratelimit). So the below + * formula will yield the balanced rate limit (write_bw / N). + * + * Note that the expanded form is not a pure rate feedback: + * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) + * but also takes pos_ratio into account: + * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) + * + * (1) is not realistic because pos_ratio also takes part in balancing + * the dirty rate. Consider the state + * pos_ratio = 0.5 (3) + * rate = 2 * (write_bw / N) (4) + * If (1) is used, it will stuck in that state! Because each dd will + * be throttled at + * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) + * yielding + * dirty_rate = N * task_ratelimit = write_bw (6) + * put (6) into (1) we get + * rate_(i+1) = rate_(i) (7) + * + * So we end up using (2) to always keep + * rate_(i+1) ~= (write_bw / N) (8) + * regardless of the value of pos_ratio. As long as (8) is satisfied, + * pos_ratio is able to drive itself to 1.0, which is not only where + * the dirty count meet the setpoint, but also where the slope of + * pos_ratio is most flat and hence task_ratelimit is least fluctuated. + */ + balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, + dirty_rate | 1); + /* + * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw + */ + if (unlikely(balanced_dirty_ratelimit > write_bw)) + balanced_dirty_ratelimit = write_bw; + + /* + * We could safely do this and return immediately: + * + * bdi->dirty_ratelimit = balanced_dirty_ratelimit; + * + * However to get a more stable dirty_ratelimit, the below elaborated + * code makes use of task_ratelimit to filter out singular points and + * limit the step size. + * + * The below code essentially only uses the relative value of + * + * task_ratelimit - dirty_ratelimit + * = (pos_ratio - 1) * dirty_ratelimit + * + * which reflects the direction and size of dirty position error. + */ + + /* + * dirty_ratelimit will follow balanced_dirty_ratelimit iff + * task_ratelimit is on the same side of dirty_ratelimit, too. + * For example, when + * - dirty_ratelimit > balanced_dirty_ratelimit + * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) + * lowering dirty_ratelimit will help meet both the position and rate + * control targets. Otherwise, don't update dirty_ratelimit if it will + * only help meet the rate target. After all, what the users ultimately + * feel and care are stable dirty rate and small position error. + * + * |task_ratelimit - dirty_ratelimit| is used to limit the step size + * and filter out the singular points of balanced_dirty_ratelimit. Which + * keeps jumping around randomly and can even leap far away at times + * due to the small 200ms estimation period of dirty_rate (we want to + * keep that period small to reduce time lags). + */ + step = 0; + + /* + * For strictlimit case, calculations above were based on bdi counters + * and limits (starting from pos_ratio = bdi_position_ratio() and up to + * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). + * Hence, to calculate "step" properly, we have to use bdi_dirty as + * "dirty" and bdi_setpoint as "setpoint". + * + * We rampup dirty_ratelimit forcibly if bdi_dirty is low because + * it's possible that bdi_thresh is close to zero due to inactivity + * of backing device (see the implementation of bdi_dirty_limit()). + */ + if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) { + dirty = bdi_dirty; + if (bdi_dirty < 8) + setpoint = bdi_dirty + 1; + else + setpoint = (bdi_thresh + + bdi_dirty_limit(bdi, bg_thresh)) / 2; + } + + if (dirty < setpoint) { + x = min3(bdi->balanced_dirty_ratelimit, + balanced_dirty_ratelimit, task_ratelimit); + if (dirty_ratelimit < x) + step = x - dirty_ratelimit; + } else { + x = max3(bdi->balanced_dirty_ratelimit, + balanced_dirty_ratelimit, task_ratelimit); + if (dirty_ratelimit > x) + step = dirty_ratelimit - x; + } + + /* + * Don't pursue 100% rate matching. It's impossible since the balanced + * rate itself is constantly fluctuating. So decrease the track speed + * when it gets close to the target. Helps eliminate pointless tremors. + */ + step >>= dirty_ratelimit / (2 * step + 1); + /* + * Limit the tracking speed to avoid overshooting. + */ + step = (step + 7) / 8; + + if (dirty_ratelimit < balanced_dirty_ratelimit) + dirty_ratelimit += step; + else + dirty_ratelimit -= step; + + bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); + bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; + + trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); +} + +void __bdi_update_bandwidth(struct backing_dev_info *bdi, + unsigned long thresh, + unsigned long bg_thresh, + unsigned long dirty, + unsigned long bdi_thresh, + unsigned long bdi_dirty, + unsigned long start_time) +{ + unsigned long now = jiffies; + unsigned long elapsed = now - bdi->bw_time_stamp; + unsigned long dirtied; + unsigned long written; + + /* + * rate-limit, only update once every 200ms. + */ + if (elapsed < BANDWIDTH_INTERVAL) + return; + + dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); + written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); + + /* + * Skip quiet periods when disk bandwidth is under-utilized. + * (at least 1s idle time between two flusher runs) + */ + if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) + goto snapshot; + + if (thresh) { + global_update_bandwidth(thresh, dirty, now); + bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, + bdi_thresh, bdi_dirty, + dirtied, elapsed); + } + bdi_update_write_bandwidth(bdi, elapsed, written); + +snapshot: + bdi->dirtied_stamp = dirtied; + bdi->written_stamp = written; + bdi->bw_time_stamp = now; +} + +static void bdi_update_bandwidth(struct backing_dev_info *bdi, + unsigned long thresh, + unsigned long bg_thresh, + unsigned long dirty, + unsigned long bdi_thresh, + unsigned long bdi_dirty, + unsigned long start_time) +{ + if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) + return; + spin_lock(&bdi->wb.list_lock); + __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, + bdi_thresh, bdi_dirty, start_time); + spin_unlock(&bdi->wb.list_lock); +} + +/* + * After a task dirtied this many pages, balance_dirty_pages_ratelimited() + * will look to see if it needs to start dirty throttling. + * + * If dirty_poll_interval is too low, big NUMA machines will call the expensive + * global_page_state() too often. So scale it near-sqrt to the safety margin + * (the number of pages we may dirty without exceeding the dirty limits). + */ +static unsigned long dirty_poll_interval(unsigned long dirty, + unsigned long thresh) +{ + if (thresh > dirty) + return 1UL << (ilog2(thresh - dirty) >> 1); + + return 1; +} + +static unsigned long bdi_max_pause(struct backing_dev_info *bdi, + unsigned long bdi_dirty) +{ + unsigned long bw = bdi->avg_write_bandwidth; + unsigned long t; + + /* + * Limit pause time for small memory systems. If sleeping for too long + * time, a small pool of dirty/writeback pages may go empty and disk go + * idle. + * + * 8 serves as the safety ratio. + */ + t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); + t++; + + return min_t(unsigned long, t, MAX_PAUSE); +} + +static long bdi_min_pause(struct backing_dev_info *bdi, + long max_pause, + unsigned long task_ratelimit, + unsigned long dirty_ratelimit, + int *nr_dirtied_pause) +{ + long hi = ilog2(bdi->avg_write_bandwidth); + long lo = ilog2(bdi->dirty_ratelimit); + long t; /* target pause */ + long pause; /* estimated next pause */ + int pages; /* target nr_dirtied_pause */ + + /* target for 10ms pause on 1-dd case */ + t = max(1, HZ / 100); + + /* + * Scale up pause time for concurrent dirtiers in order to reduce CPU + * overheads. + * + * (N * 10ms) on 2^N concurrent tasks. + */ + if (hi > lo) + t += (hi - lo) * (10 * HZ) / 1024; + + /* + * This is a bit convoluted. We try to base the next nr_dirtied_pause + * on the much more stable dirty_ratelimit. However the next pause time + * will be computed based on task_ratelimit and the two rate limits may + * depart considerably at some time. Especially if task_ratelimit goes + * below dirty_ratelimit/2 and the target pause is max_pause, the next + * pause time will be max_pause*2 _trimmed down_ to max_pause. As a + * result task_ratelimit won't be executed faithfully, which could + * eventually bring down dirty_ratelimit. + * + * We apply two rules to fix it up: + * 1) try to estimate the next pause time and if necessary, use a lower + * nr_dirtied_pause so as not to exceed max_pause. When this