Quellcode-Bibliothek page-writeback.c
Sprache: C
// 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 . * * 10 Apr2002 Andrew Morton * Initial version #include <linux/kernel.h>#include <linux/math64.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" #include "swap.h" /* * Sleep at most 200 ms 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 or update dirty limit at 200 ms 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 */ /* * 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;/* End of sysctl-exported parameters */ struct wb_domain global_wb_domain;/* * 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), \#define GDTC_INIT_NO_WB .dom = &global_wb_domain#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \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) {if (max < 100 * BDI_RATIO_SCALE) {#else /* CONFIG_CGROUP_WRITEBACK */ #define GDTC_INIT(__wb) .wb = (__wb), \#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)#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 ;/* * 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 . return nr_pages;static unsigned long highmem_dirtyable_memory(unsigned long total)#ifdef CONFIG_HIGHMEMint node;unsigned long x = 0 ;int i;for (i = ZONE_NORMAL + 1 ; i < MAX_NR_ZONES; i++) {struct zone *z;unsigned long nr_pages;if (!is_highmem_idx(i))continue ;if (!populated_zone(z))continue ;/* watch for underflows */ /* * 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;/* * 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 . if (!vm_highmem_is_dirtyable)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)if (bg_bytes)0 ;if (bytes)else if (bg_bytes)else if (rt_or_dl_task(tsk)) {4 + global_wb_domain.dirty_limit / 32 ;4 + global_wb_domain.dirty_limit / 32 ;/* * Dirty throttling logic assumes the limits in page units fit into * 32 - bits . This gives 16 TB dirty limits max which is hopefully enough . if (thresh > UINT_MAX)/* This makes sure bg_thresh is within 32-bits as well */ if (bg_thresh >= thresh)2 ;/* we should eventually report the domain in the TP */ if (!gdtc)/** * 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 };/** * 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)else 100 ;if (rt_or_dl_task(tsk))4 ;/* * Dirty throttling logic assumes the limits in page units fit into * 32 - bits . This gives 16 TB dirty limits max which is hopefully enough . return min_t(unsigned long , dirty, UINT_MAX);/** * 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 ;return nr_pages <= limit;#ifdef CONFIG_SYSCTLstatic int dirty_background_ratio_handler(const struct ctl_table *table, int write,void *buffer, size_t *lenp, loff_t *ppos)int ret;if (ret == 0 && write)0 ;return ret;static int dirty_background_bytes_handler(const struct ctl_table *table, int write,void *buffer, size_t *lenp, loff_t *ppos)int ret;unsigned long old_bytes = dirty_background_bytes;if (ret == 0 && write) {if (DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE) >return -ERANGE;0 ;return ret;static int dirty_ratio_handler(const struct ctl_table *table, int write, void *buffer,int old_ratio = vm_dirty_ratio;int ret;if (ret == 0 && write && vm_dirty_ratio != old_ratio) {0 ;return ret;static int dirty_bytes_handler(const struct ctl_table *table, int write,void *buffer, size_t *lenp, loff_t *ppos)unsigned long old_bytes = vm_dirty_bytes;int ret;if (ret == 0 && write && vm_dirty_bytes != old_bytes) {if (DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) > UINT_MAX) {return -ERANGE;0 ;return ret;#endif static unsigned long wp_next_time(unsigned long cur_time)/* 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)/* First event after period switching was turned off? */ if (unlikely(!dom->period_time)) {/* * We can race with other wb_domain_writeout_add 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 . /* * 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;if (cgdom)void wb_writeout_inc(struct bdi_writeback *wb)unsigned long flags;1 );/* * 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 = timer_container_of(dom, t, period_timer);int miss_periods = (jiffies - dom->period_time) /if (fprop_new_period(&dom->completions, miss_periods + 1 )) {else {/* * Aging has zeroed all fractions . Stop wasting CPU on period * updates . 