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Diffstat (limited to '')
| -rw-r--r-- | mm/page-writeback.c | 3084 |
1 files changed, 3084 insertions, 0 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c new file mode 100644 index 000000000..de5f69921 --- /dev/null +++ b/mm/page-writeback.c @@ -0,0 +1,3084 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * mm/page-writeback.c + * + * Copyright (C) 2002, Linus Torvalds. + * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra + * + * 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/smp.h> +#include <linux/sysctl.h> +#include <linux/cpu.h> +#include <linux/syscalls.h> +#include <linux/pagevec.h> +#include <linux/timer.h> +#include <linux/sched/rt.h> +#include <linux/sched/signal.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 + */ +static 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 + */ +static 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 + */ +static int vm_highmem_is_dirtyable; + +/* + * The generator of dirty data starts writeback at this percentage + */ +static 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 + */ +static 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 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 */ + +struct wb_domain global_wb_domain; + +/* consolidated parameters for balance_dirty_pages() and its subroutines */ +struct dirty_throttle_control { +#ifdef CONFIG_CGROUP_WRITEBACK + struct wb_domain *dom; + struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */ +#endif + struct bdi_writeback *wb; + struct fprop_local_percpu *wb_completions; + + unsigned long avail; /* dirtyable */ + unsigned long dirty; /* file_dirty + write + nfs */ + unsigned long thresh; /* dirty threshold */ + unsigned long bg_thresh; /* dirty background threshold */ + + unsigned long wb_dirty; /* per-wb counterparts */ + unsigned long wb_thresh; + unsigned long wb_bg_thresh; + + unsigned long pos_ratio; +}; + +/* + * 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) + +#ifdef CONFIG_CGROUP_WRITEBACK + +#define GDTC_INIT(__wb) .wb = (__wb), \ + .dom = &global_wb_domain, \ + .wb_completions = &(__wb)->completions + +#define GDTC_INIT_NO_WB .dom = &global_wb_domain + +#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \ + .dom = mem_cgroup_wb_domain(__wb), \ + .wb_completions = &(__wb)->memcg_completions, \ + .gdtc = __gdtc + +static bool mdtc_valid(struct dirty_throttle_control *dtc) +{ + return dtc->dom; +} + +static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) +{ + return dtc->dom; +} + +static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) +{ + return mdtc->gdtc; +} + +static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) +{ + return &wb->memcg_completions; +} + +static void wb_min_max_ratio(struct bdi_writeback *wb, + unsigned long *minp, unsigned long *maxp) +{ + unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth); + unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth); + unsigned long long min = wb->bdi->min_ratio; + unsigned long long max = wb->bdi->max_ratio; + + /* + * @wb may already be clean by the time control reaches here and + * the total may not include its bw. + */ + if (this_bw < tot_bw) { + if (min) { + min *= this_bw; + min = div64_ul(min, tot_bw); + } + if (max < 100) { + max *= this_bw; + max = div64_ul(max, tot_bw); + } + } + + *minp = min; + *maxp = max; +} + +#else /* CONFIG_CGROUP_WRITEBACK */ + +#define GDTC_INIT(__wb) .wb = (__wb), \ + .wb_completions = &(__wb)->completions +#define GDTC_INIT_NO_WB +#define MDTC_INIT(__wb, __gdtc) + +static bool mdtc_valid(struct dirty_throttle_control *dtc) +{ + return false; +} + +static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) +{ + return &global_wb_domain; +} + +static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) +{ + return NULL; +} + +static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) +{ + return NULL; +} + +static void wb_min_max_ratio(struct bdi_writeback *wb, + unsigned long *minp, unsigned long *maxp) +{ + *minp = wb->bdi->min_ratio; + *maxp = wb->bdi->max_ratio; +} + +#endif /* CONFIG_CGROUP_WRITEBACK */ + +/* + * 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 effective 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. + */ + +/** + * node_dirtyable_memory - number of dirtyable pages in a node + * @pgdat: the node + * + * Return: the node's number of pages potentially available for dirty + * page cache. This is the base value for the per-node dirty limits. + */ +static unsigned long node_dirtyable_memory(struct pglist_data *pgdat) +{ + unsigned long nr_pages = 0; + int z; + + for (z = 0; z < MAX_NR_ZONES; z++) { + struct zone *zone = pgdat->node_zones + z; + + if (!populated_zone(zone)) + continue; + + nr_pages += zone_page_state(zone, NR_FREE_PAGES); + } + + /* + * Pages reserved for the kernel should not be considered + * dirtyable, to prevent a situation where reclaim has to + * clean pages in order to balance the zones. + */ + nr_pages -= min(nr_pages, pgdat->totalreserve_pages); + + nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE); + nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE); + + return nr_pages; +} + +static unsigned long highmem_dirtyable_memory(unsigned long total) +{ +#ifdef CONFIG_HIGHMEM + int node; + unsigned long x = 0; + int i; + + for_each_node_state(node, N_HIGH_MEMORY) { + for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) { + struct zone *z; + unsigned long nr_pages; + + if (!is_highmem_idx(i)) + continue; + + z = &NODE_DATA(node)->node_zones[i]; + if (!populated_zone(z)) + continue; + + nr_pages = zone_page_state(z, NR_FREE_PAGES); + /* watch for underflows */ + nr_pages -= min(nr_pages, high_wmark_pages(z)); + nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE); + nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE); + x += nr_pages; + } + } + + /* + * 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 + * + * Return: 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_zone_page_state(NR_FREE_PAGES); + /* + * Pages reserved for the kernel should not be considered + * dirtyable, to prevent a situation where reclaim has to + * clean pages in order to balance the zones. + */ + x -= min(x, totalreserve_pages); + + x += global_node_page_state(NR_INACTIVE_FILE); + x += global_node_page_state(NR_ACTIVE_FILE); + + if (!vm_highmem_is_dirtyable) + x -= highmem_dirtyable_memory(x); + + return x + 1; /* Ensure that we never return 0 */ +} + +/** + * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain + * @dtc: dirty_throttle_control of interest + * + * Calculate @dtc->thresh and ->bg_thresh considering + * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller + * must ensure that @dtc->avail is set before calling this function. The + * dirty limits will be lifted by 1/4 for real-time tasks. + */ +static void domain_dirty_limits(struct dirty_throttle_control *dtc) +{ + const unsigned long available_memory = dtc->avail; + struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc); + unsigned long bytes = vm_dirty_bytes; + unsigned long bg_bytes = dirty_background_bytes; + /* convert ratios to per-PAGE_SIZE for higher precision */ + unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; + unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100; + unsigned long thresh; + unsigned long bg_thresh; + struct task_struct *tsk; + + /* gdtc is !NULL iff @dtc is for memcg domain */ + if (gdtc) { + unsigned long global_avail = gdtc->avail; + + /* + * The byte settings can't be applied directly to memcg + * domains. Convert them to ratios by scaling against + * globally available memory. As the ratios are in + * per-PAGE_SIZE, they can be obtained by dividing bytes by + * number of pages. + */ + if (bytes) + ratio = min(DIV_ROUND_UP(bytes, global_avail), + PAGE_SIZE); + if (bg_bytes) + bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail), + PAGE_SIZE); + bytes = bg_bytes = 0; + } + + if (bytes) + thresh = DIV_ROUND_UP(bytes, PAGE_SIZE); + else + thresh = (ratio * available_memory) / PAGE_SIZE; + + if (bg_bytes) + bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE); + else + bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; + + if (bg_thresh >= thresh) + bg_thresh = thresh / 2; + tsk = current; + if (rt_task(tsk)) { + bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32; + thresh += thresh / 4 + global_wb_domain.dirty_limit / 32; + } + dtc->thresh = thresh; + dtc->bg_thresh = bg_thresh; + + /* we should eventually report the domain in the TP */ + if (!gdtc) + trace_global_dirty_state(bg_thresh, thresh); +} + +/** + * global_dirty_limits - background-writeback and dirty-throttling thresholds + * @pbackground: out parameter for bg_thresh + * @pdirty: out parameter for thresh + * + * Calculate bg_thresh and thresh for global_wb_domain. See + * domain_dirty_limits() for details. + */ +void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) +{ + struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB }; + + gdtc.avail = global_dirtyable_memory(); + domain_dirty_limits(&gdtc); + + *pbackground = gdtc.bg_thresh; + *pdirty = gdtc.thresh; +} + +/** + * node_dirty_limit - maximum number of dirty pages allowed in a node + * @pgdat: the node + * + * Return: the maximum number of dirty pages allowed in a node, based + * on the node's dirtyable memory. + */ +static unsigned long node_dirty_limit(struct pglist_data *pgdat) +{ + unsigned long node_memory = node_dirtyable_memory(pgdat); + struct task_struct *tsk = current; + unsigned long dirty; + + if (vm_dirty_bytes) + dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * + node_memory / global_dirtyable_memory(); + else + dirty = vm_dirty_ratio * node_memory / 100; + + if (rt_task(tsk)) + dirty += dirty / 4; + + return dirty; +} + +/** + * node_dirty_ok - tells whether a node is within its dirty limits + * @pgdat: the node to check + * + * Return: %true when the dirty pages in @pgdat are within the node's + * dirty limit, %false if the limit is exceeded. + */ +bool node_dirty_ok(struct pglist_data *pgdat) +{ + unsigned long limit = node_dirty_limit(pgdat); + unsigned long nr_pages = 0; + + nr_pages += node_page_state(pgdat, NR_FILE_DIRTY); + nr_pages += node_page_state(pgdat, NR_WRITEBACK); + + return nr_pages <= limit; +} + +#ifdef CONFIG_SYSCTL +static int dirty_background_ratio_handler(struct ctl_table *table, int write, + void *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; +} + +static int dirty_background_bytes_handler(struct ctl_table *table, int write, + void *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; +} + +static int dirty_ratio_handler(struct ctl_table *table, int write, void *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; +} + +static int dirty_bytes_handler(struct ctl_table *table, int write, + void *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; +} +#endif + +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; +} + +static void wb_domain_writeout_add(struct wb_domain *dom, + struct fprop_local_percpu *completions, + unsigned int max_prop_frac, long nr) +{ + __fprop_add_percpu_max(&dom->completions, completions, + max_prop_frac, nr); + /* First event after period switching was turned off? */ + if (unlikely(!dom->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. + */ + dom->period_time = wp_next_time(jiffies); + mod_timer(&dom->period_timer, dom->period_time); + } +} + +/* + * Increment @wb's writeout completion count and the global writeout + * completion count. Called from __folio_end_writeback(). + */ +static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr) +{ + struct wb_domain *cgdom; + + wb_stat_mod(wb, WB_WRITTEN, nr); + wb_domain_writeout_add(&global_wb_domain, &wb->completions, + wb->bdi->max_prop_frac, nr); + + cgdom = mem_cgroup_wb_domain(wb); + if (cgdom) + wb_domain_writeout_add(cgdom, wb_memcg_completions(wb), + wb->bdi->max_prop_frac, nr); +} + +void wb_writeout_inc(struct bdi_writeback *wb) +{ + unsigned long flags; + + local_irq_save(flags); + __wb_writeout_add(wb, 1); + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(wb_writeout_inc); + +/* + * 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(struct timer_list *t) +{ + struct wb_domain *dom = from_timer(dom, t, period_timer); + int miss_periods = (jiffies - dom->period_time) / + VM_COMPLETIONS_PERIOD_LEN; + + if (fprop_new_period(&dom->completions, miss_periods + 1)) { + dom->period_time = wp_next_time(dom->period_time + + miss_periods * VM_COMPLETIONS_PERIOD_LEN); + mod_timer(&dom->period_timer, dom->period_time); + } else { + /* + * Aging has zeroed all fractions. Stop wasting CPU on period + * updates. + */ + dom->period_time = 0; + } +} + +int wb_domain_init(struct wb_domain *dom, gfp_t gfp) +{ + memset(dom, 0, sizeof(*dom)); + + spin_lock_init(&dom->lock); + + timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE); + + dom->dirty_limit_tstamp = jiffies; + + return fprop_global_init(&dom->completions, gfp); +} + +#ifdef CONFIG_CGROUP_WRITEBACK +void wb_domain_exit(struct wb_domain *dom) +{ + del_timer_sync(&dom->period_timer); + fprop_global_destroy(&dom->completions); +} +#endif + +/* + * 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) +{ + unsigned int delta; + int ret = 0; + + spin_lock_bh(&bdi_lock); + if (min_ratio > bdi->max_ratio) { + ret = -EINVAL; + } else { + if (min_ratio < bdi->min_ratio) { + delta = bdi->min_ratio - min_ratio; + bdi_min_ratio -= delta; + bdi->min_ratio = min_ratio; + } else { + delta = min_ratio - bdi->min_ratio; + if (bdi_min_ratio + delta < 100) { + bdi_min_ratio += delta; + 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(struct wb_domain *dom, + unsigned long thresh) +{ + return max(thresh, dom->dirty_limit); +} + +/* + * Memory which can be further allocated to a memcg domain is capped by + * system-wide clean memory excluding the amount being used in the domain. + */ +static void mdtc_calc_avail(struct dirty_throttle_control *mdtc, + unsigned long filepages, unsigned long headroom) +{ + struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc); + unsigned long clean = filepages - min(filepages, mdtc->dirty); + unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty); + unsigned long other_clean = global_clean - min(global_clean, clean); + + mdtc->avail = filepages + min(headroom, other_clean); +} + +/** + * __wb_calc_thresh - @wb's share of dirty throttling threshold + * @dtc: dirty_throttle_context of interest + * + * 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 wb 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 wb'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. + * + * Return: @wb's dirty limit in pages. The term "dirty" in the context of + * dirty balancing includes all PG_dirty and PG_writeback pages. + */ +static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc) +{ + struct wb_domain *dom = dtc_dom(dtc); + unsigned long thresh = dtc->thresh; + u64 wb_thresh; + unsigned long numerator, denominator; + unsigned long wb_min_ratio, wb_max_ratio; + + /* + * Calculate this BDI's share of the thresh ratio. + */ + fprop_fraction_percpu(&dom->completions, dtc->wb_completions, + &numerator, &denominator); + + wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100; + wb_thresh *= numerator; + wb_thresh = div64_ul(wb_thresh, denominator); + + wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); + + wb_thresh += (thresh * wb_min_ratio) / 100; + if (wb_thresh > (thresh * wb_max_ratio) / 100) + wb_thresh = thresh * wb_max_ratio / 100; + + return wb_thresh; +} + +unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh) +{ + struct dirty_throttle_control gdtc = { GDTC_INIT(wb), + .thresh = thresh }; + return __wb_calc_thresh(&gdtc); +} + +/* + * 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/wb 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 (wb_dirty < wb_setpoint) scale up pos_ratio + * if (wb_dirty > wb_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) wb control line + * + * ^ pos_ratio + * | + * | * + * | * + * | * + * | * + * | * |<=========== span ============>| + * 1.0 .......................* + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * | . * + * 1/4 ...............................................* * * * * * * * * * * * + * | . . + * | . . + * | . . + * 0 +----------------------.-------------------------------.