happens, + * nr_dirtied_pause will be "dancing" with task_ratelimit. + * 2) limit the target pause time to max_pause/2, so that the normal + * small fluctuations of task_ratelimit won't trigger rule (1) and + * nr_dirtied_pause will remain as stable as dirty_ratelimit. + */ + t = min(t, 1 + max_pause / 2); + pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); + + /* + * Tiny nr_dirtied_pause is found to hurt I/O performance in the test + * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. + * When the 16 consecutive reads are often interrupted by some dirty + * throttling pause during the async writes, cfq will go into idles + * (deadline is fine). So push nr_dirtied_pause as high as possible + * until reaches DIRTY_POLL_THRESH=32 pages. + */ + if (pages < DIRTY_POLL_THRESH) { + t = max_pause; + pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); + if (pages > DIRTY_POLL_THRESH) { + pages = DIRTY_POLL_THRESH; + t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; + } + } + + pause = HZ * pages / (task_ratelimit + 1); + if (pause > max_pause) { + t = max_pause; + pages = task_ratelimit * t / roundup_pow_of_two(HZ); + } + + *nr_dirtied_pause = pages; + /* + * The minimal pause time will normally be half the target pause time. + */ + return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; +} + +static inline void bdi_dirty_limits(struct backing_dev_info *bdi, + unsigned long dirty_thresh, + unsigned long background_thresh, + unsigned long *bdi_dirty, + unsigned long *bdi_thresh, + unsigned long *bdi_bg_thresh) +{ + unsigned long bdi_reclaimable; + + /* + * bdi_thresh is not treated as some limiting factor as + * dirty_thresh, due to reasons + * - in JBOD setup, bdi_thresh can fluctuate a lot + * - in a system with HDD and USB key, the USB key may somehow + * go into state (bdi_dirty >> bdi_thresh) either because + * bdi_dirty starts high, or because bdi_thresh drops low. + * In this case we don't want to hard throttle the USB key + * dirtiers for 100 seconds until bdi_dirty drops under + * bdi_thresh. Instead the auxiliary bdi control line in + * bdi_position_ratio() will let the dirtier task progress + * at some rate <= (write_bw / 2) for bringing down bdi_dirty. + */ + *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); + + if (bdi_bg_thresh) + *bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh * + background_thresh, + dirty_thresh) : 0; + + /* + * 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_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); + *bdi_dirty = bdi_reclaimable + + bdi_stat_sum(bdi, BDI_WRITEBACK); + } else { + bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); + *bdi_dirty = bdi_reclaimable + + bdi_stat(bdi, BDI_WRITEBACK); + } +} + +/* + * 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 wait once crossing the (background_thresh + dirty_thresh) / 2. + * 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 pages_dirtied) +{ + unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ + unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ + unsigned long background_thresh; + unsigned long dirty_thresh; + long period; + long pause; + long max_pause; + long min_pause; + int nr_dirtied_pause; + bool dirty_exceeded = false; + unsigned long task_ratelimit; + unsigned long dirty_ratelimit; + unsigned long pos_ratio; + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; + unsigned long start_time = jiffies; + + for (;;) { + unsigned long now = jiffies; + unsigned long uninitialized_var(bdi_thresh); + unsigned long thresh; + unsigned long uninitialized_var(bdi_dirty); + unsigned long dirty; + unsigned long bg_thresh; + + /* + * 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. + */ + nr_reclaimable = global_page_state(NR_FILE_DIRTY) + + global_page_state(NR_UNSTABLE_NFS); + nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); + + global_dirty_limits(&background_thresh, &dirty_thresh); + + if (unlikely(strictlimit)) { + bdi_dirty_limits(bdi, dirty_thresh, background_thresh, + &bdi_dirty, &bdi_thresh, &bg_thresh); + + dirty = bdi_dirty; + thresh = bdi_thresh; + } else { + dirty = nr_dirty; + thresh = dirty_thresh; + bg_thresh = background_thresh; + } + + /* + * Throttle it only when the background