0 ;int wb_domain_init(struct wb_domain *dom, gfp_t gfp)0 , sizeof (*dom));return fprop_global_init(&dom->completions, gfp);#ifdef CONFIG_CGROUP_WRITEBACKvoid wb_domain_exit(struct wb_domain *dom)#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;static int bdi_check_pages_limit(unsigned long pages)unsigned long max_dirty_pages = global_dirtyable_memory();if (pages > max_dirty_pages)return -EINVAL;return 0 ;static unsigned long bdi_ratio_from_pages(unsigned long pages)unsigned long background_thresh;unsigned long dirty_thresh;unsigned long ratio;if (!dirty_thresh)return -EINVAL;100 ULL * BDI_RATIO_SCALE, dirty_thresh);return ratio;static u64 bdi_get_bytes(unsigned int ratio)unsigned long background_thresh;unsigned long dirty_thresh;100 ;return bytes;static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)unsigned int delta;int ret = 0 ;if (min_ratio > 100 * BDI_RATIO_SCALE)return -EINVAL;if (min_ratio > bdi->max_ratio) {else {if (min_ratio < bdi->min_ratio) {else {if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {else {return ret;static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)int ret = 0 ;if (max_ratio > 100 * BDI_RATIO_SCALE)return -EINVAL;if (bdi->min_ratio > max_ratio) {else {100 * BDI_RATIO_SCALE);return ret;int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)return __bdi_set_min_ratio(bdi, min_ratio);int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)return __bdi_set_max_ratio(bdi, max_ratio);int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);struct backing_dev_info *bdi)return bdi_get_bytes(bdi->min_ratio);int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)int ret;unsigned long pages = min_bytes >> PAGE_SHIFT;long min_ratio;if (ret)return ret;if (min_ratio < 0 )return min_ratio;return __bdi_set_min_ratio(bdi, min_ratio);struct backing_dev_info *bdi)return bdi_get_bytes(bdi->max_ratio);int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)int ret;unsigned long pages = max_bytes >> PAGE_SHIFT;long max_ratio;if (ret)return ret;if (max_ratio < 0 )return max_ratio;return __bdi_set_max_ratio(bdi, max_ratio);int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)if (strict_limit > 1 )return -EINVAL;if (strict_limit)else return 0 ;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);static inline bool dtc_is_global(struct dirty_throttle_control *dtc)return mdtc_gdtc(dtc) == NULL;/* * Dirty background will ignore pages being written as we ' re trying to * decide whether to put more under writeback . static void domain_dirty_avail(struct dirty_throttle_control *dtc,bool include_writeback)if (dtc_is_global(dtc)) {if (include_writeback)else {unsigned long filepages = 0 , headroom = 0 , writeback = 0 ;if (include_writeback)/** * _ _ wb_calc_thresh - @ wb ' s share of dirty threshold * @ dtc : dirty_throttle_context of interest * @ thresh : dirty throttling or dirty background threshold of wb_domain in @ dtc * * Note that balance_dirty_pages ( ) will only seriously take dirty throttling * threshold 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 10 MB / 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 . For dirty throttling limit , 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,unsigned long thresh)struct wb_domain *dom = dtc_dom(dtc);struct bdi_writeback *wb = dtc->wb;unsigned long numerator, denominator;unsigned long wb_min_ratio, wb_max_ratio;/* * Calculate this wb ' s share of the thresh ratio . 100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);100 * BDI_RATIO_SCALE);/* * 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 . if (thresh > dtc->dirty) {if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT))100 );else 8 );100 * BDI_RATIO_SCALE);if (wb_thresh > wb_max_thresh)return wb_thresh;unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };true );return __wb_calc_thresh(&gdtc, thresh);unsigned long cgwb_calc_thresh(struct bdi_writeback *wb)struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };true );true );return __wb_calc_thresh(&mdtc, mdtc.thresh);/* * setpoint - dirty 3 * f ( dirty ) : = 1 . 0 + ( - - - - - - - - - - - - - - - - ) * limit - setpoint * * it ' s a 3 rd 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;1 );1 << RATELIMIT_CALC_SHIFT;return clamp(pos_ratio, 0 LL, 2 LL << 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 = dtc->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;0 ;if (unlikely(dtc->dirty >= limit))return ;/* * global setpoint * * See comment for pos_ratio_polynom ( ) . 2 ;/* * 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 . * * 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 16 GB , 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 16 GB . This amounts to ~ 8 K pages . * wb_calc_thresh ( wb , bg_thresh ) is about ~ 4 K pages . wb_setpoint is * about ~ 6 K pages ( as the average of background and throttle wb * limits ) . The 3 rd 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 ( ~ 23 MB vs . ~ 2 . 3 GB * in the example above ) . if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {long long wb_pos_ratio;if (dtc->wb_dirty >= wb_thresh)return ;if (wb_setpoint == 0 || wb_setpoint == wb_thresh)return ;/* * 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 . 