-------------> + * wb_setpoint^ x_intercept^ + * + * The wb control line won't drop below pos_ratio=1/4, so that wb_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 wb_dirty may rush to many times higher than wb_setpoint. + * - the wb dirty thresh drops quickly due to change of JBOD workload + */ +static void wb_position_ratio(struct dirty_throttle_control *dtc) +{ + struct bdi_writeback *wb = dtc->wb; + unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth); + unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); + unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); + unsigned long wb_thresh = dtc->wb_thresh; + unsigned long x_intercept; + unsigned long setpoint; /* dirty pages' target balance point */ + unsigned long wb_setpoint; + unsigned long span; + long long pos_ratio; /* for scaling up/down the rate limit */ + long x; + + dtc->pos_ratio = 0; + + if (unlikely(dtc->dirty >= limit)) + return; + + /* + * global setpoint + * + * See comment for pos_ratio_polynom(). + */ + setpoint = (freerun + limit) / 2; + pos_ratio = pos_ratio_polynom(setpoint, dtc->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 wb counters + * against wb 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 wb_position_ratio(), we calculate pos_ratio based on + * two values: wb_dirty and wb_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 wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. + * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is + * about ~6K pages (as the average of background and throttle wb + * limits). The 3rd order polynomial will provide positive feedback if + * wb_dirty is under wb_setpoint and vice versa. + * + * Note, that we cannot use global counters in these calculations + * because we want to throttle process writing to a strictlimit wb + * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB + * in the example above). + */ + if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { + long long wb_pos_ratio; + + if (dtc->wb_dirty < 8) { + dtc->pos_ratio = min_t(long long, pos_ratio * 2, + 2 << RATELIMIT_CALC_SHIFT); + return; + } + + if (dtc->wb_dirty >= wb_thresh) + return; + + wb_setpoint = dirty_freerun_ceiling(wb_thresh, + dtc->wb_bg_thresh); + + if (wb_setpoint == 0 || wb_setpoint == wb_thresh) + return; + + wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty, + wb_thresh); + + /* + * Typically, for strictlimit case, wb_setpoint << setpoint + * and pos_ratio >> wb_pos_ratio. In the other words global + * state ("dirty") is not limiting factor and we have to + * make decision based on wb 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 + * wb's) while given strictlimit wb is below limit. + * + * "pos_ratio * wb_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 wb + * 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 wb is well below wb + * 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. + */ + dtc->pos_ratio = min(pos_ratio, wb_pos_ratio); + return; + } + + /* + * We have computed basic pos_ratio above based on global situation. If + * the wb is over/under its share of dirty pages, we want to scale + * pos_ratio further down/up. That is done by the following mechanism. + */ + + /* + * wb setpoint + * + * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint) + * + * x_intercept - wb_dirty + * := -------------------------- + * x_intercept - wb_setpoint + * + * The main wb control line is a linear function that subjects to + * + * (1) f(wb_setpoint) = 1.0 + * (2) k = - 1 / (8 * write_bw) (in single wb case) + * or equally: x_intercept = wb_setpoint + 8 * write_bw + * + * For single wb case, the dirty pages are observed to fluctuate + * regularly within range + * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2] + * for various filesystems, where (2) can yield in a reasonable 12.5% + * fluctuation range for pos_ratio. + * + * For JBOD case, wb_thresh (not wb_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 wb_thresh. + */ + if (unlikely(wb_thresh > dtc->thresh)) + wb_thresh = dtc->thresh; + /* + * It's very possible that wb_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. + */ + wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8); + /* + * scale global setpoint to wb's: + * wb_setpoint = setpoint * wb_thresh / thresh + */ + x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1); + wb_setpoint = setpoint * (u64)x >> 16; + /* + * Use span=(8*write_bw) in single wb case as indicated by + * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case. + * + * wb_thresh thresh - wb_thresh + * span = --------- * (8 * write_bw) + ------------------ * wb_thresh + * thresh thresh + */ + span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16; + x_intercept = wb_setpoint + span; + + if (dtc->wb_dirty < x_intercept - span / 4) { + pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty), + (x_intercept - wb_setpoint) | 1); + } else + pos_ratio /= 4; + + /* + * wb 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 = wb_thresh / 2; + if (dtc->wb_dirty < x_intercept) { + if (dtc->wb_dirty > x_intercept / 8) + pos_ratio = div_u64(pos_ratio * x_intercept, + dtc->wb_dirty); + else + pos_ratio *= 8; + } + + dtc->pos_ratio = pos_ratio; +} + +static void wb_update_write_bandwidth(struct bdi_writeback *wb, + unsigned long elapsed, + unsigned long written) +{ + const unsigned long period = roundup_pow_of_two(3 * HZ); + unsigned long avg = wb->avg_write_bandwidth; + unsigned long old = wb->write_bandwidth; + u64 bw; + + /* + * bw = written * HZ / elapsed + * + * bw * elapsed + write_bandwidth * (period - elapsed) + * write_bandwidth = --------------------------------------------------- + * period + * + * @written may have decreased due to folio_account_redirty(). + * Avoid underflowing @bw calculation. + */ + bw = written - min(written, wb->written_stamp); + bw *= HZ; + if (unlikely(elapsed > period)) { + bw = div64_ul(bw, elapsed); + avg = bw; + goto out; + } + bw += (u64)wb->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: + /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */ + avg = max(avg, 1LU); + if (wb_has_dirty_io(wb)) { + long delta = avg - wb->avg_write_bandwidth; + WARN_ON_ONCE(atomic_long_add_return(delta, + &wb->bdi->tot_write_bandwidth) <= 0); + } + wb->write_bandwidth = bw; + WRITE_ONCE(wb->avg_write_bandwidth, avg); +} + +static void update_dirty_limit(struct dirty_throttle_control *dtc) +{ + struct wb_domain *dom = dtc_dom(dtc); + unsigned long thresh = dtc->thresh; + unsigned long limit = dom->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 + * dom->dirty_limit which is guaranteed to lie above the dirty pages. + */ + thresh = max(thresh, dtc->dirty); + if (limit > thresh) { + limit -= (limit - thresh) >> 5; + goto update; + } + return; +update: + dom->dirty_limit = limit; +} + +static void domain_update_dirty_limit(struct dirty_throttle_control *dtc, + unsigned long now) +{ + struct wb_domain *dom = dtc_dom(dtc); + + /* + * check locklessly first to optimize away locking for the most time + */ + if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) + return; + + spin_lock(&dom->lock); + if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) { + update_dirty_limit(dtc); + dom->dirty_limit_tstamp = now; + } + spin_unlock(&dom->lock); +} + +/* + * Maintain wb->dirty_ratelimit, the base dirty throttle rate. + * + * Normal wb 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 wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, + unsigned long dirtied, + unsigned long elapsed) +{ + struct bdi_writeback *wb = dtc->wb; + unsigned long dirty = dtc->dirty; + unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); + unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); + unsigned long setpoint = (freerun + limit) / 2; + unsigned long write_bw = wb->avg_write_bandwidth; + unsigned long dirty_ratelimit = wb->dirty_ratelimit; + unsigned long dirty_rate; + unsigned long task_ratelimit; + unsigned long balanced_dirty_ratelimit; + unsigned long step; + unsigned long x; + unsigned long shift; + + /* + * 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 - wb->dirtied_stamp) * HZ / elapsed; + + /* + * task_ratelimit reflects each dd's dirty rate for the past 200ms. + */ + task_ratelimit = (u64)dirty_ratelimit * + dtc->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 wb'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: + * + * wb->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 wb counters + * and limits (starting from pos_ratio = wb_position_ratio() and up to + * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). + * Hence, to calculate "step" properly, we have to use wb_dirty as + * "dirty" and wb_setpoint as "setpoint". + * + * We rampup dirty_ratelimit forcibly if wb_dirty is low because + * it's possible that wb_thresh is close to zero due to inactivity + * of backing device. + */ + if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { + dirty = dtc->wb_dirty; + if (dtc->wb_dirty < 8) + setpoint = dtc->wb_dirty + 1; + else + setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; + } + + if (dirty < setpoint) { + x = min3(wb->balanced_dirty_ratelimit, + balanced_dirty_ratelimit, task_ratelimit); + if (dirty_ratelimit < x) + step = x - dirty_ratelimit; + } else { + x = max3(wb->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. + */ + shift = dirty_ratelimit / (2 * step + 1); + if (shift < BITS_PER_LONG) + step = DIV_ROUND_UP(step >> shift, 8); + else + step = 0; + + if (dirty_ratelimit < balanced_dirty_ratelimit) + dirty_ratelimit += step; + else + dirty_ratelimit -= step; + + WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL)); + wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit; + + trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit); +} + +static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, + struct dirty_throttle_control *mdtc, + bool update_ratelimit) +{ + struct bdi_writeback *wb = gdtc->wb; + unsigned long now = jiffies; + unsigned long elapsed; + unsigned long dirtied; + unsigned long written; + + spin_lock(&wb->list_lock); + + /* + * Lockless checks for elapsed time are racy and delayed update after + * IO completion doesn't do it at all (to make sure written pages are + * accounted reasonably quickly). Make sure elapsed >= 1 to avoid + * division errors. + */ + elapsed = max(now - wb->bw_time_stamp, 1UL); + dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]); + written = percpu_counter_read(&wb->stat[WB_WRITTEN]); + + if (update_ratelimit) { + domain_update_dirty_limit(gdtc, now); + wb_update_dirty_ratelimit(gdtc, dirtied, elapsed); + + /* + * @mdtc is always NULL if !CGROUP_WRITEBACK but the + * compiler has no way to figure that out. Help it. + */ + if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) { + domain_update_dirty_limit(mdtc, now); + wb_update_dirty_ratelimit(mdtc, dirtied, elapsed); + } + } + wb_update_write_bandwidth(wb, elapsed, written); + + wb->dirtied_stamp = dirtied; + wb->written_stamp = written; + WRITE_ONCE(wb->bw_time_stamp, now); + spin_unlock(&wb->list_lock); +} + +void wb_update_bandwidth(struct bdi_writeback *wb) +{ + struct dirty_throttle_control gdtc = { GDTC_INIT(wb) }; + + __wb_update_bandwidth(&gdtc, NULL, false); +} + +/* Interval after which we consider wb idle and don't estimate bandwidth */ +#define WB_BANDWIDTH_IDLE_JIF (HZ) + +static void wb_bandwidth_estimate_start(struct bdi_writeback *wb) +{ + unsigned long now = jiffies; + unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp); + + if (elapsed > WB_BANDWIDTH_IDLE_JIF && + !atomic_read(&wb->writeback_inodes)) { + spin_lock(&wb->list_lock); + wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED); + wb->written_stamp = wb_stat(wb, WB_WRITTEN); + WRITE_ONCE(wb->bw_time_stamp, now); + spin_unlock(&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_zone_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 wb_max_pause(struct bdi_writeback *wb, + unsigned long wb_dirty) +{ + unsigned long bw = READ_ONCE(wb->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 = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); + t++; + + return min_t(unsigned long, t, MAX_PAUSE); +} + +static long wb_min_pause(struct bdi_writeback *wb, + long max_pause, + unsigned long task_ratelimit, + unsigned long dirty_ratelimit, + int *nr_dirtied_pause) +{ + long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth)); + long lo = ilog2(READ_ONCE(wb->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 wb_dirty_limits(struct dirty_throttle_control *dtc) +{ + struct bdi_writeback *wb = dtc->wb; + unsigned long wb_reclaimable; + + /* + * wb_thresh is not treated as some limiting factor as + * dirty_thresh, due to reasons + * - in JBOD setup, wb_thresh can fluctuate a lot + * - in a system with HDD and USB key, the USB key may somehow + * go into state (wb_dirty >> wb_thresh) either because + * wb_dirty starts high, or because wb_thresh drops low. + * In this case we don't want to hard throttle the USB key + * dirtiers for 100 seconds until wb_dirty drops under + * wb_thresh. Instead the auxiliary wb control line in + * wb_position_ratio() will let the dirtier task progress + * at some rate <= (write_bw / 2) for bringing down wb_dirty. + */ + dtc->wb_thresh = __wb_calc_thresh(dtc); + dtc->wb_bg_thresh = dtc->thresh ? + div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->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 (dtc->wb_thresh < 2 * wb_stat_error()) { + wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); + dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK); + } else { + wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE); + dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_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 int balance_dirty_pages(struct bdi_writeback *wb, + unsigned long pages_dirtied, unsigned int flags) +{ + struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; + struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; + struct dirty_throttle_control * const gdtc = &gdtc_stor; + struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? + &mdtc_stor : NULL; + struct dirty_throttle_control *sdtc; + unsigned long nr_reclaimable; /* = file_dirty */ + 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; + struct backing_dev_info *bdi = wb->bdi; + bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; + unsigned long start_time = jiffies; + int ret = 0; + + for (;;) { + unsigned long now = jiffies; + unsigned long dirty, thresh, bg_thresh; + unsigned long m_dirty = 0; /* stop bogus uninit warnings */ + unsigned long m_thresh = 0; + unsigned long m_bg_thresh = 0; + + nr_reclaimable = global_node_page_state(NR_FILE_DIRTY); + gdtc->avail = global_dirtyable_memory(); + gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK); + + domain_dirty_limits(gdtc); + + if (unlikely(strictlimit)) { + wb_dirty_limits(gdtc); + + dirty = gdtc->wb_dirty; + thresh = gdtc->wb_thresh; + bg_thresh = gdtc->wb_bg_thresh; + } else { + dirty = gdtc->dirty; + thresh = gdtc->thresh; + bg_thresh = gdtc->bg_thresh; + } + + if (mdtc) { + unsigned long filepages, headroom, writeback; + + /* + * If @wb belongs to !root memcg, repeat the same + * basic calculations for the memcg domain. + */ + mem_cgroup_wb_stats(wb, &filepages, &headroom, + &mdtc->dirty, &writeback); + mdtc->dirty += writeback; + mdtc_calc_avail(mdtc, filepages, headroom); + + domain_dirty_limits(mdtc); + + if (unlikely(strictlimit)) { + wb_dirty_limits(mdtc); + m_dirty = mdtc->wb_dirty; + m_thresh = mdtc->wb_thresh; + m_bg_thresh = mdtc->wb_bg_thresh; + } else { + m_dirty = mdtc->dirty; + m_thresh = mdtc->thresh; + m_bg_thresh = mdtc->bg_thresh; + } + } + + /* + * 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 && nr_reclaimable > gdtc->bg_thresh && + !writeback_in_progress(wb)) + wb_start_background_writeback(wb); + + /* + * Throttle it only when the background writeback cannot + * catch-up. This avoids (excessively) small writeouts + * when the wb limits are ramping up in case of !strictlimit. + * + * In strictlimit case make decision based on the wb counters + * and limits. Small writeouts when the wb limits are ramping + * up are the price we consciously pay for strictlimit-ing. + * + * If memcg domain is in effect, @dirty should be under + * both global and memcg freerun ceilings. + */ + if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) && + (!mdtc || + m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { + unsigned long intv; + unsigned long m_intv; + +free_running: + intv = dirty_poll_interval(dirty, thresh); + m_intv = ULONG_MAX; + + current->dirty_paused_when = now; + current->nr_dirtied = 0; + if (mdtc) + m_intv = dirty_poll_interval(m_dirty, m_thresh); + current->nr_dirtied_pause = min(intv, m_intv); + break; + } + + /* Start writeback even when in laptop mode */ + if (unlikely(!writeback_in_progress(wb))) + wb_start_background_writeback(wb); + + mem_cgroup_flush_foreign(wb); + + /* + * Calculate global domain's pos_ratio and select the + * global dtc by default. + */ + if (!strictlimit) { + wb_dirty_limits(gdtc); + + if ((current->flags & PF_LOCAL_THROTTLE) && + gdtc->wb_dirty < + dirty_freerun_ceiling(gdtc->wb_thresh, + gdtc->wb_bg_thresh)) + /* + * LOCAL_THROTTLE tasks must not be throttled + * when below the per-wb freerun ceiling. + */ + goto free_running; + } + + dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) && + ((gdtc->dirty > gdtc->thresh) || strictlimit); + + wb_position_ratio(gdtc); + sdtc = gdtc; + + if (mdtc) { + /* + * If memcg domain is in effect, calculate its + * pos_ratio. @wb should satisfy constraints from + * both global and memcg domains. Choose the one + * w/ lower pos_ratio. + */ + if (!strictlimit) { + wb_dirty_limits(mdtc); + + if ((current->flags & PF_LOCAL_THROTTLE) && + mdtc->wb_dirty < + dirty_freerun_ceiling(mdtc->wb_thresh, + mdtc->wb_bg_thresh)) + /* + * LOCAL_THROTTLE tasks must not be + * throttled when below the per-wb + * freerun ceiling. + */ + goto free_running; + } + dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) && + ((mdtc->dirty > mdtc->thresh) || strictlimit); + + wb_position_ratio(mdtc); + if (mdtc->pos_ratio < gdtc->pos_ratio) + sdtc = mdtc; + } + + if (dirty_exceeded != wb->dirty_exceeded) + wb->dirty_exceeded = dirty_exceeded; + + if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + + BANDWIDTH_INTERVAL)) + __wb_update_bandwidth(gdtc, mdtc, true); + + /* throttle according to the chosen dtc */ + dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit); + task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >> + RATELIMIT_CALC_SHIFT; + max_pause = wb_max_pause(wb, sdtc->wb_dirty); + min_pause = wb_min_pause(wb, 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(wb, + sdtc->thresh, + sdtc->bg_thresh, + sdtc->dirty, + sdtc->wb_thresh, + sdtc->wb_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(wb, + sdtc->thresh, + sdtc->bg_thresh, + sdtc->dirty, + sdtc->wb_thresh, + sdtc->wb_dirty, + dirty_ratelimit, + task_ratelimit, + pages_dirtied, + period, + pause, + start_time); + if (flags & BDP_ASYNC) { + ret = -EAGAIN; + break; + } + __set_current_state(TASK_KILLABLE); + wb->dirty_sleep = now; + 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 (dirty < thresh) and can also + * keep "1000+ dd on a slow USB stick" under control. + */ + if (task_ratelimit) + break; + + /* + * In the case of an unresponsive NFS server and the NFS dirty + * pages exceeds dirty_thresh, give the other good wb's a pipe + * to go through, so that tasks on them still remain responsive. + * + * In theory 1 page is enough to keep the consumer-producer + * pipe going: the flusher cleans 1 page => the task dirties 1 + * more page. However wb_dirty has accounting errors. So use + * the larger and more IO friendly wb_stat_error. + */ + if (sdtc->wb_dirty <= wb_stat_error()) + break; + + if (fatal_signal_pending(current)) + break; + } + return ret; +} + +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_flags - Balance dirty memory state. + * @mapping: address_space which was dirtied. + * @flags: BDP flags. + * + * 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. + * + * See balance_dirty_pages_ratelimited() for details. + * + * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to + * indicate that memory is out of balance and the caller must wait + * for I/O to complete. Otherwise, it will return 0 to indicate + * that either memory was already in balance, or it was able to sleep + * until the amount of dirty memory returned to balance. + */ +int balance_dirty_pages_ratelimited_flags(struct address_space *mapping, + unsigned int flags) +{ + struct inode *inode = mapping->host; + struct backing_dev_info *bdi = inode_to_bdi(inode); + struct bdi_writeback *wb = NULL; + int ratelimit; + int ret = 0; + int *p; + + if (!(bdi->capabilities & BDI_CAP_WRITEBACK)) + return ret; + + if (inode_cgwb_enabled(inode)) + wb = wb_get_create_current(bdi, GFP_KERNEL); + if (!wb) + wb = &bdi->wb; + + ratelimit = current->nr_dirtied_pause; + if (wb->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)) + ret = balance_dirty_pages(wb, current->nr_dirtied, flags); + + wb_put(wb); + return ret; +} +EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags); + +/** + * 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. + * + * 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) +{ + balance_dirty_pages_ratelimited_flags(mapping, 0); +} +EXPORT_SYMBOL(balance_dirty_pages_ratelimited); + +/** + * wb_over_bg_thresh - does @wb need to be written back? + * @wb: bdi_writeback of interest + * + * Determines whether background writeback should keep writing @wb or it's + * clean enough. + * + * Return: %true if writeback should continue. + */ +bool wb_over_bg_thresh(struct bdi_writeback *wb) +{ + struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; + struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; + struct dirty_throttle_control * const gdtc = &gdtc_stor; + struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? + &mdtc_stor : NULL; + unsigned long reclaimable; + unsigned long thresh; + + /* + * Similar to balance_dirty_pages() but ignores pages being written + * as we're trying to decide whether to put more under writeback. + */ + gdtc->avail = global_dirtyable_memory(); + gdtc->dirty = global_node_page_state(NR_FILE_DIRTY); + domain_dirty_limits(gdtc); + + if (gdtc->dirty > gdtc->bg_thresh) + return true; + + thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh); + if (thresh < 2 * wb_stat_error()) + reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); + else + reclaimable = wb_stat(wb, WB_RECLAIMABLE); + + if (reclaimable > thresh) + return true; + + if (mdtc) { + unsigned long filepages, headroom, writeback; + + mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty, + &writeback); + mdtc_calc_avail(mdtc, filepages, headroom); + domain_dirty_limits(mdtc); /* ditto, ignore writeback */ + + if (mdtc->dirty > mdtc->bg_thresh) + return true; + + thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh); + if (thresh < 2 * wb_stat_error()) + reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); + else + reclaimable = wb_stat(wb, WB_RECLAIMABLE); + + if (reclaimable > thresh) + return true; + } + + return false; +} + +#ifdef CONFIG_SYSCTL +/* + * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs + */ +static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + unsigned int old_interval = dirty_writeback_interval; + int ret; + + ret = proc_dointvec(table, write, buffer, length, ppos); + + /* + * Writing 0 to dirty_writeback_interval will disable periodic writeback + * and a different non-zero value will wakeup the writeback threads. + * wb_wakeup_delayed() would be more appropriate, but it's a pain to + * iterate over all bdis and wbs. + * The reason we do this is to make the change take effect immediately. + */ + if (!ret && write && dirty_writeback_interval && + dirty_writeback_interval != old_interval) + wakeup_flusher_threads(WB_REASON_PERIODIC); + + return ret; +} +#endif + +void laptop_mode_timer_fn(struct timer_list *t) +{ + struct backing_dev_info *backing_dev_info = + from_timer(backing_dev_info, t, laptop_mode_wb_timer); + + wakeup_flusher_threads_bdi(backing_dev_info, 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(); +} + +/* + * 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. + * + * 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) +{ + struct wb_domain *dom = &global_wb_domain; + unsigned long background_thresh; + unsigned long dirty_thresh; + + global_dirty_limits(&background_thresh, &dirty_thresh); + dom->dirty_limit = dirty_thresh; + ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); + if (ratelimit_pages < 16) + ratelimit_pages = 16; +} + +static int page_writeback_cpu_online(unsigned int cpu) +{ + writeback_set_ratelimit(); + return 0; +} + +#ifdef CONFIG_SYSCTL + +/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */ +static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE; + +static struct ctl_table vm_page_writeback_sysctls[] = { + { + .procname = "dirty_background_ratio", + .data = &dirty_background_ratio, + .maxlen = sizeof(dirty_background_ratio), + .mode = 0644, + .proc_handler = dirty_background_ratio_handler, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE_HUNDRED, + }, + { + .procname = "dirty_background_bytes", + .data = &dirty_background_bytes, + .maxlen = sizeof(dirty_background_bytes), + .mode = 0644, + .proc_handler = dirty_background_bytes_handler, + .extra1 = SYSCTL_LONG_ONE, + }, + { + .procname = "dirty_ratio", + .data = &vm_dirty_ratio, + .maxlen = sizeof(vm_dirty_ratio), + .mode = 0644, + .proc_handler = dirty_ratio_handler, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE_HUNDRED, + }, + { + .procname = "dirty_bytes", + .data = &vm_dirty_bytes, + .maxlen = sizeof(vm_dirty_bytes), + .mode = 0644, + .proc_handler = dirty_bytes_handler, + .extra1 = (void *)&dirty_bytes_min, + }, + { + .procname = "dirty_writeback_centisecs", + .data = &dirty_writeback_interval, + .maxlen = sizeof(dirty_writeback_interval), + .mode = 0644, + .proc_handler = dirty_writeback_centisecs_handler, + }, + { + .procname = "dirty_expire_centisecs", + .data = &dirty_expire_interval, + .maxlen = sizeof(dirty_expire_interval), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + }, +#ifdef CONFIG_HIGHMEM + { + .procname = "highmem_is_dirtyable", + .data = &vm_highmem_is_dirtyable, + .maxlen = sizeof(vm_highmem_is_dirtyable), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, +#endif + { + .procname = "laptop_mode", + .data = &laptop_mode, + .maxlen = sizeof(laptop_mode), + .mode = 0644, + .proc_handler = proc_dointvec_jiffies, + }, + {} +}; +#endif + +/* + * 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. + * + * 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, 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) +{ + BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL)); + + cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online", + page_writeback_cpu_online, NULL); + cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL, + page_writeback_cpu_online); +#ifdef CONFIG_SYSCTL + register_sysctl_init("vm", vm_page_writeback_sysctls); +#endif +} + +/** + * 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). + */ +void tag_pages_for_writeback(struct address_space *mapping, + pgoff_t start, pgoff_t end) +{ + XA_STATE(xas, &mapping->i_pages, start); + unsigned int tagged = 0; + void *page; + + xas_lock_irq(&xas); + xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) { + xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE); + if (++tagged % XA_CHECK_SCHED) + continue; + + xas_pause(&xas); + xas_unlock_irq(&xas); + cond_resched(); + xas_lock_irq(&xas); + } + xas_unlock_irq(&xas); +} +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). + * + * To avoid deadlocks between range_cyclic writeback and callers that hold + * pages in PageWriteback to aggregate IO until write_cache_pages() returns, + * we do not loop back to the start of the file. Doing so causes a page + * lock/page writeback access order inversion - we should only ever lock + * multiple pages in ascending page->index order, and looping back to the start + * of the file violates that rule and causes deadlocks. + * + * Return: %0 on success, negative error code otherwise + */ +int write_cache_pages(struct address_space *mapping, + struct writeback_control *wbc, writepage_t writepage, + void *data) +{ + int ret = 0; + int done = 0; + int error; + struct pagevec pvec; + int nr_pages; + pgoff_t index; + pgoff_t end; /* Inclusive */ + pgoff_t done_index; + int range_whole = 0; + xa_mark_t tag; + + pagevec_init(&pvec); + if (wbc->range_cyclic) { + index = mapping->writeback_index; /* prev offset */ + end = -1; + } else { + index = wbc->range_start >> PAGE_SHIFT; + end = wbc->range_end >> PAGE_SHIFT; + if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) + range_whole = 1; + } + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) { + tag_pages_for_writeback(mapping, index, end); + tag = PAGECACHE_TAG_TOWRITE; + } else { + tag = PAGECACHE_TAG_DIRTY; + } + done_index = index; + while (!done && (index <= end)) { + int i; + + nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end, + tag); + if (nr_pages == 0) + break; + + for (i = 0; i < nr_pages; i++) { + struct page *page = pvec.pages[i]; + + 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 integrity 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)); + error = (*writepage)(page, wbc, data); + if (unlikely(error)) { + /* + * Handle errors according to the type of + * writeback. There's no need to continue for + * background writeback. Just push done_index + * past this page so media errors won't choke + * writeout for the entire file. For integrity + * writeback, we must process the entire dirty + * set regardless of errors because the fs may + * still have state to clear for each page. In + * that case we continue processing and return + * the first error. + */ + if (error == AOP_WRITEPAGE_ACTIVATE) { + unlock_page(page); + error = 0; + } else if (wbc->sync_mode != WB_SYNC_ALL) { + ret = error; + done_index = page->index + 1; + done = 1; + break; + } + if (!ret) + ret = error; + } + + /* + * 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 we hit the last page and there is more work to be done: wrap + * back the index back to the start of the file for the next + * time we are called. + */ + if (wbc->range_cyclic && !done) + done_index = 0; + 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. + * + * Return: %0 on success, negative error code otherwise + */ +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; + struct bdi_writeback *wb; + + if (wbc->nr_to_write <= 0) + return 0; + wb = inode_to_wb_wbc(mapping->host, wbc); + wb_bandwidth_estimate_start(wb); + while (1) { + if (mapping->a_ops->writepages) + ret = mapping->a_ops->writepages(mapping, wbc); + else + ret = generic_writepages(mapping, wbc); + if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL)) + break; + + /* + * Lacking an allocation context or the locality or writeback + * state of any of the inode's pages, throttle based on + * writeback activity on the local node. It's as good a + * guess as any. + */ + reclaim_throttle(NODE_DATA(numa_node_id()), + VMSCAN_THROTTLE_WRITEBACK); + } + /* + * Usually few pages are written by now from those we've just submitted + * but if there's constant writeback being submitted, this makes sure + * writeback bandwidth is updated once in a while. + */ + if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + + BANDWIDTH_INTERVAL)) + wb_update_bandwidth(wb); + return ret; +} + +/** + * folio_write_one - write out a single folio and wait on I/O. + * @folio: The folio to write. + * + * The folio must be locked by the caller and will be unlocked upon return. + * + * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this + * function returns. + * + * Return: %0 on success, negative error code otherwise + */ +int folio_write_one(struct folio *folio) +{ + struct address_space *mapping = folio->mapping; + int ret = 0; + struct writeback_control wbc = { + .sync_mode = WB_SYNC_ALL, + .nr_to_write = folio_nr_pages(folio), + }; + + BUG_ON(!folio_test_locked(folio)); + + folio_wait_writeback(folio); + + if (folio_clear_dirty_for_io(folio)) { + folio_get(folio); + ret = mapping->a_ops->writepage(&folio->page, &wbc); + if (ret == 0) + folio_wait_writeback(folio); + folio_put(folio); + } else { + folio_unlock(folio); + } + + if (!ret) + ret = filemap_check_errors(mapping); + return ret; +} +EXPORT_SYMBOL(folio_write_one); + +/* + * For address_spaces which do not use buffers nor write back. + */ +bool noop_dirty_folio(struct address_space *mapping, struct folio *folio) +{ + if (!folio_test_dirty(folio)) + return !folio_test_set_dirty(folio); + return