writeback cannot + * catch-up. This avoids (excessively) small writeouts + * when the bdi limits are ramping up in case of !strictlimit. + * + * In strictlimit case make decision based on the bdi counters + * and limits. Small writeouts when the bdi limits are ramping + * up are the price we consciously pay for strictlimit-ing. + */ + if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) { + current->dirty_paused_when = now; + current->nr_dirtied = 0; + current->nr_dirtied_pause = + dirty_poll_interval(dirty, thresh); + break; + } + + if (unlikely(!writeback_in_progress(bdi))) + bdi_start_background_writeback(bdi); + + if (!strictlimit) + bdi_dirty_limits(bdi, dirty_thresh, background_thresh, + &bdi_dirty, &bdi_thresh, NULL); + + dirty_exceeded = (bdi_dirty > bdi_thresh) && + ((nr_dirty > dirty_thresh) || strictlimit); + if (dirty_exceeded && !bdi->dirty_exceeded) + bdi->dirty_exceeded = 1; + + bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, + nr_dirty, bdi_thresh, bdi_dirty, + start_time); + + dirty_ratelimit = bdi->dirty_ratelimit; + pos_ratio = bdi_position_ratio(bdi, dirty_thresh, + background_thresh, nr_dirty, + bdi_thresh, bdi_dirty); + task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> + RATELIMIT_CALC_SHIFT; + max_pause = bdi_max_pause(bdi, bdi_dirty); + min_pause = bdi_min_pause(bdi, max_pause, + task_ratelimit, dirty_ratelimit, + &nr_dirtied_pause); + + if (unlikely(task_ratelimit == 0)) { + period = max_pause; + pause = max_pause; + goto pause; + } + period = HZ * pages_dirtied / task_ratelimit; + pause = period; + if (current->dirty_paused_when) + pause -= now - current->dirty_paused_when; + /* + * For less than 1s think time (ext3/4 may block the dirtier + * for up to 800ms from time to time on 1-HDD; so does xfs, + * however at much less frequency), try to compensate it in + * future periods by updating the virtual time; otherwise just + * do a reset, as it may be a light dirtier. + */ + if (pause < min_pause) { + trace_balance_dirty_pages(bdi, + dirty_thresh, + background_thresh, + nr_dirty, + bdi_thresh, + bdi_dirty, + dirty_ratelimit, + task_ratelimit, + pages_dirtied, + period, + min(pause, 0L), + start_time); + if (pause < -HZ) { + current->dirty_paused_when = now; + current->nr_dirtied = 0; + } else if (period) { + current->dirty_paused_when += period; + current->nr_dirtied = 0; + } else if (current->nr_dirtied_pause <= pages_dirtied) + current->nr_dirtied_pause += pages_dirtied; + break; + } + if (unlikely(pause > max_pause)) { + /* for occasional dropped task_ratelimit */ + now += min(pause - max_pause, max_pause); + pause = max_pause; + } + +pause: + trace_balance_dirty_pages(bdi, + dirty_thresh, + background_thresh, + nr_dirty, + bdi_thresh, + bdi_dirty, + dirty_ratelimit, + task_ratelimit, + pages_dirtied, + period, + pause, + start_time); + __set_current_state(TASK_KILLABLE); + io_schedule_timeout(pause); + + current->dirty_paused_when = now + pause; + current->nr_dirtied = 0; + current->nr_dirtied_pause = nr_dirtied_pause; + + /* + * This is typically equal to (nr_dirty < dirty_thresh) and can + * also keep "1000+ dd on a slow USB stick" under control. + */ + if (task_ratelimit) + break; + + /* + * In the case of an unresponding NFS server and the NFS dirty + * pages exceeds dirty_thresh, give the other good bdi's a pipe + * to go through, so that tasks on them still remain responsive. + * + * In theory 1 page is enough to keep the comsumer-producer + * pipe going: the flusher cleans 1 page => the task dirties 1 + * more page. However bdi_dirty has accounting errors. So use + * the larger and more IO friendly bdi_stat_error. + */ + if (bdi_dirty <= bdi_stat_error(bdi)) + break; + + if (fatal_signal_pending(current)) + break; + } + + 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) + return; + + if (nr_reclaimable > background_thresh) + bdi_start_background_writeback(bdi); +} + +static DEFINE_PER_CPU(int, bdp_ratelimits); + +/* + * Normal tasks are throttled by + * loop { + * dirty tsk->nr_dirtied_pause pages; + * take a snap in balance_dirty_pages(); + * } + * However there is a worst case. If every task exit immediately when dirtied + * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be + * called to throttle the