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))/* * scale global setpoint to wb ' s : * wb_setpoint = setpoint * wb_thresh / thresh 16 , dtc->thresh | 1 );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 8 * write_bw) * (u64)x >> 16 ;if (dtc->wb_dirty < x_intercept - span / 4 ) {1 );else 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 . 2 ;if (dtc->wb_dirty < x_intercept) {if (dtc->wb_dirty > x_intercept / 8 )else 8 ;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;/* * bw = written * HZ / elapsed * * bw * elapsed + write_bandwidth * ( period - elapsed ) * write_bandwidth = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * period * * @ written may have decreased due to folio_redirty_for_writepage ( ) . * Avoid underflowing @ bw calculation . if (unlikely(elapsed > period)) {goto out;/* * one more level of smoothing , for filtering out sudden spikes if (avg > old && old >= (unsigned long )bw)3 ;if (avg < old && old <= (unsigned long )bw)3 ;/* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */ 1 LU);if (wb_has_dirty_io(wb)) {long delta = avg - wb->avg_write_bandwidth;0 );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) {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 . if (limit > thresh) {5 ;goto update;return ;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 ;if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {/* * 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 . /* * task_ratelimit reflects each dd ' s dirty rate for the past 200 ms . /* 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 . 1 );/* * balanced_dirty_ratelimit ~ = ( write_bw / N ) < = write_bw if (unlikely(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 200 ms estimation period of dirty_rate ( we want to * keep that period small to reduce time lags ) . 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 " . if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {2 ;if (dirty < setpoint) {if (dirty_ratelimit < x)else {if (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 . 2 * step + 1 );if (shift < BITS_PER_LONG)8 );else 0 ;if (dirty_ratelimit < balanced_dirty_ratelimit)else 1 UL));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;/* * 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 . 1 UL);if (update_ratelimit) {/* * @ 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) {void wb_update_bandwidth(struct bdi_writeback *wb)struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };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 &&/* * 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 1 UL << (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 . 1 + bw / roundup_pow_of_two(1 + HZ / 8 ));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 */ 1 , HZ / 100 );/* * Scale up pause time for concurrent dirtiers in order to reduce CPU * overheads . * * ( N * 10 ms ) on 2 ^ N concurrent tasks . if (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 . 1 + max_pause / 2 );/* * Tiny nr_dirtied_pause is found to hurt I / O performance in the test * case fio - mmap - randwrite - 64 k , 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) {if (pages > DIRTY_POLL_THRESH) {1 );if (pause > max_pause) {/* * 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 . 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()) {else {static unsigned long domain_poll_intv(struct dirty_throttle_control *dtc,bool strictlimit)unsigned long dirty, thresh;if (strictlimit) {else {return dirty_poll_interval(dirty, thresh);/* * 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 . static void domain_dirty_freerun(struct dirty_throttle_control *dtc,bool strictlimit)unsigned long dirty, thresh, bg_thresh;if (unlikely(strictlimit)) {else {static void balance_domain_limits(struct dirty_throttle_control *dtc,bool strictlimit)true );static void wb_dirty_freerun(struct dirty_throttle_control *dtc,bool strictlimit)false ;/* was already handled in domain_dirty_freerun */ if (strictlimit)return ;/* * LOCAL_THROTTLE tasks must not be throttled when below the per - wb * freerun ceiling . if (!