false; +} +EXPORT_SYMBOL(noop_dirty_folio); + +/* + * Helper function for set_page_dirty family. + * + * Caller must hold lock_page_memcg(). + * + * NOTE: This relies on being atomic wrt interrupts. + */ +static void folio_account_dirtied(struct folio *folio, + struct address_space *mapping) +{ + struct inode *inode = mapping->host; + + trace_writeback_dirty_folio(folio, mapping); + + if (mapping_can_writeback(mapping)) { + struct bdi_writeback *wb; + long nr = folio_nr_pages(folio); + + inode_attach_wb(inode, &folio->page); + wb = inode_to_wb(inode); + + __lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr); + __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr); + __node_stat_mod_folio(folio, NR_DIRTIED, nr); + wb_stat_mod(wb, WB_RECLAIMABLE, nr); + wb_stat_mod(wb, WB_DIRTIED, nr); + task_io_account_write(nr * PAGE_SIZE); + current->nr_dirtied += nr; + __this_cpu_add(bdp_ratelimits, nr); + + mem_cgroup_track_foreign_dirty(folio, wb); + } +} + +/* + * Helper function for deaccounting dirty page without writeback. + * + * Caller must hold lock_page_memcg(). + */ +void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb) +{ + long nr = folio_nr_pages(folio); + + lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr); + zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); + wb_stat_mod(wb, WB_RECLAIMABLE, -nr); + task_io_account_cancelled_write(nr * PAGE_SIZE); +} + +/* + * Mark the folio dirty, and set it dirty in the page cache, and mark + * the inode dirty. + * + * If warn is true, then emit a warning if the folio is not uptodate and has + * not been truncated. + * + * The caller must hold lock_page_memcg(). Most callers have the folio + * locked. A few have the folio blocked from truncation through other + * means (eg zap_page_range() has it mapped and is holding the page table + * lock). This can also be called from mark_buffer_dirty(), which I + * cannot prove is always protected against truncate. + */ +void __folio_mark_dirty(struct folio *folio, struct address_space *mapping, + int warn) +{ + unsigned long flags; + + xa_lock_irqsave(&mapping->i_pages, flags); + if (folio->mapping) { /* Race with truncate? */ + WARN_ON_ONCE(warn && !folio_test_uptodate(folio)); + folio_account_dirtied(folio, mapping); + __xa_set_mark(&mapping->i_pages, folio_index(folio), + PAGECACHE_TAG_DIRTY); + } + xa_unlock_irqrestore(&mapping->i_pages, flags); +} + +/** + * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads. + * @mapping: Address space this folio belongs to. + * @folio: Folio to be marked as dirty. + * + * Filesystems which do not use buffer heads should call this function + * from their set_page_dirty address space operation. It ignores the + * contents of folio_get_private(), so if the filesystem marks individual + * blocks as dirty, the filesystem should handle that itself. + * + * This is also sometimes used by filesystems which use buffer_heads when + * a single buffer is being dirtied: we want to set the folio dirty in + * that case, but not all the buffers. This is a "bottom-up" dirtying, + * whereas block_dirty_folio() is a "top-down" dirtying. + * + * The caller must ensure this doesn't race with truncation. Most will + * simply hold the folio lock, but e.g. zap_pte_range() calls with the + * folio mapped and the pte lock held, which also locks out truncation. + */ +bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio) +{ + folio_memcg_lock(folio); + if (folio_test_set_dirty(folio)) { + folio_memcg_unlock(folio); + return false; + } + + __folio_mark_dirty(folio, mapping, !folio_test_private(folio)); + folio_memcg_unlock(folio); + + if (mapping->host) { + /* !PageAnon && !swapper_space */ + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); + } + return true; +} +EXPORT_SYMBOL(filemap_dirty_folio); + +/** + * folio_account_redirty - Manually account for redirtying a page. + * @folio: The folio which is being redirtied. + * + * Most filesystems should call folio_redirty_for_writepage() instead + * of this fuction. If your filesystem is doing writeback outside the + * context of a writeback_control(), it can call this when redirtying + * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED, + * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN, + * WB_WRITTEN) in long term. The mismatches will lead to systematic errors + * in balanced_dirty_ratelimit and the dirty pages position control. + */ +void folio_account_redirty(struct folio *folio) +{ + struct address_space *mapping = folio->mapping; + + if (mapping && mapping_can_writeback(mapping)) { + struct inode *inode = mapping->host; + struct bdi_writeback *wb; + struct wb_lock_cookie cookie = {}; + long nr = folio_nr_pages(folio); + + wb = unlocked_inode_to_wb_begin(inode, &cookie); + current->nr_dirtied -= nr; + node_stat_mod_folio(folio, NR_DIRTIED, -nr); + wb_stat_mod(wb, WB_DIRTIED, -nr); + unlocked_inode_to_wb_end(inode, &cookie); + } +} +EXPORT_SYMBOL(folio_account_redirty); + +/** + * folio_redirty_for_writepage - Decline to write a dirty folio. + * @wbc: The writeback control. + * @folio: The folio. + * + * When a writepage implementation decides that it doesn't want to write + * @folio for some reason, it should call this function, unlock @folio and + * return 0. + * + * Return: True if we redirtied the folio. False if someone else dirtied + * it first. + */ +bool folio_redirty_for_writepage(struct writeback_control *wbc, + struct folio *folio) +{ + bool ret; + long nr = folio_nr_pages(folio); + + wbc->pages_skipped += nr; + ret = filemap_dirty_folio(folio->mapping, folio); + folio_account_redirty(folio); + + return ret; +} +EXPORT_SYMBOL(folio_redirty_for_writepage); + +/** + * folio_mark_dirty - Mark a folio as being modified. + * @folio: The folio. + * + * The folio may not be truncated while this function is running. + * Holding the folio lock is sufficient to prevent truncation, but some + * callers cannot acquire a sleeping lock. These callers instead hold + * the page table lock for a page table which contains at least one page + * in this folio. Truncation will block on the page table lock as it + * unmaps pages before removing the folio from its mapping. + * + * Return: True if the folio was newly dirtied, false if it was already dirty. + */ +bool folio_mark_dirty(struct folio *folio) +{ + struct address_space *mapping = folio_mapping(folio); + + if (likely(mapping)) { + /* + * readahead/lru_deactivate_page could remain + * PG_readahead/PG_reclaim due to race with folio_end_writeback + * About readahead, if the folio is written, the flags would be + * reset. So no problem. + * About lru_deactivate_page, if the folio is redirtied, + * the flag will be reset. So no problem. but if the + * folio is used by readahead it will confuse readahead + * and make it restart the size rampup process. But it's + * a trivial problem. + */ + if (folio_test_reclaim(folio)) + folio_clear_reclaim(folio); + return mapping->a_ops->dirty_folio(mapping, folio); + } + + return noop_dirty_folio(mapping, folio); +} +EXPORT_SYMBOL(folio_mark_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); + +/* + * This cancels just the dirty bit on the kernel page itself, it does NOT + * actually remove dirty bits on any mmap's that may be around. It also + * leaves the page tagged dirty, so any sync activity will still find it on + * the dirty lists, and in particular, clear_page_dirty_for_io() will still + * look at the dirty bits in the VM. + * + * 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 __folio_cancel_dirty(struct folio *folio) +{ + struct address_space *mapping = folio_mapping(folio); + + if (mapping_can_writeback(mapping)) { + struct inode *inode = mapping->host; + struct bdi_writeback *wb; + struct wb_lock_cookie cookie = {}; + + folio_memcg_lock(folio); + wb = unlocked_inode_to_wb_begin(inode, &cookie); + + if (folio_test_clear_dirty(folio)) + folio_account_cleaned(folio, wb); + + unlocked_inode_to_wb_end(inode, &cookie); + folio_memcg_unlock(folio); + } else { + folio_clear_dirty(folio); + } +} +EXPORT_SYMBOL(__folio_cancel_dirty); + +/* + * Clear a folio's dirty flag, while caring for dirty memory accounting. + * Returns true if the folio was previously