page dirties. The solution is to save the not yet + * throttled page dirties in dirty_throttle_leaks on task exit and charge them + * randomly into the running tasks. This works well for the above worst case, + * as the new task will pick up and accumulate the old task's leaked dirty + * count and eventually get throttled. + */ +DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; + +/** + * balance_dirty_pages_ratelimited - balance dirty memory state + * @mapping: address_space which was 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(struct address_space *mapping) +{ + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + int ratelimit; + int *p; + + if (!bdi_cap_account_dirty(bdi)) + return; + + ratelimit = current->nr_dirtied_pause; + if (bdi->dirty_exceeded) + ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); + + preempt_disable(); + /* + * This prevents one CPU to accumulate too many dirtied pages without + * calling into balance_dirty_pages(), which can happen when there are + * 1000+ tasks, all of them start dirtying pages at exactly the same + * time, hence all honoured too large initial task->nr_dirtied_pause. + */ + p = this_cpu_ptr(&bdp_ratelimits); + if (unlikely(current->nr_dirtied >= ratelimit)) + *p = 0; + else if (unlikely(*p >= ratelimit_pages)) { + *p = 0; + ratelimit = 0; + } + /* + * Pick up the dirtied pages by the exited tasks. This avoids lots of + * short-lived tasks (eg. gcc invocations in a kernel build) escaping + * the dirty throttling and livelock other long-run dirtiers. + */ + p = this_cpu_ptr(&dirty_throttle_leaks); + if (*p > 0 && current->nr_dirtied < ratelimit) { + unsigned long nr_pages_dirtied; + nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); + *p -= nr_pages_dirtied; + current->nr_dirtied += nr_pages_dirtied; + } + preempt_enable(); + + if (unlikely(current->nr_dirtied >= ratelimit)) + balance_dirty_pages(mapping, current->nr_dirtied); +} +EXPORT_SYMBOL(balance_dirty_pages_ratelimited); + +void throttle_vm_writeout(gfp_t gfp_mask) +{ + unsigned long background_thresh; + unsigned long dirty_thresh; + + for ( ; ; ) { + global_dirty_limits(&background_thresh, &dirty_thresh); + dirty_thresh = hard_dirty_limit(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(struct ctl_table *table, int write, + void __user *buffer, size_t *length, loff_t *ppos) +{ + proc_dointvec(table, write, buffer, length, ppos); + 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, + WB_REASON_LAPTOP_TIMER); +} + +/* + * 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. + */ + +void writeback_set_ratelimit(void) +{ + unsigned long background_thresh; + unsigned long dirty_thresh; + global_dirty_limits(&background_thresh, &dirty_thresh); + global_dirty_limit = dirty_thresh; + ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); + if (ratelimit_pages < 16) + ratelimit_pages = 16; +} + +static int +ratelimit_handler(struct notifier_block *self, unsigned long action, + void *hcpu) +{ + + switch (action & ~CPU_TASKS_FROZEN) { + case CPU_ONLINE: + case CPU_DEAD: + writeback_set_ratelimit(); + return NOTIFY_OK; + default: + return NOTIFY_DONE; + } +} + +static struct notifier_block 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) +{ + writeback_set_ratelimit(); + register_cpu_notifier(&ratelimit_nb); + + fprop_global_init(&writeout_completions, GFP_KERNEL); +} + +/** + * 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, inode_to_bdi(mapping->host)); + 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) +{ + trace_writeback_dirty_page(page, mapping); + + if (mapping_cap_account_dirty(mapping)) { + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + + __inc_zone_page_state(page, NR_FILE_DIRTY); + __inc_zone_page_state(page, NR_DIRTIED); + __inc_bdi_stat(bdi, BDI_RECLAIMABLE); + __inc_bdi_stat(bdi, BDI_DIRTIED); + task_io_account_write(PAGE_CACHE_SIZE); + current->nr_dirtied++; + this_cpu_inc(bdp_ratelimits); + } +} +EXPORT_SYMBOL(account_page_dirtied); + +/* + * Helper function for deaccounting dirty page without writeback. + * + * Doing this should *normally* only ever be done when a page + * is truncated, and is not actually mapped anywhere at all. However, + * fs/buffer.c does this when it notices that somebody