(current->flags & PF_LOCAL_THROTTLE))return ;static inline void wb_dirty_exceeded(struct dirty_throttle_control *dtc,bool strictlimit)/* * The limits fields dirty_exceeded and pos_ratio won ' t be updated if wb is * in freerun state . Please don ' t use these invalid fields in freerun case . static void balance_wb_limits(struct dirty_throttle_control *dtc,bool strictlimit)if (dtc->freerun)return ;/* * 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) ?struct dirty_throttle_control *sdtc;unsigned long nr_dirty;long period;long pause;long max_pause;long min_pause;int nr_dirtied_pause;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;if (mdtc) {/* * If @ wb belongs to ! root memcg , repeat the same * basic calculations for the memcg domain . /* * 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_dirty > gdtc->bg_thresh &&/* * If memcg domain is in effect , @ dirty should be under * both global and memcg freerun ceilings . if (gdtc->freerun && (!mdtc || mdtc->freerun)) {unsigned long intv;unsigned long m_intv;0 ;if (mdtc)break ;/* Start writeback even when in laptop mode */ if (unlikely(!writeback_in_progress(wb)))/* * Calculate global domain ' s pos_ratio and select the * global dtc by default . if (gdtc->freerun)goto free_running;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 (mdtc->freerun)goto free_running;if (mdtc->pos_ratio < gdtc->pos_ratio)if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +true );/* throttle according to the chosen dtc */ if (unlikely(task_ratelimit == 0 )) {goto pause;if (current->dirty_paused_when)/* * For less than 1 s think time ( ext3 / 4 may block the dirtier * for up to 800 ms 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) {0 L),if (pause < -HZ) {0 ;else if (period) {0 ;else if (current->nr_dirtied_pause <= pages_dirtied)break ;if (unlikely(pause > max_pause)) {/* for occasional dropped task_ratelimit */ if (flags & BDP_ASYNC) {break ;0 ;/* * 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 . 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))if (!wb)if (wb->dirty_exceeded)32 >> (PAGE_SHIFT - 10 ));/* * 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 . if (unlikely(current->nr_dirtied >= ratelimit))0 ;else if (unlikely(*p >= ratelimit_pages)) {0 ;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 . if (*p > 0 && current->nr_dirtied < ratelimit) {unsigned long nr_pages_dirtied;if (unlikely(current->nr_dirtied >= ratelimit))return ret;/** * 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)0 );/* * Similar to wb_dirty_limits , wb_bg_dirty_limits also calculates dirty * and thresh , but it ' s for background writeback . static void wb_bg_dirty_limits(struct dirty_throttle_control *dtc)struct bdi_writeback *wb = dtc->wb;if (dtc->wb_bg_thresh < 2 * wb_stat_error())else static bool domain_over_bg_thresh(struct dirty_throttle_control *dtc)false );if (dtc->dirty > dtc->bg_thresh)return true ;if (dtc->wb_dirty > dtc->wb_bg_thresh)return true ;return false ;/** * 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 = { GDTC_INIT(wb) };struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };if (domain_over_bg_thresh(&gdtc))return true ;if (mdtc_valid(&mdtc))return domain_over_bg_thresh(&mdtc);return false ;#ifdef CONFIG_SYSCTL/* * sysctl handler for / proc / sys / vm / dirty_writeback_centisecs static int dirty_writeback_centisecs_handler(const struct ctl_table *table, int write,void *buffer, size_t *length, loff_t *ppos)unsigned int old_interval = dirty_writeback_interval;int ret;/* * 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 &&return ret;#endif void laptop_mode_timer_fn(struct timer_list *t)struct backing_dev_info *backing_dev_info =/* * 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)/* * 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;/* * 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;32 );if (ratelimit_pages < 16 )16 ;static int page_writeback_cpu_online(unsigned int cpu)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 const struct ctl_table vm_page_writeback_sysctls[] = {"dirty_background_ratio" ,sizeof (dirty_background_ratio),0644 ,"dirty_background_bytes" ,sizeof (dirty_background_bytes),0644 ,"dirty_ratio" ,sizeof (vm_dirty_ratio),0644 ,"dirty_bytes" ,sizeof (vm_dirty_bytes),0644 ,void *)&dirty_bytes_min,"dirty_writeback_centisecs" ,sizeof (dirty_writeback_interval),0644 ,"dirty_expire_centisecs" ,sizeof (dirty_expire_interval),0644 ,#ifdef CONFIG_HIGHMEM"highmem_is_dirtyable" ,sizeof (vm_highmem_is_dirtyable),0644 ,#endif "laptop_mode" ,sizeof (laptop_mode),0644 ,#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 )"mm/writeback:online" ,"mm/writeback:dead" , NULL,#ifdef CONFIG_SYSCTL"vm" , vm_page_writeback_sysctls);#endif /** * tag_pages_for_writeback - tag pages to be written by writeback * @ 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 caller * can then use the 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,unsigned int tagged = 0 ;void *page;if (++tagged % XA_CHECK_SCHED)continue ;static bool folio_prepare_writeback(struct address_space *mapping,struct writeback_control *wbc, struct folio *folio)/* * Folio truncated or invalidated . We can freely skip it then , * even for data integrity operations : the folio has disappeared * concurrently , so there could be no real expectation of this * data integrity operation even if there is now a new , dirty * folio at the same pagecache