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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /mm/page-writeback.c
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'mm/page-writeback.c')
-rw-r--r--mm/page-writeback.c3084
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);