dirty. + * + * This is for preparing to put the folio under writeout. We leave + * the folio tagged as dirty in the xarray so that a concurrent + * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk. + * The ->writepage implementation will run either folio_start_writeback() + * or folio_mark_dirty(), at which stage we bring the folio's dirty flag + * and xarray dirty tag back into sync. + * + * This incoherency between the folio's dirty flag and xarray tag is + * unfortunate, but it only exists while the folio is locked. + */ +bool folio_clear_dirty_for_io(struct folio *folio) +{ + struct address_space *mapping = folio_mapping(folio); + bool ret = false; + + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + + if (mapping && mapping_can_writeback(mapping)) { + struct inode *inode = mapping->host; + struct bdi_writeback *wb; + struct wb_lock_cookie cookie = {}; + + /* + * 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 folio dirty if it was + * dirty in a pagetable. Only to then + * (c) clean the folio 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 "folio_mark_dirty(folio)" + * 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 folio "master dirty bit" + * as a serialization point for all the different + * threads doing their things. + */ + if (folio_mkclean(folio)) + folio_mark_dirty(folio); + /* + * We carefully synchronise fault handlers against + * installing a dirty pte and marking the folio dirty + * at this point. We do this by having them hold the + * page lock while dirtying the folio, and folios are + * always locked coming in here, so we get the desired + * exclusion. + */ + wb = unlocked_inode_to_wb_begin(inode, &cookie); + if (folio_test_clear_dirty(folio)) { + long nr = folio_nr_pages(folio); + lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr); + zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); + wb_stat_mod(wb, WB_RECLAIMABLE, -nr); + ret = true; + } + unlocked_inode_to_wb_end(inode, &cookie); + return ret; + } + return folio_test_clear_dirty(folio); +} +EXPORT_SYMBOL(folio_clear_dirty_for_io); + +static void wb_inode_writeback_start(struct bdi_writeback *wb) +{ + atomic_inc(&wb->writeback_inodes); +} + +static void wb_inode_writeback_end(struct bdi_writeback *wb) +{ + unsigned long flags; + atomic_dec(&wb->writeback_inodes); + /* + * Make sure estimate of writeback throughput gets updated after + * writeback completed. We delay the update by BANDWIDTH_INTERVAL + * (which is the interval other bandwidth updates use for batching) so + * that if multiple inodes end writeback at a similar time, they get + * batched into one bandwidth update. + */ + spin_lock_irqsave(&wb->work_lock, flags); + if (test_bit(WB_registered, &wb->state)) + queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL); + spin_unlock_irqrestore(&wb->work_lock, flags); +} + +bool __folio_end_writeback(struct folio *folio) +{ + long nr = folio_nr_pages(folio); + struct address_space *mapping = folio_mapping(folio); + bool ret; + + folio_memcg_lock(folio); + if (mapping && mapping_use_writeback_tags(mapping)) { + struct inode *inode = mapping->host; + struct backing_dev_info *bdi = inode_to_bdi(inode); + unsigned long flags; + + xa_lock_irqsave(&mapping->i_pages, flags); + ret = folio_test_clear_writeback(folio); + if (ret) { + __xa_clear_mark(&mapping->i_pages, folio_index(folio), + PAGECACHE_TAG_WRITEBACK); + if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) { + struct bdi_writeback *wb = inode_to_wb(inode); + + wb_stat_mod(wb, WB_WRITEBACK, -nr); + __wb_writeout_add(wb, nr); + if (!mapping_tagged(mapping, + PAGECACHE_TAG_WRITEBACK)) + wb_inode_writeback_end(wb); + } + } + + if (mapping->host && !mapping_tagged(mapping, + PAGECACHE_TAG_WRITEBACK)) + sb_clear_inode_writeback(mapping->host); + + xa_unlock_irqrestore(&mapping->i_pages, flags); + } else { + ret = folio_test_clear_writeback(folio); + } + if (ret) { + lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr); + zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr); + node_stat_mod_folio(folio, NR_WRITTEN, nr); + } + folio_memcg_unlock(folio); + return ret; +} + +bool __folio_start_writeback(struct folio *folio, bool keep_write) +{ + long nr = folio_nr_pages(folio); + struct address_space *mapping = folio_mapping(folio); + bool ret; + int access_ret; + + folio_memcg_lock(folio); + if (mapping && mapping_use_writeback_tags(mapping)) { + XA_STATE(xas, &mapping->i_pages, folio_index(folio)); + struct inode *inode = mapping->host; + struct backing_dev_info *bdi = inode_to_bdi(inode); + unsigned long flags; + + xas_lock_irqsave(&xas, flags); + xas_load(&xas); + ret = folio_test_set_writeback(folio); + if (!ret) { + bool on_wblist; + + on_wblist = mapping_tagged(mapping, + PAGECACHE_TAG_WRITEBACK); + + xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK); + if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) { + struct bdi_writeback *wb = inode_to_wb(inode); + + wb_stat_mod(wb, WB_WRITEBACK, nr); + if (!on_wblist) + wb_inode_writeback_start(wb); + } + + /* + * We can come through here when swapping + * anonymous folios, so we don't necessarily + * have an inode to track for sync. + */ + if (mapping->host && !on_wblist) + sb_mark_inode_writeback(mapping->host); + } + if (!folio_test_dirty(folio)) + xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY); + if (!keep_write) + xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE); + xas_unlock_irqrestore(&xas, flags); + } else { + ret = folio_test_set_writeback(folio); + } + if (!ret) { + lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr); + zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr); + } + folio_memcg_unlock(folio); + access_ret = arch_make_folio_accessible(folio); + /* + * If writeback has been triggered on a page that cannot be made + * accessible, it is too late to recover here. + */ + VM_BUG_ON_FOLIO(access_ret != 0, folio); + + return ret; +} +EXPORT_SYMBOL(__folio_start_writeback); + +/** + * folio_wait_writeback - Wait for a folio to finish writeback. + * @folio: The folio to wait for. + * + * If the folio is currently being written back to storage, wait for the + * I/O to complete. + * + * Context: Sleeps. Must be called in process context and with + * no spinlocks held. Caller should hold a reference on the folio. + * If the folio is not locked, writeback may start again after writeback + * has finished. + */ +void folio_wait_writeback(struct folio *folio) +{ + while (folio_test_writeback(folio)) { + trace_folio_wait_writeback(folio, folio_mapping(folio)); + folio_wait_bit(folio, PG_writeback); + } +} +EXPORT_SYMBOL_GPL(folio_wait_writeback); + +/** + * folio_wait_writeback_killable - Wait for a folio to finish writeback. + * @folio: The folio to wait for. + * + * If the folio is currently being written back to storage, wait for the + * I/O to complete or a fatal signal to arrive. + * + * Context: Sleeps. Must be called in process context and with + * no spinlocks held. Caller should hold a reference on the folio. + * If the folio is not locked, writeback may start again after writeback + * has finished. + * Return: 0 on success, -EINTR if we get a fatal signal while waiting. + */ +int folio_wait_writeback_killable(struct folio *folio) +{ + while (folio_test_writeback(folio)) { + trace_folio_wait_writeback(folio, folio_mapping(folio)); + if (folio_wait_bit_killable(folio, PG_writeback)) + return -EINTR; + } + + return 0; +} +EXPORT_SYMBOL_GPL(folio_wait_writeback_killable); + +/** + * folio_wait_stable() - wait for writeback to finish, if necessary. + * @folio: The folio to wait on. + * + * This function determines if the given folio is related to a backing + * device that requires folio contents to be held stable during writeback. + * If so, then it will wait for any pending writeback to complete. + * + * Context: Sleeps. Must be called in process context and with + * no spinlocks held. Caller should hold a reference on the folio. + * If the folio is not locked, writeback may start again after writeback + * has finished. + */ +void folio_wait_stable(struct folio *folio) +{ + if (mapping_stable_writes(folio_mapping(folio))) + folio_wait_writeback(folio); +} +EXPORT_SYMBOL_GPL(folio_wait_stable); |