index . if (unlikely(folio->mapping != mapping))return false ;/* * Did somebody else write it for us ? if (!folio_test_dirty(folio))return false ;if (folio_test_writeback(folio)) {if (wbc->sync_mode == WB_SYNC_NONE)return false ;if (!folio_clear_dirty_for_io(folio))return false ;return true ;static xa_mark_t wbc_to_tag(struct writeback_control *wbc)if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)return PAGECACHE_TAG_TOWRITE;return PAGECACHE_TAG_DIRTY;static pgoff_t wbc_end(struct writeback_control *wbc)if (wbc->range_cyclic)return -1 ;return wbc->range_end >> PAGE_SHIFT;static struct folio *writeback_get_folio(struct address_space *mapping,struct writeback_control *wbc)struct folio *folio;if (!folio) {if (!folio)return NULL;if (unlikely(!folio_prepare_writeback(mapping, wbc, folio))) {goto retry;return folio;/** * writeback_iter - iterate folio of a mapping for writeback * @ mapping : address space structure to write * @ wbc : writeback context * @ folio : previously iterated folio ( % NULL to start ) * @ error : in - out pointer for writeback errors ( see below ) * * This function returns the next folio for the writeback operation described by * @ wbc on @ mapping and should be called in a while loop in the - > writepages * implementation . * * To start the writeback operation , % NULL is passed in the @ folio argument , and * for every subsequent iteration the folio returned previously should be passed * back in . * * If there was an error in the per - folio writeback inside the writeback_iter ( ) * loop , @ error should be set to the error value . * * Once the writeback described in @ wbc has finished , this function will return * % NULL and if there was an error in any iteration restore it to @ error . * * Note : callers should not manually break out of the loop using break or goto * but must keep calling writeback_iter ( ) until it returns % NULL . * * Return : the folio to write or % NULL if the loop is done . struct folio *writeback_iter(struct address_space *mapping,struct writeback_control *wbc, struct folio *folio, int *error)if (!folio) {0 ;/* * For range cyclic writeback we remember where we stopped so * that we can continue where we stopped . * * For non - cyclic writeback we always start at the beginning of * the passed in range . if (wbc->range_cyclic)else /* * To avoid livelocks when other processes dirty new pages , we * first tag pages which should be written back and only then * start writing them . * * For data - integrity writeback we have to be careful so that we * do not miss some pages ( e . g . , because some other process has * cleared the 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 I / O ) . if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)else {0 );/* * For integrity writeback we have to keep going until we have * written all the folios we tagged for writeback above , even if * we run past wbc - > nr_to_write or encounter errors . * We stash away the first error we encounter in wbc - > saved_err * so that it can be retrieved when we ' re done . This is because * the file system may still have state to clear for each folio . * * For background writeback we exit as soon as we run past * wbc - > nr_to_write or encounter the first error . if (wbc->sync_mode == WB_SYNC_ALL) {if (*error && !wbc->saved_err)else {if (*error || wbc->nr_to_write <= 0 )goto done;if (!folio) {/* * To avoid deadlocks between range_cyclic writeback and callers * that hold folios in writeback to aggregate I / O until * the writeback iteration finishes , we do not loop back to the * start of the file . Doing so causes a folio lock / folio * writeback access order inversion - we should only ever lock * multiple folios in ascending folio - > index order , and looping * back to the start of the file violates that rule and causes * deadlocks . if (wbc->range_cyclic)0 ;/* * Return the first error we encountered ( if there was any ) to * the caller . return folio;if (wbc->range_cyclic)return NULL;/** * 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 * * Return : % 0 on success , negative error code otherwise * * Note : please use writeback_iter ( ) instead . int write_cache_pages(struct address_space *mapping,struct writeback_control *wbc, writepage_t writepage,void *data)struct folio *folio = NULL;int error;while ((folio = writeback_iter(mapping, wbc, folio, &error))) {if (error == AOP_WRITEPAGE_ACTIVATE) {0 ;return error;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 ;while (1 ) {if (mapping->a_ops->writepages)else /* deal with chardevs and other special files */ 0 ;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 . /* * 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) +return ret;/* * 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 ;/* * Helper function for set_page_dirty family . * * 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;if (mapping_can_writeback(mapping)) {struct bdi_writeback *wb;long nr = folio_nr_pages(folio);/* * Helper function for deaccounting dirty page without writeback . * void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)long nr = folio_nr_pages(folio);/* * Mark the folio dirty , and set it dirty in the page cache . * * If warn is true , then emit a warning if the folio is not uptodate and has * not been truncated . * * It is the caller ' s responsibility to prevent the folio from being truncated * while this function is in progress , although it may have been truncated * before this function is called . Most callers have the folio locked . * A few have the folio blocked from truncation through other means ( e . g . * zap_vma_pages ( ) has it mapped and is holding the page table lock ) . * When called from mark_buffer_dirty ( ) , the filesystem should hold a * reference to the buffer_head that is being marked dirty , which causes * try_to_free_buffers ( ) to fail . void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,int warn)unsigned long flags;if (folio->mapping) { /* Race with truncate? */ /** * 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 dirty_folio 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)if (folio_test_set_dirty(folio))return false ;if (mapping->host) {/* !PageAnon && !swapper_space */ return true ;/** * 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)struct address_space *mapping = folio->mapping;long nr = folio_nr_pages(folio);bool ret;if (mapping && mapping_can_writeback(mapping)) {struct inode *inode = mapping->host;struct bdi_writeback *wb;struct wb_lock_cookie cookie = {};return ret;/** * 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 / folio_deactivate 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 folio_deactivate , 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))return mapping->a_ops->dirty_folio(mapping, folio);return noop_dirty_folio(mapping, folio);/* * folio_mark_dirty ( ) is racy if the caller has no reference against * folio - > mapping - > host , and if the folio is unlocked . This is because another * CPU could truncate the folio off the mapping and then free the mapping . * * Usually , the folio _ 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 folio should be locked before running folio_mark_dirty ( ) . bool folio_mark_dirty_lock(struct folio *folio)bool ret;return ret;/* * 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 = {};if (folio_test_clear_dirty(folio))else {/* * 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 ;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))/* * 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 . if (folio_test_clear_dirty(folio)) {long nr = folio_nr_pages(folio);true ;return ret;return folio_test_clear_dirty(folio);static void wb_inode_writeback_start(struct bdi_writeback *wb)static void wb_inode_writeback_end(struct bdi_writeback *wb)unsigned long flags;/* * 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 . if (test_bit(WB_registered, &wb->state))bool __folio_end_writeback(struct folio *folio)long nr = folio_nr_pages(folio);struct address_space *mapping = folio_mapping(folio);bool ret;if (mapping && mapping_use_writeback_tags(mapping)) {struct inode *inode = mapping->host;struct backing_dev_info *bdi = inode_to_bdi(inode);unsigned long flags;1 << PG_writeback);if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {struct bdi_writeback *wb = inode_to_wb(inode);if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))if (mapping->host && !mapping_tagged(mapping,else {1 << PG_writeback);return ret;void __folio_start_writeback(struct folio *folio, bool keep_write)long nr = folio_nr_pages(folio);struct address_space *mapping = folio_mapping(folio);int access_ret;if (mapping && mapping_use_writeback_tags(mapping)) {struct inode *inode = mapping->host;struct backing_dev_info *bdi = inode_to_bdi(inode);unsigned long flags;bool on_wblist;if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {struct bdi_writeback *wb = inode_to_wb(inode);if (!on_wblist)/* * 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)if (!folio_test_dirty(folio))if (!keep_write)else {/* * If writeback has been triggered on a page that cannot be made * accessible , it is too late to recover here . 0 , folio);/** * 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)) {/** * 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)) {if (folio_wait_bit_killable(folio, PG_writeback))return -EINTR;return 0 ;/** * 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)))
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