has cleaned + * out all the buffers on a page without actually doing it through + * the VM. Can you say "ext3 is horribly ugly"? Thought you could. + */ +void account_page_cleaned(struct page *page, struct address_space *mapping) +{ + if (mapping_cap_account_dirty(mapping)) { + dec_zone_page_state(page, NR_FILE_DIRTY); + dec_bdi_stat(inode_to_bdi(mapping->host), BDI_RECLAIMABLE); + task_io_account_cancelled_write(PAGE_CACHE_SIZE); + } +} +EXPORT_SYMBOL(account_page_cleaned); + +/* + * 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. + * + * The caller must ensure this doesn't race with truncation. Most will simply + * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and + * the pte lock held, which also locks out truncation. + */ +int __set_page_dirty_nobuffers(struct page *page) +{ + if (!TestSetPageDirty(page)) { + struct address_space *mapping = page_mapping(page); + unsigned long flags; + + if (!mapping) + return 1; + + spin_lock_irqsave(&mapping->tree_lock, flags); + BUG_ON(page_mapping(page) != 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_irqrestore(&mapping->tree_lock, flags); + if (mapping->host) { + /* !PageAnon && !swapper_space */ + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); + } + return 1; + } + return 0; +} +EXPORT_SYMBOL(__set_page_dirty_nobuffers); + +/* + * Call this whenever redirtying a page, to de-account the dirty counters + * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written + * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to + * systematic errors in balanced_dirty_ratelimit and the dirty pages position + * control. + */ +void account_page_redirty(struct page *page) +{ + struct address_space *mapping = page->mapping; + if (mapping && mapping_cap_account_dirty(mapping)) { + current->nr_dirtied--; + dec_zone_page_state(page, NR_DIRTIED); + dec_bdi_stat(inode_to_bdi(mapping->host), BDI_DIRTIED); + } +} +EXPORT_SYMBOL(account_page_redirty); + +/* + * 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) +{ + int ret; + + wbc->pages_skipped++; + ret = __set_page_dirty_nobuffers(page); + account_page_redirty(page); + return ret; +} +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. + */ + if (PageReclaim(page)) + 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 while dirtying the page, and pages are + * always locked coming in here, so we get the desired + * exclusion. + */ + if (TestClearPageDirty(page)) { + dec_zone_page_state(page, NR_FILE_DIRTY); + dec_bdi_stat(inode_to_bdi(mapping->host), + 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); + struct mem_cgroup *memcg; + int ret; + + memcg = mem_cgroup_begin_page_stat(page); + if (mapping) { + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + 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) { + mem_cgroup_dec_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK); + dec_zone_page_state(page, NR_WRITEBACK); + inc_zone_page_state(page, NR_WRITTEN); + } + mem_cgroup_end_page_stat(memcg); + return ret; +} + +int __test_set_page_writeback(struct page *page, bool keep_write) +{ + struct address_space *mapping = page_mapping(page); + struct mem_cgroup *memcg; + int ret; + + memcg = mem_cgroup_begin_page_stat(page); + if (mapping) { + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + 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); + if (!keep_write) + 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) { + mem_cgroup_inc_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK); + inc_zone_page_state(page, NR_WRITEBACK); + } + mem_cgroup_end_page_stat(memcg); + 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) +{ + return radix_tree_tagged(&mapping->page_tree, tag); +} +EXPORT_SYMBOL(mapping_tagged); + +/** + * wait_for_stable_page() - wait for writeback to finish, if necessary. + * @page: The page to wait on. + * + * This function determines if the given page is related to a backing device + * that requires page contents to be held stable during writeback. If so, then + * it will wait for any pending writeback to complete. + */ +void wait_for_stable_page(struct page *page) +{ + if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host))) + wait_on_page_writeback(page); +} +EXPORT_SYMBOL_GPL(wait_for_stable_page); |